Blister Busted

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WHAT CAUSES BLISTERS

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SURVEY THE DAMAGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

THE MOISTURE TEST

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R EMOVING BOTTOM COATINGS DRYING TECHNIQUES

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ESTIMATING COVERAGE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

R EPAIR METHODS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

BARRIER COATINGS

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WORKING WITH EPOXY

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PROPER INSTALLATION OF THRU–HULLS PREVENTION

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- SUBSCRIBE / ARCHIVES / HELP / QUIT / TERMS OF USE -

WHAT CAUSES BLISTERS M

Regardless of the quality of construction, osmosis blistering and water absorption into the laminate occur in most boats sooner or later. It's the nature of the beast! Variations in resins, catalysts, humidity and workmanship in the manufacturing process all determine when and to what extent gelcoat blisters appear. —Jan Mundy

AKZO SIKKENS

than 30 years ago, the use of fiberglass and resin to build boats revolutionized the marine manufacturing process.

Renown for high strength, durability and presumed low maintenance, fiberglass was deemed to be almost indestructible. In the early 70s, it was rumored that fiberglass boats were being devoured by "polyestermites." Those in the know compared these glass-eating bugs to the teredo worm, the nemesis of wooden boat owners. It was discovered to be a hoax; although perhaps the mites creators forewarned of what we now call osmosis.

A fiberglass hull is composed of two layers. The base layer, or polyester resinreinforced fiberglass laminate, is covered by gelcoat, a pigmented polyester resin. All fiberglass laminates are semipermeable, meaning they allow water to pass through the outer layers. Osmosis is the process of moisture seeping into the fiberglass laminate, either through the gelcoat layer or internally from the bilge areas. As moisture migrates into the laminate it fills voids, becomes trapped and creates an acidic blister fluid. Still seeking to diffuse equally throughout the substrate, the water between the laminate and outer surface places pressure on the gelcoat. The resulting blemishes or blisters that form between the laminate and the gelcoat affect the appearance and performance of the boat. As excessive moisture is the culprit, blistering usually only occurs below the waterline.

When blisters are left unchecked they will progressively extend deeper into the laminate and affect the structural integrity of the hull. The term used to describe the chemical reaction between polyester resin laminates and water is hydrolysis. Over time, blister fluids attack the resin in the laminate, severing the chemical bond between the resin and laminate. As it progresses, the bottom becomes spongy and delaminates. Unfortunately, this condition is not reversible but can be repaired once it has started. Any hydrolyzed laminate on a boat must be removed and the bottom relaminated.

This usually requires the services of a professional.

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Osmosis starts with a minuscule air bubble trapped between gelcoat and laminate (1). Moisture penetrates the slightly porous gelcoat, causing the blister to expand (2).

Moisture gradually breaks down and dissolves the polyester resin. This watery solution collects in the microscopic voids in the solidified resin, increasing moisture absorption through the gelcoat and creating a highly concentrated, soursmelling substance. This substance builds up pressure and causes blistering of the gelcoat (3). As a result of the pressure build-up, the gelcoat separates from the laminate. The pressure in the blister continues to grow and eventually, causes the blister to burst (4).

Š DIY boat owner 2001 1-888-658-2628

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BLISTERS: FACT VS. FICTION most often occurs between the gelcoat and the outer skin mat layer, some occurs between this mat layer and the structural laminate. (Blisters rarely form in structural laminates of roving layers.) Fibers in the thick mat layer (outer skin) that are not completely saturated with resin (polyester or vinylester) or resin that was not properly catalyzed during the original building creates void spots or air bubbles. Water migration through the laminate collects in these voids and initiates the blistering process. Most boats have some resinstarved mat, sections of dry, uncoated fibers in the outer laminate. The quality of the fiberglass lay-up work plays a major role in blister occurrence and prevention.

Not all blister repair jobs fail, but many do. The main reasons barrier coatings fail are preparation and application of the coating, and poor construction. According to Interlux assistant marketing manager Jim Seidel, failures are most frequently caused by not properly drying the hull prior to coating. A wet hull will continue to blister under the epoxy.

Poor surface preparation, things such as leaving the antifouling paint on or not sanding properly always lead to a poor result. Other reasons for reblistering include improper mixing or incomplete curing, filler material that was not correctly mixed or catalyzed reasons or not applying enough epoxy to gain a proper barrier, usually 10 mils or more.

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LISTERING

"The mistake most people make here is thinking that there is a magic number of coats," said Jim Seidel of Interlux. "Since there is not a good definition of what a coat is, you must figure out how much material it will take to put the proper amount on the bottom and then apply all of it.

"If it's three coats or ten coats it is the amount of material that counts," continued Seidel.

Even when correctly applied, it's likely that no repair filler or coating can fully prevent repeat blistering in a hull that has large areas of voids and unsaturated fibers in the outer skin mat layer. While a coating may last for many years, voids must be removed before you can completely eliminate the blistering process under the barrier coating. This is both painstaking and costly, a repair most owners sidestep.

There are some measures you can take to retard the blistering process. Besides water permeating an exterior coating, there are numerous ways water can get into a laminate, such as thru-hull fittings or water in the bilge.

Be sure all thru-hulls are well sealed, recaulk any leaking deck fittings. Hulls absorb a great deal of water from the interior. Keep the bilge dry, particularly areas that are not gelcoated or painted. — Jan Mundy

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THE LITMUS TEST Osmotic blisters come in many disguises.

Some are purely cosmetic, others compromise the structural integrity of the hull. Whether your boat is with or without blisters or a barrier coat, use this test to survey your boat, you might be surprised.

By H.W. Roman Folk

Testing Tools Waterproof marker Safety goggles Disposable gloves Litmus paper Sharp scraper Small grinder Hot air gun Drill with 12mm- (1/2") diameter countersink bit Plastic head mallet Magnifying glass Dental probe or thin, flexible blade knife Small paint brush Fast-curing filler ITH all the controversy and disagreement in the marine industry regarding osmotic blistering of boat hulls, most owners don't know who to believe regarding the seriousness of the problem. Is it just cosmetic or are blisters possibly an external sign of structural degradation of the laminate? Is it a problem that is easily cured by grinding and patching or is it necessary to remove laminate layers and apply new material?

Fiberglass boats built of polyester resin (most production boats) may be affected by a problem, that over a period of years, could completely degrade the laminate and eventually cause a vessel to become unseaworthy. This problem is a chemical process called resin hydrolyzation which is defined as the breakdown of cured polyester resin into its component raw materials owing to an interaction between permeating water molecules and chemicals that are normally present in polyester. Boats that are hauled for the winter and have anywhere from four to six

months to dry out, tend to suffer deep-rooted hydrolyzation to a much lesser extent than their saltwater counterparts that spend a full year in relatively high temperature water. (Be especially overcautious if you're considering buying a "bargain" boat from southern climes.)

Research has found that blisters can be caused by several agents acting singly or in various combinations. Considering the extreme range of conditions in which boats are used and the various laminate schedules, it's only logical that there isn't a single cause for osmotic blisters. So how do you determine if the blisters found are a result of damaging chemical processes?

Sounding the Hull The blister tests described below interpret what

JAN MUNDY

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LESLEY G. CAMPBELL

Blisters found at the gelcoat-laminate interface are repaired by blasting or peeling of the gelcoat, drying, filling the voids and applying a thick epoxy or vinylester barrier coat.

Small, cosmetic blisters with a neutral pH value of 7 are easily patched. Š DIY boat owner 2001 1-888-658-2628

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is occurring beneath the gelcoat. These tests measure the degree of acidity in the laminate, rather than a hull's moisture level. Readings from moisture meters may not be a true indication of the hydrolyzated state of a hull and are only truly accurate when interpreted by an experienced surveyor.

These tests require that the boat be out of the water. Clean the bottom of the boat and draw circles around all blisters with a waterproof marker. Do this the minute the boat is hauled — smaller, cosmetic blisters often disappear within a few hours. Larger, deeprooted blisters that extend into the laminate may be visible for many months after the boat comes out of the water.

While standing at the bow and then the stern, sight along the hull where it's supported by a cradle or jack stands. Look for any deflection or hollows where the hull is in contact with the supports. On sailboats, look for any concavity on the bottom where the keel intersects the hull. Does it look as if the keel is pushing up into the hull? If you think there are hollows in the hull lines, get someone else to look at the boat to see if they see the same problem. Then with your plastic mallet, tap the hull, using a steady rhythm (tap, tap, tap...) in the suspect areas. A solid laminate has a nice "ringing tone." A waterlogged core and damaged laminate beneath the surface offers a much duller sound. Mark the areas of "dull" sounds with the waterproof marker. A "soft" bottom is not always caused by a damaged laminate. Another source is laminate fatiguing and microcrazing of the resin through years of abuse as found in many older powerboats.

The Acid Test Blisters may have several reasons for developing and the following should help you determine what type or types are on your boat.

The size and location of the blisters are useful in determining the cause. However, a boat may have adjacent blisters caused by different processes. Additionally, the presence or lack of a barrier coat will determine the nature of the blistering.

Small blisters, less than 6mm (1/4"), present in a band about 15cm- to 25.4cm- (6" to 10") wide at the waterline, are often caused by algae or grass that grows on the waterline.

Parts of the organism dig into the bottom paint and gelcoat where they decompose and cause blisters to form. Another possibility is chemical pollutants floating on the surface and reacting with the bottom paint, often discoloring the

paint. Pop a few of these blisters and test the liquid content with your litmus paper. If neutral, a pH value of 7, or nearly so, means they are cosmetic and easily patched.

Interface blisters are those that form between the gelcoat and the first laminate layer.

Uncured resin, excess hardener or air-filled voids allow water to concentrate and become an acidic solution, potentially dissolving the surrounding resin (hydrolysis). Fluid in these nearly always has a pungent, rotten odor and may be under considerable pressure — wear goggles when breaking the blisters. The fluid will be slightly acidic, somewhere between 4 pH and 6 pH. Interface blister cavities usually have a tiny hole in the bottom. When opened, a larger cavity will be found. If the blister is of the interface type, this cavity will have smooth, solid sides. Always wear safety goggles when working on blisters, as some when punctured can emit a high-pressure stream of liquid that may be extremely corrosive.

Close-up Survey To perform the next tests, the original laminate must be examined. You will need to scrape or sand away sufficient antifouling paint to determine if the boat has been previously barrier coated. Select two or three spots on each side, just above the keel and under the cockpit should be sufficient. A small grinder saves a bit of labor at this point.

If your boat has been barrier coated, spot patched or is an older boat that has never shown blisters, don't think that all is hunky-dory.

If your boat has no blisters, at each spot where you have exposed the original laminate, drill a hole with the countersink bit — don't drill all the way through. Examine each hole with the magnifying glass. Can you see dark spots? Is liquid seeping out of the layers? Are layers separated? Is the resin soft or spongy? The pH readings on any such damaged area will invariably be quite acidic. If no liquid seeps from the drilled area within 30 minutes, the area around the hole may be gently heated or left overnight and examined the next day. The change in temperature will normally cause some liquid to appear on the surface.

Where there is a barrier coat with visible blisters, open the blisters and test the fluid with litmus paper. Neutral (pH 7) or alkaline (pH 8 or higher) readings are normally a sign that the barrier coat didn't cure properly. Acidic readings are a sure sign that the laminate is affected by resin hydrolyzation and is being degraded. © DIY boat owner 2001 1-888-658-2628

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It's not unusual to find adjacent blisters with different pH readings. If the blisters are scattered over the surface of the hull, open several of them. Use a Dremel, a variablespeed, hobby-type die grinder with a 5mm (3/16") diameter round-tipped rotary file to open blister holes. Examine the surface in every exposed blister cavity. Quite often a tiny hole can be seen as with the interface blisters. Use the countersink bit to drill into the laminate at this point. Examine the sides of the hole with the magnifying glass while gently probing with the dental probe. Are laminate layers easily pulled apart or are they already separated? If the hole is dry, wet your paint brush with clean water. Gently heat the area around the hole. If any liquid is seen seeping from the newly exposed laminates, test with the litmus paper.

Use the brush to push a strip into the hole, if necessary. An acidic reaction at this point is not a good sign. The strong acid and separated layers are positive signs that the laminate is being affected by resin hydrolyzation.

Caution: Be extremely cautious when heating fiberglass. A paint-stripper-style gun releases enough heat to cause heat damage to the laminate even to the extent of causing trapped solvent to flash off. Also, around 45°C (150°F) many coatings start to soften, so an epoxy or vinylester barrier coat may be damaged.

You've scraped away bottom paint and drilled holes in the hull, now what? First, take

close-up photos of the spots with the strongest acidic readings and also of the blisters found in any recently applied barrier coats. Photos shot at greater distance can be used to document the locations of your tests. Barrier coat problems should be discussed with the applicators if you didn't perform the work, and with the manufacturer if you did it yourself. Fill all the holes and areas where you used the grinder with a quick-dry epoxy or vinylester glue or filler (i.e. 3M Marine Premium Filler, Marine-Tex), prime and paint.

If you find that resin hydrolyzation is taking place within the laminate of your hull, there is, arguably, not much you can do about curing the problem. It's a costly repair if contracted out and a massive job for the do-it-yourselfer, although, not unworkable. One of the oldest fiberglass boats surveyed by Ontario-based surveyor Jonathan Watson was a powerboat built in 1952. The bottom had gone "soft" due to a combination of fatiguing and a certain amount of resin hydrolyzation. This boat was successfully rebuilt by removing the damaged laminate layers and relaminating.

Blister repair methods and materials have greatly improved and can repair all but the most severely hydrolyzed hulls. Proper preparation of the hull — removing all damaged laminate, thoroughly drying the hull and correct application of a barrier coating — is the key to a successful, long-lasting blister repair.

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HOW DRY IS DRY? HE moisture content of fiberglass must be reduced to an acceptably low level but determining this level can be a problem. The Interlux bulletin suggests taping a 30cm (12”) square of clear plastic to the hull, sealing all edges with tape and leaving it for at least 24 hours. If condensation forms under the plastic, the hull requires further drying. When this test produces a dry inner surface, the boat is probably ready for coating. A moisture meter

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provides a semi-accurate reading, but it’s expensive and interpretation is questionable.

(See When is the Hull Dry Enough? on page 8.) In areas where the harsh winters dictate six months or more in dry dock, there’s probably sufficient time to achieve a dry hull. (Use the plastic patch test to double check.) If you are unsure, a surveyor can provide valuable advice.

—Jan Mundy

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WHEN IS A HULL DRY ENOUGH? moisture meter serves two purposes in blister repairs: to assess the moisture content of a laminate, and to determine when the laminate is dry enough to be recoated. It’s an important tool that lets you diagnose the problem, but it may not be a true indication of a hull’s wetness.

Moisture levels at which blistering occurs vary from boat to boat. A boat identified by the moisture meter as being very wet may have no visible symptoms, while another boat that meters reasonably dry may have a severe case of the pox. Moisture content can also vary over a very small area, because polyester laminates absorb moisture unevenly. The depth to which a meter can detect moisture also affects the readings; some meters may not detect the wetter layers underneath.

When the Regal I repaired was metered soon after sandblasting, the hull above the waterline read 5% on the meter, and anywhere from 18% to 25% — or approximately 2% moisture by weight — on the bottom. (A soaking-wet hull might contain 3.5% moisture by weight.)

The bottom was metered at regular intervals throughout the winter and numbers written on the hull. By spring, the hull had held at 18%.

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Because of the random readings, I called in a surveyor. As the moisture content had stabilized, the surveyor confirmed that it was reasonably safe to coat as the laminate was as dry as it was going to get.

So how do determine when the hull is ready for coating? If you have any doubts as to the “dryness” of the hull, call in a surveyor. When readings are questionable, the only truly accurate means to determine the exact moisture content is to remove a hull core sample and send it to a lab for testing.

— Ken Hendry

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WHEN YOU NEED TO REMOVE... removing bottom paint or fiberglass for osmosis repairs, an alternative to sand or baking-soda blasting, grinding, disc sanding or chemical paint removers is to have the surface peeled.

This method involves removing a controlled amount of material using a tool that resembles a hand-held power planer. In one pass, the “peeler” cuts a 10cm- (4"-) wide slice of a predetermined thickness.

It can remove bottom paints, topside paints, varnish, epoxy and fiberglass laminates.

I watched as Claire Dumouchelle of Clare’s Mobile Marine (519/734-7043 or claresmobile@ hotmail.com), removed the outer laminate below the waterline for an osmosis repair on a 5.4m (18') runabout. Two hours later, the job was completed without any mess or dust (all residue is collected in a Shop Vac). The resulting finish was impressive — an even, smooth surface that requires only light sanding and degreasing before recoating or repair. No filling or fairing. Powerboats with strakes take longer and these areas need to be hand finished, while smooth-hulled sailboats are apparently easier and faster.

Peeling is expensive: price per foot for powerboats up to 9m (30') in length is $25 and $23 for sailboats up to $40 for 50footers. But when you factor in clean-up time, labor and materials for filling and fairing, it likely saves money and time in the long run.

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Except some hand fairing at the strakes, peeler leaves an even, smooth surface, ready for recoating or repair.

— Jan Mundy

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POWER STRIPPING a badly blistered hull involves removing the bottom paint, gelcoat and often several layers of laminate, a task that is simplified by using a Porter-Cable model 7403 Paint Remover A heavy-duty paint and gelcoat stripper it features a 15cm (6”) diameter 36-grit tungsten carbide disc that uniformly “shaves” the surface. A special plate attachment lets you adjust the depth of the cut to remove an even amount of material and leave a fair, smooth surface for coating with epoxy. This stripper will generate a large quantity of dust so you’ll need to wear protective clothing, gloves, goggles and a respirator. If you presently own a Porter-Cable model 7402 vertical disc sander, you can purchase the bottom attachment, backup pad and hardware separately.

—Jan Mundy

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E PAIRING

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BOTTOM PAINT REMOVAL is a twocomponent system that removes multiple coats of antifouling paint from fiberglass, wood, steel, aluminum. Manufactured by Dumond Chemicals, (1501 Broadway, New York, NY 10036; Tel: (212) 8696350), it contains no methylene chloride and will not harm gelcoat. It's available in two formulations: Peel-Away Marine Safety Strip for most applications and Peel-Away II for boats coated with an epoxy primer or barrier coat. The manufacturer recommends first doing a test patch when the coating type is unknown.

It removes up to 10 coats, often in a single application.

Last spring (1995) we attended a demonstration conducted by Tom Pollock of Payne Distributors, the Canadian wholesaler. The test boat was an old steel hulk layered with multiple coats of some unknown bottom paint.

Applying Peel-Away is similar to wallpapering. A nonsagging paste with a consistency like mayonnaise coats the bottom paint and then is covered with strips of plastic-coated paper. The paper seals the paste and prevents evaporation.

Peel Away's only drawback is time. Depending on the thickness of paint and outside temperature, it takes 12 to 48 hours before you can remove the paper and scrape the surface. While it's more expensive than sandpaper or discs, it's a lot less strenuous and definitely less hazardous to your health.

Albeit it's a relatively safe product (contains no solvents),

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you should wear protective clothing and gloves and work is a well-ventilated area.

Optimum working temperature is 15.5 C (60 F); below 7 C (45 F) the product becomes dormant.

Cost to strip a 7.5m (25') boat using the standard PeelAway product averages $250. Coverage is 40 to 50 square feet per 3.785L (1 US gallon).

Remove any flaking or peeling paint with a wire brush. Apply a thick coating of paste, about .3cm to .5cm (1/8" to 3/16"), with a large brush. Work in .9 sq.m (3 sq. ft.) sections, covering all traces of bottom paint. Protect painted bootstripes with a solvent-resistant striping tape.

Cut laminated cloth into small strips (especially on a windy day) and cover paste with the printed side facing out. Lightly press surface with hand or a roller. Trim edges, allowing about .6cm (1/4") overhang. Wait 12 to 48 hours, depending on the thickness of the coating.

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C HECK a small area to test if ready. Slide a large paint scraper under the fabric and ease paste, paint and cloth away from the surface in one piece. Scrape excess paste with putty knife, being careful not to scratch the hull.

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Remove all remaining residue with water and a 3M Scotch Brite pad. Do not let the paste dry as it hardens and will require sanding.

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A single application removed all paint on our test area. —Jan Mundy

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FAST REMOVAL OF BOTTOM PAINTS Blasting antifouling paints away with non-toxic baking soda is an effective, non-abrasive alternative to sanding, grinding or applying chemical strippers.

By Don Campbell

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LESLEY G. CAMPBELL

FTER completing extensive repairs on the delaminated deck of our '74 vintage Alberg 30, White Opal, [see "Replacing a Soggy Deck," DIY 1998-#2 issue — Ed], our next step was to paint the bottom. After years of adding layers of sloughing antifouling paints, the surface was anything but smooth, which surely affected the boat's performance. Friends had warned me that manual removal of bottom paints, by either sanding, grinding or scraping, was an arduous chore, painstakingly slow and not particularly healthy because of the amount of copper (cuprous oxide) contained in the material being removed. I considered sand blasting which cuts through the paint fast but can damage the surface resulting in hours of filling and fairing. In my search for an alternative, I discovered the Armex Accustrip System, a very passive blasting method that

uses baking-soda crystals. It's a highly effective solution to removing paint.

The process of applying baking soda is similar to sandblasting. A high-volume, highpressure air compressor is used to propel baking soda (sodium bicarbonate) from a metering system to a nozzle that allows the operator to direct the flow to the surface to be cleaned. It's the same baking soda used in the kitchen but the crystals are much larger, about 170 microns in diameter I'm told, and while this is still small, it's very adequate for the job at hand. (A micron is 1/1,000 of a millimeter or about 1/25,000 of an inch.)

Before: Years of applying sloughing-off, soft bottom paints have left a rough, bumpy surface.

After: Baking-soda blasting followed by a freshwater rinse leaves the hull ready for a finish sanding.

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LESLEY G. CAMPBELL

The author sanding with a random orbital sander and 80-grit paper to remove minute traces of bottom paint and smooth over blisters.

Applying Interlux Watertite fairing compound.

The velocity of the crystals passing through the nozzle can be varied depending on the surface material. For gelcoat removal, velocities of 720 km-h (450 mph) are often used. The energy to remove the paint comes from the crystal shattering rather than any abrasive action from the blasting process.

Because of this, there is no scratching or roughing of the gelcoat, so the job is very kind to the surface. In fact, the particles are gentle enough to remove paint from an empty pop tin without denting the aluminum! Voids or osmotic blistering will break open and any liquid will be expelled.

The contractor I hired inquired about the available space at the boat site and surroundings. Because the boat was stored on a trailer at our farm, with no close neighbors, no shrouding, drop cloths or extra precautions were necessary.

The application of sodium bicarbonate will change the pH in the soil, giving a faster neutralizing reaction than the application of calcium carbonate (lime).

Actual blasting of the 23.5sq.m (253sq.') area was completed in 2-1/2 hours, which allowed me to begin sanding the same afternoon. About 70kg (150lb) of baking soda was used. There was so little residue in any one place under the trailer that none

could be scraped off the gravel driveway.

Some of the grass along the edge of the driveway did die but this was probably from copper toxicity rather than the sodium bicarbonate. The flow of bicarbonate at the end of the nozzle was so light that one could not see any color change of the background due to white crystals coming out the nozzle.

The only noticeable reaction was the receding paint line as the material was directed at the hull. The waterline paint had also been layered and as much of this as possible was removed by blasting; not a perfect job, but made sanding a muchreduced effort.

This process is useful for any cleaning application that requires gentle handling or restoration of virtually any surface.

Drawbacks of the process are few. If wooden blocks support depth gauge transducers, they will be eaten away by the process, the softer grain in the wood first. And certain epoxy coatings (i.e. Interlux 2000) are difficult to remove. When weighed against the benefits, namely speed and quality of the final finished surface, the payoff is worth the cost.

Preparation is minimal; whether you're sanding, grinding or blasting, the dust that coats surroundings must be confined, especially in marinas.

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INTERLUX

DRYING TECHNIQUES

the area with detergent and flush out with freshwater to remove any contaminants. Allow the area to dry to remove all moisture from the bottom. Drying could take anywhere from two weeks to two months or possibly longer depending on the severity of the blistering. The more blistering, the more water the hull has retained. Removing all of the moisture from the hull prior to repairing and recoating will minimize the possibility of blisters reoccurring. Infrared heat lamps or tenting the hull area with plastic sheeting will speed up the drying process. In the latter case, wrap the bottom in plastic, held in place above the waterline with tape and weighted at the bottom to form a tight seal. Dehumidifiers and small fans to keep the air moving are placed inside the tent. Keep the bilge dry and well ventilated to prevent moisture from entering the laminate from the inside. If the boat is stored

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A simple method to determine hull dryness is to tape squares of clear plastic sheet over the surface.

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inside, use heaters or fans to force dry the surface.

Check the moisture content of the fiberglass laminate with a moisture meter before applying any coating. Test the hull both above and below the waterline in several areas every two to three feet apart. Mark the spots on the hull where you take the readings and every few weeks again check the moisture content. A meter reading of 2% or 3% is recommended. Another method to determine hull dryness is to lay 30.4cm (12") squares of clear plastic sheet over the surface and seal all edges with tape. Leave for at least 24 hours. If condensation forms, the hull requires further drying. Remove the plastic, wipe the area and plastic dry and repeat until the plastic remains dry. —Jan Mundy

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ESTIMATING COVERAGE USE the following formulas to calculate the square footage

of the underwater area when estimating coverage of epoxy-based coatings and antifouling paints:

For displacement powerboats and full-keel sailboats Beam + draft x LWL (waterline length) = square footage Planing powerboats and modified-keel sailboats Beam + draft x LWL x .75 = square footage Fin-keel sailboats Beam + draft x LWL x .50 = square footage

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REPAIR TECHNIQUES the gelcoat from moisture with an epoxy-based coating helps to prevent osmosis. If your boat develops small and shallow blisters you can repair it yourself. The best time to spot blisters is when the boat is first hauled out of the water. Immediately mark the blisters with a waterproof pen. Blisters may begin to disappear within a few hours but will reabsorb water when the boat is launched.

Osmosis may not be evident under several coats of antifouling. Scraping or sanding may reveal bumps or crescent-shaped cracks from the size of a match head to a quarter. Before beginning to remove the antifouling paint, wash and clean the hull area being repaired.

Removing all of the surface contaminants — marine growths such as algae, barnacles, sea grass, etc. — is the first thing that needs to be done. Use an acid-based cleaner to quickly dissolve any growth and grime.

Next, remove the bottom paint from the affected areas using a 24- to 36- grit abrasive.

This should take off 60% to 70% of the bottom paint. Some abrasives are specifically designed for this process. They utilize a special coating process to prevent them from loading on soft bottom paints and fairing compounds and give an increased cut rate. Use a finer grit (60 to 100) to remove the remaining coating.

Make sure you take the proper safety precautions before sanding. When removing bottom paint or sanding fiberglass and gelcoat always wear protective clothing, gloves and a face respirator. Some manufacturers do not recommend using chemical paint strippers to remove bottom paints. Such products facilitate paint removal but may damage gelcoat or the polyester resin in the laminate. Another option is to use Peel Away, a non-methylene-chloride stripper that removes multiple bottom paint coatings from fiberglass, wood, steel, aluminum (see product demo on page 11).

Where a bottom has small, isolated blisters it is not necessary to remove the gelcoat. Clean the surface with a dewaxer or solvent wash. Open each blister individually then fill and fair the blister cavities followed by an epoxy coating. Use a countersink bit on a variable-speed drill to open blisters. Wear protective clothing and eye protection (goggles EALING

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Sandblasting removes gelcoat and opens blister cavities but must be done by a competent operator.

or full face shield). The acidic fluid may be under as much as 200 psi of pressure.

If the bottom is covered with small or large blisters that go into the laminate, you'll need to remove the gelcoat surface down to the fiberglass laminate and at least 5cm (2") above the waterline. This is accomplished by either sandblasting, peeling or grinding.

9 1 2 3 4 5 6 7 8 9

Steps to Blister Repair

Wash and clean area Remove bottom paint Remove gelcoat Expose and clean blister area Dry out hull Seal repair area Fill and fair repair area Apply barrier coats Apply primer and antifouling paint

Sandblasting with sand or other mediums will remove the gelcoat and open any blister cavities but must be done by a competent operator — in the wrong hands, sandblasting can blast a hole right through the laminate. It's effective but can embed particles in the laminate and leave a bumpy finishGelcoat peeling is the most efficient method of removing gelcoat. It leaves a clean, smooth surface, but because it requires expensive hand-held or robotic equipment, must be done by a contractor. Grinding is painstaking slow and messy work but the most common solution for do-it-yourselfers.

Use a grinder fitted with a soft back-up pad and 24- to 36 grit discs and grind until you © DIY boat owner 2001 1-888-658-2628

16

INTERLUX 3M

A simple method to determine hull dryness is to tape squares of clear plastic sheet over the surface.

Use a grinder with a foam disc pad to remove bottom paint.

tenting the hull area with plastic sheeting will speed up the drying process. In the latter case, wrap the bottom in plastic, held in place above the waterline with tape and weighted at the bottom to form a tight seal. Dehumidifiers and small fans to keep the air moving are placed inside the tent. Keep the bilge dry and well ventilated to prevent moisture from entering the laminate from the inside. If the boat is stored inside, use heaters or fans to force dry the surface. Check the moisture content of the fiberglass laminate with a moisture meter before applying any coating. Test the hull both above and below the waterline in several areas every two to three feet apart. Mark the

JAN MUNDY

reach the laminate layer. Hold the grinder at a low angle to avoid gouges. Be careful not to cut into the laminate. Often grinding removes all blistering occurring between the gelcoat and skin coat, the first layer of mat. If you canstill see light-colored circles of delamination, you'll need to remove the damaged laminate. Using a 7.6cm (3") 24- or 36- grit grinding disc on a drill attachment, grind out the contaminated laminate area, forming small craters until all signs of delamination are removed. Gougeon Brothers recommend "sounding" the hull with a rubber mallet to detect any laminate degradation. Wet or delaminated areas will sound dull or flat; Damage can range from a few small blisters to an entire hull dotted with the "pox." dry, solid laminate has a sharp sound. If there is evidence of delamination or blistering spots on the hull where you take the readings above the waterline consult a surveyor. and every few weeks again check the moisture Scrub the area with detergent and flush out content. A meter reading of 2% or 3% is with freshwater to remove any contaminants. recommended. Another method to determine Allow the area to dry to remove all moisture hull dryness is to lay 30.4cm (12") squares of from the bottom. Drying could take anywhere clear plastic sheet over the surface and seal all from two weeks to two months or possibly edges with tape. Leave for at least 24 hours. If longer depending on the severity of the condensation forms, the hull requires further blistering. The more blistering, the more water drying. Remove the plastic, wipe the area and the hull has retained. Removing all of the plastic dry and repeat until the plastic remains moisture from the hull prior to repairing and dry. recoating will minimize the possibility of When thoroughly dry, wash the bottom blisters reoccurring. Infrared heat lamps or again with freshwater. Scrub the surface with a Š DIY boat owner 2001 1-888-658-2628

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Š DIY boat owner 2001 1-888-658-2628

INTERLUX

3M Scotch Brite pad to remove any surface contaminates leached out during drying such as glycol, a liquid component of polyester resins that unlike water, does not evaporate.

Some manufacturers recommend pressure washing the hull with hot freshwater every three to four weeks during the drying processing to remove all glycol contained in the laminate. When the Multiple coats of Interprotect or other barrier coating are applied after surface has thoroughly filling the blisters and fairing the surface. dried, apply a sealer coat to cover the followed by 180 grit to refine the surface for exposed laminate surfaces. These sealers are typically low viscosity epoxy coatings designed painting. Follow manufacturer's instructions for finishing details. to seal voids and pin holes prior to applying a Multiple coats of a recommended epoxy fairing compound and barrier coatings. Follow the manufacturer's directions. Epoxy coatings developed for blister repair include many DIY Repair Bill epoxy resin systems (West Systems, East Epoxy and others), Interlux's Interprotect System and Approximate cost for repairing a 7.8m (26') Sikkens Epoxy GP System. sailboat covered with small blisters. In this The surface is now ready for fairing. example, sandblasting was not necessary.

Fairing is the process of making the surface flat Prices vary depending on the blister repair and smooth again. Any surface bumps or product used. Professional yards charge about dents in the hull will result in a decrease in $100 per foot (LOA) for a complete blister performance and appearance. Apply the repair. Estimates for DIYers run about $60 per fairing compound to fill the exposed cavities. foot.

Use large putty knives and battens to apply a smooth layer of filler. Several thin coats are Dewaxer $50 better than one thick coat. Don't use a Fairing compound $200 polyester fairing compound below the Epoxy coating $350 waterline. Epoxy or vinylester work best here.

Anti-fouling primer (1 coat) $90 Again, follow the manufacturer's instructions.

Anti-fouling paint (2 coats) $280 When dry, sand off high spots, remove dust Rollers, sandpaper, discs, brushes, solvent and refill low spots. Be sure there are no $100 pinholes or glass strands protruding through TOTAL $1,070 the filler.

Once the fairing compound material has dried, proceed to sand or "rough shape" with barrier coating followed by a primer and 36-grit sandpaper or disc to knock down the antifouling paint are now applied according to material quickly. Don't sand too much or you manufacturer's instructions at this time. Wash will have to apply more fairing compound to the hull with the recommended solvent before your low spots. Finish sanding with 80 grit applying primer.

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CAVITY TREATMENT I hauled a customer’s 1984 8.1m (27’) Regal cruiser last fall, I found that it had developed many small blisters spread all over the bottom. The hull was coated with a bottom wax which like antifouling paint, had to be removed before any blister repair could begin. In the early stages, blistering occurs directly under the gelcoat and the repair is straightforward. Where there are only a few small blisters, these can be opened up individually using a grinder without removing the gelcoat on the rest of the hull. If the bottom is covered with larger blisters, or where you suspect the blisters may go into the laminate, the entire gelcoat layer must be removed by grinding or sanding, which is painstakingly slow and messy work, or blasting with baking soda or sand.

Blister cavities are very difficult to find — grinding often misses spots that are covered with a thin veneer — and any missed areas will reblister after treatment. The Regal had 20% to 30% blister coverage, and to alleviate concerns about the “wetness” of the laminate, the decision was made to have the hull sandblasted. Blasting tends to find blisters and weak areas that are not yet visible.

Sandblasting must be done by a qualified operator; in unskilled hands, the process can blast a hole right through the laminate. (The Armex Accustrip system, which uses a baking soda-based abrasive, is a more passive process and does less damage to the hull.) To prepare for sandblasting, tape the waterline and lay drop cloths everywhere. Be prepared for a lot of fiberglass dust. The operator will put heavy tape over other areas that must be protected rom the sand. Block the boat high enough so there’s reasonable access underneath and you’ll get a better job. Keep the area where blocks contact the hull to a minimum to avoid the need to hand sand later.

W

HEN

Invest in a garage creeper (the kind automotive mechanics use) and be prepared to spend lots of hours on your back.

After sandblasting, immediately remove the tape, otherwise it seems to grow into the fiberglass. If sandblasting reveals more blistering and a saturated laminate, or signs of delamination which may affect the structural integrity of the hull, you’ll need to decide whether to remove additional layers. This is a drastic step; before you go that route, seek advice from a qualified marine surveyor.

I used a Dremel, a variable- speed hobbytype die grinder, with a 5mm (3/16”) diameter round-tipped rotary file, to open up the blister holes uncovered by blasting the Regal’s hull. If the hole was shallow, we did not further abrade it; when the void had penetrated the laminate, however, we widened it and cleaned it out.

Fortunately, most of the blister holes were shallow and the Dremel penetrated no more than its diameter and about the same width. Be prepared to spend lots of hours on your back.

An automotive garage creeper is invaluable if the boat is high enough. Wear protective clothing and eye protection when popping the acidic fluid-filled blisters. After opening all the cavities — again, make sure you get them all — rinse the hull with detergent and fresh water (preferably hot) to remove any contaminants.

The Regal was stored in a dry shed for the winter with all hatches and ports open to allow air to circulate through the boat. During the dryout period, the hull is rinsed occasionally with water to dissolve the glycols, a liquid component of polyester resins that, unlike water, does not evaporate.

—Ken Hendry

© DIY boat owner 2001 1-888-658-2628

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FINAL SANDING sanding was necessary to remove all traces of old paint and small blisters, taking about 10 hours each side with 80and 120-grit paper plus another four hours sanding the waterline. Sanding time will vary with the surface conditions, osmosis damage and desired finish. Use extra care when working among heavy metals like copper. Wear plastic gloves, a suitable respirator with proper filters, and coveralls sealed at the neck and cuffs. Wash work clothes separately from other laundry.

Fairing was done using Interlux Watertite (a fast-cure, two-part epoxy fairing compound) then the waterline was taped with 3M Long Mask and the hull coated with VC Tar then VC 17 antifouling paint. I found that Crown-Meakins 5mm foam rollers lasted twice as long as Simms brand with the VC products. Interlux recommends non-foam rollers for the job, but I found that foam rollers gave a very even surface for the VC Tar. Application time was relatively quick once the weather cooperated. You don't want rain on these products while curing, so I waited for good weather, which meant the painting was completed over three weeks. The waterline was then taped and finished with three coats of Sikkens yacht paint. Total time spent was 50 hours over five weeks.

F

INAL

DIY REPAIR BILL The following is the cost to refinish the bottom of a full-keeled sailboat with a length of 6.9m (22'8"), draft of 1.27m (50") and 2.13m (7') beam at the waterline.

Blasting

$800

VC products

$500

Sikkens paint

$40

Rollers, sandpaper, tape, brushes, fairing compound

$150

Total

$1490

Notes: Cleaning several boats at one site at one time will lessen the cost per boat with most contractors. Add drop cloths to the above cost if cleanup is necessary.

Check with the contractor to see if they have past experience with the surface to be cleaned. Do not blast off copper paints near a garden and be considerate of other's property within marinas and boatyards.

Š DIY boat owner 2001 1-888-658-2628

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BLISTER REPAIR TECHNIQUES In this article, an expert shares some of his repair techniques and tips.

By Ken Hendry

have just hauled out the family boat and while washing the hull you notice small round bumps all over the bottom. Some are the size of a pencil eraser, while others are larger and a few have a crack in the middle. On some spots the outer layer of gelcoat has flaked off exposing a dark-colored laminate underneath.

Many boaters now recognize these spots as blisters, caused by moisture migrating through the fiberglass and accumulating in cavities that fill with an acid-like fluid. Blister repair has developed from a trial-and-error process to a fairly well understood operation with a good likelihood of success. For now, the best protection against blistering is to apply one of the various waterproof epoxy barrier coatings developed for this purpose. Such products are available from Easy Epoxy, Interlux, Jotun, Matrix Adhesive System, Sikkens, West System and other suppliers. Most are made for do-ityourself application and come with step-by-step instructions.

OU

Y

Applying Interlux Products One of the most popular products, the Interprotect System by Interlux, has been used for many years as both a preventive measure and repair method. It consists of an epoxy sealer, a fairing compound and an easily applied coating that can be put on in a relatively short time. Before starting, obtain a copy of Interlux’s Technical Bulletin #900C (call 800/INTRLUX to order). The company also has a handy question-and-answer INTERFAX service (dial 800/685-7151) that will provide you with complete painting specifications for your boat.

3-Step Application Once you’ve opened up the blisters and dried out the hull, the first step in the Interprotect system is to apply Interlux 1000, a low-viscosity, two-part epoxy resin. It brushes on and seals blisters and any bare laminate as well as

providing a base for Interprotect 2000 (or 3000 spray formulation). Where the blisters are scant, the Interprotect 1000 can be applied directly to the cavities only. If there are a lot of holes and exposed bare laminate, however, the entire bottom must be sealed. It’s important that no fiberglass strands extend through the sealer as these will provide a direct conduit for water incursion. Follow the manufacturer’s instructions carefully; the epoxy pot life is short, typically 20 minutes for the 1000 and temperature is important — on a hot day you will have less working time. Working with epoxy isn’t difficult but it is exacting. (Gougeon Brothers (517/6847286) publish two excellent reference manuals on blister repair and epoxy techniques.)

Next two or more applications of Interlux 417/418 filler are worked into the blister

Fill pinholes with fairing compound and a putty knife held at a low angle.

cavities. Use a squeegee or putty knife wider than the holes. Again, watch the pot life and mix only small amounts at a time. A trick I use is to work in small areas, sealing with 1000 and, soon after, applying the filler while the sealer is still “green.” After the first area is filled the next area can be coated with sealer, filled and so on. Once the epoxy hardens beyond the “dent with fingernail stage” — after standing © DIY boat owner 2001 1-888-658-2628

21

approximately eight hours in 20C (68F) daytime temperatures or overnight at the 10C (50F) temperatures I had during the Regal repair — the surface must be scrubbed with a 3M Scotch-Brite pad and water to remove the amine blush (a by-product of epoxy resin), then sanded with 80-grit paper and wiped with solvent. So watch the overcoat times and plan your sealer and filling times carefully.

When the filler coat is dry, thoroughly sand the hull to remove any high spots. Bright lights directed along the bottom will reveal any low spots; they show up as shiny areas and require a second application of filler. (A tip: when you use lots of filler sanding may be more time consuming, but you can also avoid refilling.)

Finish sanding with 80-grit paper.

The next stage is the application of multiple coats of the Interprotect 2000. Vacuum the work area to remove all dust residue, then wash the bottom with solvent. Mask the waterline using 3M Long Mask or another quality weather-resistant tape. Following the manufacturer’s instructions, mix up a batch of 2000 and let it stand for 20 minutes beforeusing it. Five to six coats are applied with solvent-resistant foam rollers (the product goes on like paint) , but these will start to come apart after a few hours, so plan on at least one roller per coat. Wear protective clothing and a paint/solvent respirator when working with epoxies or paints.

When you’re finished, your coats of 2000 should be 10 mils or 0.010 inches thick. A nifty way to measure thickness is to paint the same number of coats “wet on wet” on a piece of tape, then determine the thickness of the tape using a caliper, with and without the 2000. For example, the tape used on the Regal measured 0.006, so we applied successive coats until the surface measured 0.016. The label on the 2000 can also provide information about the

Interprotect 2000 is rolled over a smooth, fair hull surface.

number of coats and their thickness.

Interlux specifies four to 18 hours curing time between coats, depending on the temperature of the hull, after which resanding is necessary — and you do not want to sand this thing again. The minimum times are to permit complete vaporization of the solvents in the 2000. Trapping solvents with a second coat is just about as damaging as water left in the laminate.

Epoxy coatings are not UV resistant and must be overcoated with an antifouling paint.

Interprotect 2000 has the advantage over other epoxy brands as it can be overcoated with Interlux Fiberglass Bottomkote, or another compatible bottom paint within a few hours of applying the last coat without resanding — and we’ll do anything to prevent having to go over the bottom again.

When properly applied, an epoxy barrier coating provides long-lasting protection.

Occasionally, however, osmosis can restart and blistering reoccurs within a few seasons. This happens when the hydrolyzed wet laminate is not completely removed, or inadequate hull preparation results in poor adhesion between the epoxy barrier coat and the substrate. Should blisters reform, repair as necessary on a spot basis and then recoat as before.

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EPOXY Epoxy resins are the most widely used for repairing osmotic blisters. Here's everything you need to know to ensure a successful job, including a summary of material costs, daily scheduling, reasons for failure and prevention tips.

Story and photos by Jim Shotwell

boat buddy, Melvin Howard, a retired Baltimore City police officer, called with the bad news. During a routine bottom cleaning of his '78 Irwin 37 center-cockpit sloop the diver discovered blisters, lots of them.

After much consideration I decided to do the repair job for him to insure it was done to the highest standards, not to mention saving him money. The one condition: he was to assist me.

The going rate for gelcoat blister repair on the upper western shore of Chesapeake Bay, where Princess II is berthed, often exceeds $100 per foot of boat length.

Much has been written about the causes of gelcoat blisters. Princess II had last been hauled and surveyed in '94 and showed no signs of blisters. It's believed that boats that stay in the water year-round are more prone to blistering than those that are hauled and stored on the hard for part of the year. Was this the cause of the problem? Maybe, but that was of little concern as our only objective was to return the structural integrity to the hull.

I've built wood-epoxy boats for more than a decade and chose MAS Epoxies from Phoenix Resins for this job because of the success I've experienced with the product and the company's technical support. The repair procedures outlined below are easily adapted to most epoxy systems — East, Epiglass, System

M

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3, West and others — and involve sandblasting, drying the hull, filling, fairing and recoating the bottom according to the manufacturer's instructions.

Step 1

The Site

We needed a site that allowed owner do-ityourself projects, had the travel lift capabilities, space to work and a management philosophy based on teamwork. Marinas willing to cooperate with DIYers are becoming scarce. Last October we moved the boat to Bowley's Marina at the mouth of Middle River in upper Chesapeake Bay. It was hauled, power washed and blocked in the sandblast area. A 500-slip facility with a 30-ton Travelift, a large work yard, a sandblast area and friendly knowledgeable staff, Bowley's is boatyard heaven.

Step 2 Sandblasting and Sanding Antifouling paint must be removed and the blisters opened to allow them to dry out before repairs can begin. Princess II was sandblasted for three reasons: to remove the bottom paint; to open the blisters; and to "tooth up" the gelcoat in preparation for the epoxy coating.

Sanding and grinding or chemical stripping and sanding will also get the job done, but are more labor intensive and consequently more

SAFETY TIPS – Always!

• Always read all product labels before opening.

• Always wear safety glasses, disposable gloves and protective clothing.

• Always have good ventilation.

• Always use a respirator with an organic vapor cartridge when sanding epoxy.

• Always clean spills on skin (or clothing) with white vinegar, then soap and water.

• Always wash thoroughly after working with epoxy, especially before eating or smoking.

• Always call a physician in case of ingestion.

After sandblasting, the extent of Princess II's blistering became obvious. © DIY boat owner 2001 1-888-658-2628

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TIP: MASKING EPOXY If you want a crisp mating line, always tape with 3M 2090 Long-Mask and use two tapes; one permanent, one spare. Epoxy resins don't adversely affect the acrylic adhesive in this tape when wet, but curing generates heat and when fully cured the tape slivers where epoxy has overlapped the tape and becomes part of the lay-up. Rather than remove the tape before it cures, losing your line and recreating it another day, first tape the line, then apply a second tape directly over. When you're done for the day, remove only the top tape.

Continue laying a second tape over the first and removing it as needed.

method to determine hull dryness is to lay 30.4cm (1') squares of clear plastic sheet over the surface and seal all edges with tape. Leave for at least 24 hours. If condensation forms, the hull requires further drying.

Step 4 Washdown In the spring we washed the bottom with a stiff brush and water to remove the contaminants

Princess II's owner removes contaminants from the drying process with a stiff brush.

The author uses a clean rag and denatured alcohol to remove the last of the contaminants.

costly. Sandblasting opened the blisters and created the toothed surface we needed; it's best left to someone who specializes in the process. After blasting, we carefully sanded the waterline and under the jack stand pads with a random orbital sander.

Step 3 Drying Out Before filling the blister voids the hull had to be dry, so we left Princess II to passively dry over winter. It's possible to push the drying time by many methods, such as tenting the hull area with plastic sheeting and/or heating with infrared heat lamps, but the time-honored method of patience is still the best and most cost effective. Keep the bilge dry and well ventilated to prevent moisture from entering the laminate from the inside (see "Fact Versus Fiction" on page 3).

Before applying any blister repair coating, check the moisture content of the fiberglass laminate. If you have any doubts as to the dryness of the hull, call in a surveyor. When readings are questionable, the only truly accurate means to determine the exact moisture content is to remove a hull core sample and send it to a lab for testing. Another

that came to the surface in the drying process.

After the hull dries, a denatured alcohol (methyl hydrate) wipe down follows in preparation for the initial coat of epoxy. Use plenty of clean rags and change your rag often.

Step 5 Wetting Out the Hull First tape the waterline to prevent the initial coat of unthickened epoxy from fouling the Use 3M 2090 Long-Mask for a crisp mating line and two tapes when working with epoxy (see “Masking Epoxy� on top left).

boot-top stripe. I use 3M Long-Mask for most taping operations in my shop. When doing epoxy work, I recommend removing the tape at the end of each day or use the two-tape Š DIY boat owner 2001 1-888-658-2628

24

Roll on then tip off, then continue tipping until the coating is tacky to prevent sags or runs and eliminate much of the sanding.

method (see "Masking Epoxy" on page 24).

An initial coat of epoxy resin and slow hardener, unthickened, is applied to the bottom to facilitate bonding of the epoxy filler. Mix small amounts of unthickened epoxy — start with three pumps each of resin and hardener — until you get a feel for how much you can apply during its pot life.

It's important that each blister void is completely coated with this resin mixture. First roll on the epoxy, rolling in two directions, fore and aft, then up and down. Have a helper follow with a small glue brush, dabbing epoxy into any uncoated voids. Now, "tip off" the resin, smoothing the surface with a disposable foam brush. If necessary, tip the resin a second time to insure you don't have any runs or sags.

It's much less time consuming to maintain a uniform coating while the epoxy is still "green" than sand out any flaws after it cures. When the foam brush starts to drag on the surface the epoxy has cured enough not to sag. It's best to section off the hull for coating: air and surface temperatures will determine the size of the working area that you can complete without the epoxy curing prematurely. Before the epoxy is fully cured, remove the masking tape.

Add enough filler so the thickened epoxy doesn't drip off the mixing stick.

Step 6

Always wear a respirator with an organic vapor cartridge when sanding epoxy.

Filling the Blister

Voids To rebuild the surface and fill the voids left by the blisters we mixed resin and fast hardener for about one minute, then added a pre-mixed blend of 75% phenolic microballoons and 25%

milled fibers stirred to a peanut butter-like consistency.

Use a plastic squeegee or a putty knife to fill the voids. Apply pressure to force in the filler. The objective is to fill voids as flush with the outside of the gelcoat as possible to limit the amount of sanding or refilling.

Step 7 Fairing After the epoxy filler has cured to a hard state, 24 to 48 hours at 25°C (77°F), sand the surface with a random orbital sander and 40-

grit paper. Epoxy is hard stuff and with a little care you will end up with a very fair bottom.

Take your time until you get the hang of it, but most importantly, keep the sander flat to the surface and moving. Rinse the sanding residue from the boat with freshwater and allow to dry thoroughly. It may be necessary to refill some of the voids prior to the final sanding; spot fill any depressions with a putty knife.

When this application has hardened, about 24 to 48 hours at 25°C (77°F), sand the entire bottom using 80-grit paper, rinse and allow to dry overnight. After this final sanding the bottom was once again sound, fair and smooth. © DIY boat owner 2001 1-888-658-2628

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Step 8

Apply Barrier Coats

The water barrier consists of five coats of epoxy and slow hardener, each applied about

With a two-person team, roll and tip in opposite directions. Satisfied with the final finish, the boat was left to cure for seven days, and was then ready for bottom painting.

a thicker film. We applied all five coats to the starboard hull on one day, and on the port side the next day. Coats were applied "green on green," and always within the 24- to 48hour recoat window. [Ed: Recoat-ing times and mixing ratios vary with the brand of epoxy you're using; carefully follow instructions provided by the manufacturer.]

When recoating with MAS resins, use this rule of thumb: If you can leave a thumbnail imprint in the surface, you can recoat without washing (to remove the blush) or sanding.

Apply each barrier coat with a solventresistant foam roller, rolling in two directions then "levelling" with a foam brush. This results in an even surface mil thickness. Tip off each coat in the opposite direction of the last.

Remember to carefully observe each coat and tip again if needed. Pay extra attention to the final coat on each side.

Step 9 Preparing for Relaunch

Not a single run or sag in the finished barrier coat.

3-plus mils thick, building a total thickness of 15 to 20 mils (a thick gelcoat is about 30 mils, a thin one 20 mils). If time allows and you have extra material, apply more coats to gain

The barrier coat system described is compatible with all bottom-painting systems.

[Ed: For complete step-by-step bottom-painting instructions see DIY 1999-#1 issue.] I always prime epoxy, both new construction and repairs, with Interlux 404/414 Epoxy Barrier Coat, a two-part epoxy primer for above or below the waterline. It offers a high build, bright-white sanding surface for epoxy systems. On Princess II's new bottom it also doubles as the signal coat to warn future sandblasters of the barrier layer underneath.

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DIY REPAIR BILL TIME, MATERIALS, COST This type of project is controlled by the work to be accomplished in a given day rather than the clock. Some days we worked 12 hours, others only six. This is the breakdown in hours per task.

Description Sand the waterline and wash the bottom Wetting out the hull Filling the blister voids (two applications) Fairing (sanding twice) Application of the barrier coat Total

Hours 5-1/2 15-1/2 75 43 40-1/2 179-1/2

Order materials well in advance to allow control of the cost and insure availability. Epoxy resin covers approximately 500 square feet per gallon at 3mils of thickness. For coverage purposes, add the total amount of resin plus the total amount of hardener used at the appropriate mixing ratio. To determine the area of a boat's bottom from the waterline to the keel, use this basic formula:

LOA X BEAM X .85 = AREA OF BOTTOM SURFACE The Irwin 37 required the following materials: 4 gal Low-viscosity resin 1-1/2 gal Slow hardener 1/2 gal Fast epoxy hardener and accelerator 1 Calibrated resin pump 2 Calibrated hardener pump 1-1/2 gal Phenolic microballoons 2 qt Milled fibers (chopped fiberglass, 3/8" long) Note: Resin-hardener mixing ratio of MAS epoxy is 2:1

Material costs may vary according to your location and availability of suppliers. Prices are in U.S. funds.

Epoxy resin and fillers Masking tape (3M Long-Mask) Sandpaper 3" foam and 1/2" glue brushes Roller covers Denatured alcohol Disposable gloves Mixing sticks and pots Paint tray and liners

$505 13 57 27 65 15 24 18 9

Subtotal

$721

Sandblasting $10 per boat length foot

$370

Total

$1,091

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WORKING WITH EPOXY How to prepare bonding surfaces, mix and apply epoxy glue, coat and fillet — the basic steps for building or repairing most anything on your boat.

Story and photos by Jan Mundy

WHAT YOU NEED Epoxy resin Slow- and fast-cure hardener Adhesive and fairing fillers Solvent Mixing pots, Stir sticks Paint rollers & tray Cheap glue brushes in sizes 12mm - 7.6cm (1/2" - 3") Foil (or non-printed plastic bags) Putty knives, various sizes Small plastic bags C-Clamps, pipe clamps Heavy-duty stapler & staplers Wax paper & Paper towels Low-nap foam rollers with solvent-resistant core Dust mask & Goggles Disposable latex gloves Sander and sandpaper 3M Scotch Brite pad wouldn't call myself an expert with epoxy but having applied well over 50 gallons building and repairing boats and hundreds of other things, I have a lot of user experience.

A few tools and supplies, and some woodworking experience are all you need to complete the procedures outlined below. The techniques for gluing, coating and filleting are generic and apply to many brands of epoxy but you'll need to carefully follow the manufacturer's instructions when mixing and adding fillers.

For our demonstration we used Epiglass, a product developed in New Zealand and recently marketed in North America by Interlux.

We've been testing this epoxy for the past year and its advantages are many: a low viscosity resin, it flows better when coating, laminating or sheathing and performs better in lower temperatures; and phenol-free and low- odor hardeners are safer and more pleasant to use.

Like MAS and some other epoxies, Epiglass cures with little or no amine blush, a waxy by-

I

product that appears on cured epoxy surfaces.

When coating or laminating, blush-free epoxies require little or no preparation between applications.

Many users develop severe skin irritations when using epoxy resins. Protect hands with rubber gloves or a barrier cream (I use both), wear goggles and protective clothing. Always wear a dust mask when sanding cured epoxy or when adding fillers — fine fiber particles form a toxic cloud. It's also recommended that you don't eat, drink or smoke when working with epoxy.

Epoxies will adhere to most properly prepared surfaces, except PVCs and other plastics. Humidity, air temperature, proper surface preparation and application are also critical when working with epoxy resin. Too humid air, a contaminated or too cold work surface, or over- or undercatalyzed mix can reduce bond strength and the epoxy’s effectiveness as a moisture barrier. For best results, epoxy should always be applied at room temperature and never below 10°C (50°F), unless specified. As epoxy resins have no UV protection, cover all exposed areas with varnish or paint.

Mixing

◆ Mixing the glue to the proper resin-tohardener ratio is critical. Precalibrated mixing pumps make the task easier. Always mix small batches at a time and use a slow-cure hardener to increase the working time when applying in hot temperatures or gluing, coating or laminating large areas. Thoroughly mix the resin and hardener together for at least a © DIY boat owner 2001 1-888-658-2628

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minute before adding fillers. (I keep a stopwatch in the shop just to time the mix.)

Gluing

◆ Add the appropriate filler. Colloidal silica is used for most general gluing. It can be used alone or mixed with other fillers to improve sanding and smoothness. Use microfibers when bonding wood or a brown-toned wood filler when gluing naturally finished wood.

Microballons and glass microbeads are easily sanded and used for fairing putties. Begin adding the filler in small batches (I use a coffee measurer) until the desired consistency is reached. ◆ Bonded joints offer superior holding power compared to mechanically fastened joints.

A perfect joint is not required; gaps up to 3mm (1/8") shouldn't affect the structural integrity of the bond. Bonding requires a moderately thickened batch. This mixture should have the consistency of mayonnaise; it clings to vertical surfaces but peaks formed by dipping a stir stick in the thickened epoxy will fall over. The thicker the gap, the thicker the glue required. When bonding large, flat panels, the mixture should be slightly thinner with the consistency of ketchup. ◆ Sand bonding surfaces with 120-grit paper if necessary to remove any contaminants then decrease with the appropriate solvent. A two-step glue joint offers the best adhesion and prevents resin-starved joints. The first step is to "wet-out" the bonding surfaces with an application of unthickened (no

fillers) resin-hardener mixture, then apply thickened epoxy with a glue brush to both bonding surfaces. When bonding non-structural joints, you can omit the first step. ◆ Use staples, small copper nails, clamps, wedges or jigs to hold the pieces in place until the glue sets. If the job requires a lot of staples (i.e. planking on a coldmolded hull), cut plastic garden edging into 2.5cm- (1"-) wide strips and staple through it.

After the glue has cured, you just pull the plastic to remove the staples. When clamping, apply just enough pressure until a small amount squeezes out the joint. Too much pressure and you'll squeeze out the epoxy mixture, leaving gaps and weakening the joint.

Remove excess epoxy with a putty knife, then wipe clean with solvent and paper towels rather than rags, which can contaminate the surface. Once cured, any residue is easily removed with a wood file, block plane or cabinet scraper.

Coating The object of coating wood surfaces is to provide an effective moisture barrier and a smooth surface for overcoating with a UVresistant varnish or paint. Before starting any coating job, check the humidity. Many epoxies are extremely humidity sensitive, which isn't so critical when gluing as the joint isn't open to moisture, but a potential problem when coating.

If the hygrometer reads more than 70%, it’s better to postpone the job. Both the epoxy and surface to be coated should be at room temperature to minimize air bubbles and maximize penetration into the wood. Be sure to use foam rollers with solvent-resistant cores or they'll quickly disintegrate. For coating small areas, I prefer using small rollers created by cutting a 23cm (9") roller into thirds with a hacksaw. ◆ Thoroughly mix resin with hardener and pour into a roller tray covered with foil. Load the roller with the resin mixture, roll out the excess, then roll randomly over the © DIY boat owner 2001 1-888-658-2628

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surface, vigorously rolling in several directions and loading the roller with epoxy as needed to apply an even thin coat. Make sure you have no dry spots. Work quickly and if the epoxy begins to thicken ("kick off") when coating large areas, discard it and the foil tray cover, mix a new batch and apply with a fresh roller. ◆ Remove the air bubbles by "tipping" with a foam or bristle brush wiped lightly over the surface in even strokes. Apply two coats wet-onwet, recoating when the resin is just slightly tacky, then let fully cure. Remove the amine blush (if not blush-free) by washing the surface using soap and warm water with a 3M Scotch Brite Pad. Before the water evaporates, dry the surface with paper towels and sand any remaining glossy areas with 120-grit paper (I prefer wet sanding). Let the surface dry thoroughly, then apply a final coat of unthickened epoxy. If desired, add a small amount of powdered pigment, up to 5% by weight, to change the color of the epoxy as a base coat when painting. After curing, wash again, if necessary, sand and prepare the surface for final painting. Two coats are sufficient for most non-exposed interior surfaces; three or more coats are needed for exterior surfaces. The more coats you apply, the better the moisture resistance.

Constructing a Fillet Use fillets to reinforce joints, bond panels together or to form a rounded, nicely curved joint when coating or laminating. Filleting is simple to do but perfecting the technique takes some skill and best practiced on some scraps. ◆ After thoroughly mixing resin with hardener, add enough filler to make a mixture as thick as peanut butter so it will cling to vertical surfaces; peaks in the mixture should stand up. If you have lots to do, use a slow-curing epoxy. I prefer a 50:50 mixture of colloidal silica and microfibers — you get fillets that aren't dry, don't sag, are glass smooth and

require little sanding. For fillets on naturally finished wood surfaces, use a wood filler — the brown color blends nicely. Mix small batches at a time to prevent an untimely cure before completing the fillet.

Half fill a small, heavy-duty bag (such as a freezer bag), with the thickened mixture, then nick the end off one corner at a 45° angle. The opening depends on the desired fillet size: for making fillets on 12mm (1/2") plywood, cut a 6mm (1/4") opening. Apply a bead of epoxy, doing a small section at a time, putting a generous amount on the joint. Too little epoxy and you'll have gaps and have to reapply. ◆ To form the fillet, pass the rounded edge of a stir stick held at an angle over the mixture to remove excess and form a smooth concave.

You may have to reshape the end of the stick to match the joint radius. Depending on the

temperature and the time elapsed, you can return the excess epoxy to the bag or discard it.

I usually discard it rather than risk having it kick off before I get a chance to shape the fillet.

Never add used epoxy to a new mix as the heat will dramatically decrease the working time. Carefully remove any excess on both sides of the fillet with a putty knife. ◆ If you applied enough epoxy, the fillet looks smooth in one pass. If there are gaps, apply more thickened epoxy and again smooth the joint. When fully cured, scrape or sand off any excess epoxy, then sand the wood (and fillets) with 120-grit paper. Apply two or more coats of unthickened resin-hardener mixture over the fillets, then paint or varnish to protect the epoxy from UV. © DIY boat owner 2001 1-888-658-2628

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P ROPER INSTALLATION OF THRU-HULLS IN CORED HULLS

BAD

Water

Water

BETTER

Filled core

Filled core

Inner skin

Filler

Sealant Filler

Backing block

(top) Bad: Even when well bedded, water will inevitably leak into the core; (middle) Better: Core removed adjacent to thru-hull and filled

DAVID AIKEN

Outer skin BEST

with thickened epoxy resin; (bottom) Best: Surrounding core completely removed and area filled with thickened resin mixture.

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PREVENTION S osmosis preventable? It's estimated that one in four fiberglass boats will get gelcoat blisters in its lifetime. The obvious answer is yes, there are preventative measures you can take to slow down and delay this occurrence.

The first line of defense is your boat's gelcoat.

Apply a barrier coating to new hulls before commissioning. Other protective measures such as dry storage, frequent spot repair of defects in the gelcoat and additional hull coatings will help slow down and delay the possibility of blisters forming.

Epoxy coatings applied on a sound, dry hull provide a durable, water-resistant

I

barrier; however no system is foolproof. Even epoxy coatings allow some absorption. The key to a successful repair is to remove all of the damaged laminate, thoroughly dry the hull and correctly apply the barrier coats. To reduce the possibility of blisters reoccurring keep the bilge as dry as possible and the boat well ventilated. Install additional vents to eliminate condensation. Solar-powered vents offer an efficient and affordable means of increasing air flow. Finally, check the barrier coat annually. —Jan Mundy

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