WE FIX LEAKY CHIMNEY SYSTEMS - Part II

WE FIX LEAKY CHIMNEY SYSTEMS - Part II

By Stuart Karanovich, Business Development Manager, SaverSystems

This is the second article in a three-part series dealing with remediation of water penetration problems in masonry chimneys for the professional chimney technician. In the first article, we dealt with types of water repellents and the brick and masonry structure of a chimney. In this article, we will deal with the special challenges that a chimney crown presents as it pertains to water penetration and remediation.

As stated in the preceding article, most experts agree that the durability of an external masonry chimney depends primarily on its ability to resist water penetration. A properly constructed and maintained crown plays a very important role in keeping water out of chimney systems. Unfortunately, most chimney crowns that we encounter were not built properly. It is usually not a question of “if” they will allow water penetration, but a question of when.

What Is a Properly Constructed Chimney Crown?

According to the Brick Industry Association, a proper crown should be constructed of pre-cast concrete, stone, or cast in place concrete, and should be two inches thick at its thinnest part. It should extend at least two-and a-half inches beyond the outside chimney walls in all directions and incorporate a drip edge at least one inch from the chimney on the underside of the crown to assist in shedding water. The crown should not contact the flue and should have an expansion gap of at least 3/8 of an inch around the perimeter of the flue to permit expansion as the flue heats up. There should be a bond break between the top course of bricks and the bottom of the crown. Additionally, the crown should slope downward from the flue liner to the outside edge of the crown at a rate of at least three inches per foot on all sides. Different localities have varying regulations regarding how high the flue liner must extend above the crown, with two inches being the minimum. In addition to the above guidelines, if we are going to cast in place a crown, it should be reinforced with at least ½ inch galvanized hardware cloth or welded wire fabric with a cross-sectional area exceeding 0.035 in, located mid-depth in the crown.

Why Chimney Crowns Leak

Simply stated, most chimney crowns leak due to improper materials and construction. Chimney crowns sit atop structures that extend above the roofline completely exposed to the elements. The crown sits at the apex of this structure aligned horizontally to the sun during the hottest portions of each day, subjected to UV radiation, rain, snow, ice and sleet.

Chimney crowns take more abuse from the elements than any other part of the chimney system. Given that they are rarely constructed properly, is it any wonder that they are often the culprit when water is entering the chimney?

Improper Crown Substrate

Often we are faced with a crown formed from a simple mortar wash applied to the top course of bricks and sloped upward, and attached directly to the flue. This is the most common and least effective crown we encounter. A mortar wash does not have the tensile strength of Portland cement or stone and will not function for long to protect the chimney from water intrusion.

Improper Flue Liner/Crown Juncture

If, when the crown was formed, a 3/8-inch gap around the crown/ flue liner junction was not maintained, the vertical movement as the crown heats and cools can cause the surface of the crown to crack. This cracking will occur not only around that juncture, but can spread across the surface of the crown, radiating from the flue liner to the outward edge of the crown. Additionally, if the expansion gap was formed but is inadequately filled with flexible high temperature caulk, water will enter the system at that juncture. Freeze-thaw cycles may then create cracks in the crown.

No Bond Break Between Chimney and Crown

If there is no bond break between the chimney and crown, then the crown is attached to the underlying brick and mortar that form the facing of the chimney, as well as whatever was used to support the weight of the crown when it was poured. Each individual material has a different temperature coefficient, meaning that for the same applied heat or cooling they will expand and contract at different rates.

When a crown is attached to all of these different materials, the result is a crown that can literally tear itself apart. As these different materials try to expand and contract, they meet resistance due to being coupled to each other, and cracking occurs, which in turn allows water to enter the chimney system through the crown.

A crown with a bond break so that it is not attached to the chimney, and is not attached to the flue tile, is called a floating crown.

Insufficient Slope of Crown

If the crown is not constructed in such a manner that allows water to run away from the flue tile to the edge of the crown, water may pool upon it. In areas with frequent freeze/thaw cycles, the repeated freezing of the pooling water can create cracks on the surface of the crown that will get incrementally larger with each ensuing freeze/thaw cycle.

Insufficient Overhang

If the crown does not extend sufficiently past the exposed facing of the chimney, then all water landing on the crown will sheet down the facings of the chimney. While this type of defect will not usually cause the crown itself to take on water, it will greatly increase the likelihood of water entering the chimney structure through the face of the chimney or the flashing.

Having a drip edge engineered into the bottom of the crown also helps prevent water from reaching the masonry face of the chimney.

What Do We Do? — Cast in Place Crown

When faced with a crown that has major defects or is severely deteriorated, the best choice is usually going to be demolishing the crown and cast in place a new crown using the above-mentioned BIA guidelines. A crown consisting of a sandy mortar wash with no overhang or drip edge, poured in direct contact with the flue tile, and major cracking and loose mortar is a great example and one I see regularly.

While this would be the ideal repair for this scenario, it is also probably going to be the most expensive, and sometimes the homeowner is unwilling to accept your proposal.

Repair Existing Crown

If the crown is structurally sound, then we have a variety of repair/ remediation options open to us. Using the above example, I would suggest cleaning the surface of the existing crown with a wire brush or powered wheel. Remove the debris created with a stiff nylon brush or blow it off with a can of compressed air. Then use a repair product made specifically for chimney crowns.

Generally, these products are in a class called elastomerics. Elastomeric is just a fancy way of saying that they are made of polymer formulas that when dry, maintain a degree of elasticity. This is important because when we employ this type of repair, we need to remember that we have not addressed the underlying cause of the problem, which is usually the different expansion and contraction rates of the existing crown and materials tied to it. What we have done is applied a waterproof membrane over the crown which will allow that movement to continue, without allowing water into the chimney system. The typical lifespan of this type of repair is in the range of ten to fifteen years depending on the polymer used in the repair. All the major chimney distributors carry these crown repair products.

What About Rain Caps?

In our above example, the existing crown did not provide for the two-and-a-half-inch overhang in all directions or have a drip edge to stop rainfall or snowmelt from sheeting down the face of the chimney. This can be remediated by selecting a chimney cover that extends beyond the face of the chimney. John Meredith, the founder of SaverSystems, recommends that this type of cover extend four inches past the face of the chimney in all directions. This will direct the majority of water away from the chimney, preventing water penetration problems in other areas of the chimney.

On a chimney with a crown that incorporates the two-and-a-half inch overhang and drip edge, a single flue cap may be a good choice.

On a chimney without a crown that incorporates adequate overhang, a bolt-on single flue cap may actually increase the amount of water directed down the face of the chimney. Precipitation that would have fallen into the flue may now be directed onto the inadequate crown.

Additional Considerations

If you are faced with the example above, it might be worth considering venting the chimney cavity. Chimney cavities that have large cross-sectional areas as compared to flue size can generate a lot of water inside the chimney cavity due to temperature and pressure differences between the flue and the air inside the cavity. (Think ice-cold glass of water on a cold day or mirror in the bathroom after a warm shower). Venting the cavity allows the pressure and temperatures to equalize and decreases the likelihood of condensation forming.

In addition, you might consider a concrete conditioner as a “primer” to be applied to the crown before the application of an elastomeric crown repair product, especially if the crown is constructed of a mortar wash or splay.

SaverSystems is testing one now.

Conclusion

Chimney crowns are subjected to extremely tough environmental conditions and are rarely constructed properly. As such, they require special attention to prevent unwanted water penetration. By learning to spot crown defects and choosing the right remediation action, you can prevent potentially expensive repairs for your customers and improve your bottom line. ■