Construction Craft Worker Sample Chapter

6

INTRODUCTION TO FORMWORK UNIT 1

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FORMING MATERIALS AND METHODS

Spread footings for inverted T-shaped foundations are usually formed with 2 × 6 planks on residential projects and a minimum of 2 × 10 on commercial projects. See Figure 6-2. Planks are also used to form foundation walls in some forming systems.

Various methods are used for foundation form construction. All methods require sheathing, studs and/or walers, bracing, and a means of tying the form walls together.

See Figure 6-1.

With the exception of insulating concrete forms (ICFs), forms are temporary structures and should be constructed for easy dismantling. Duplex nails are used wherever practical since they can be quickly removed. Sheathing is fastened to stakes or studs with just enough nails to hold it in place. An adequate number of braces and ties should be used to keep the walls aligned and in place.

Framing and Bracing Materials A wall form is subjected to great pressure when concrete is placed. The pressure increases as the wall height increases. A fast concrete placement rate also places a greater strain on the forms.

Sheathing Various panel products may be used for form wall sheathing, including high-density overlay (HDO) plywood, Plyform®, and fibreglass-reinforced-plastic (FRP) plywood. Plyform is manufactured specifically for concrete form construction. Plyform panels are available in 1220 mm × 2440 mm (4′ × 8′) sheets and 16 mm (⁵⁄₈″), 19 mm (³⁄₄″), 26 mm (1¹⁄₈″), and 31 mm (1¹⁄₄″) thicknesses. HDO plywood, Plyform, and FRP plywood can be reused many times.

An area must be properly excavated before foundation forms are constructed.

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218 CONSTRUCTION CRAFT WORKER

Stud and Double Waler Foundation Wall Form

STUDS

PANEL SHEATHING

STEEL WEDGES HOLDING SNAP TIES PANEL SHEATHING

Walers, or wales, reinforce and stiffen foundation wall forms. Walers run horizontally and are toenailed to studs, which run vertically. For some applications, walers are fastened directly to the sheathing. The distance between walers depends on the thickness and height of the wall.

When 19 mm (³⁄₄″) panels are used to form low walls, studs or stakes are usually spaced 0.6 m (2′) apart.

Higher walls may require a spacing of 406 mm (16″) or 304 mm (12″).

Proper bracing is required to hold wall forms in position while concrete is being placed. One end of a brace is fastened to studs or walers and the other end is usually nailed to a stake driven into the ground.

Lumber used for walers, studs, and bracing is usually cut from 2 × 4s. Structural light framing lumber or another good grade of softwood lumber should be used.

Metal stakes may be used instead of wooden stakes to hold the forms in place. See Figure 6-3.

DOUBLE WALERS STUDS

CORNER TIES BOTTOM PLATE

FOUNDATION FOOTING

Figure 6-1. Concrete formwork consists of sheathing, studs and/or walers, and bracing. Note the use of corner ties to lace the walers together.

Figure 6-3. Reusable metal stakes may be used to hold planks in position. Duplex nails are driven through the holes provided in the stakes and into the planks.

The required plywood form thickness and size and spacing of framing depend on the maximum load.

Figure 6-2. Spread footings are commonly formed with 51 mm (2″) thick planks.

Chapter 6 — Introduction to Formwork

Ties Form walls must be tied together so they will not shift during concrete placement. Small form walls may be tied together by braces and wood cleats. See Figure 6-4.

Larger walls require metal ties to hold the form walls together and maintain the proper spacing between the walls.

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STEEL WEDGE

STAKE

2x PLANKS

Figure 6-4. Braces and wood cleats are sufficient to tie low foundation form walls together.

STEEL WEDGE

Figure 6-5 shows plank form walls tied together with steel wedge form ties. Figure 6-6 shows a system of snap ties and steel wedges used with single and double walers. Spreader cones maintain the correct spacing between the form walls. Buttons at the ends of the snap ties hold the steel wedges that are driven behind the walers. Breakbacks are grooves behind the spreader cones. After forms are stripped from foundation walls, the portion of the snap tie that protrudes from the wall is snapped off at the breakbacks.

Job-Built Forms The oldest method of form construction is the job-built method. Form walls may be sheathed with panels or planks. When 2x planks are used as sheathing, walers are not required and studs and stakes may be placed farther apart. See Figure 6-7.

STEEL WEDGE FORM TIE

Figure 6-5. Wedge ties are used to tie low form walls together.

Panel Forms Many craftworkers and contractors consider panel forms a more efficient method of form construction than builtin-place forms. Panel forms consist of studs and top and bottom plates nailed to a 1.2 m × 2.4 m (4′ × 8′) panel.

See Figure 6-8. When the sections are set in place, the end studs are fastened to each other with duplex nails.

Snap ties are laid out horizontally at 0.6 m (2′-0″) OC unless designated differently by an engineer. Vertical tie spacing depends on wall height and concrete placement rate. The first tie of the horizontal layout must clear the adjoining wall when doubled and then continue 0.6 m (2′-0″) OC.

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Forms Using Snap Ties and Snap Brackets PANEL SHEATHING SINGLE WALER

SINGLE WALER

SNAP BRACKET

SNAP BRACKET

STEEL SNAP TIE

BUTTON SPREADER CONE

BREAKBACK

SNAP TIES WITH SINGLE WALERS HOLDING SHEATHING STUD

STUD DOUBLE WALER

DOUBLE WALER

STEEL SNAP TIE

STEEL WEDGE SPREADER CONE

PANEL SHEATHING

BREAKBACK

SNAP TIES WITH DOUBLE WALERS AND VERTICAL STUDS HOLDING SHEATHING Figure 6-6. Snap ties and steel wedges are commonly used to hold form walls together. Spreader cones set the walls to the correct width. The buttons at the ends of the ties hold steel wedges that are driven behind the walers. Snap ties are designed for both single-waler and double-waler systems. Breakbacks are grooves behind the spreader cones. After the forms are stripped from the foundation wall, sections of snap ties protruding from the wall are snapped off at the breakback points when bent back and forth.

Chapter 6 — Introduction to Formwork

221

Job-Built Foundation Wall Forms

BRACE ANCHOR STAKE

5

TEMPORARY BRACE DIAGONAL STUDS BRACE

SNAP TIES INSERTED

3

PANEL SHEATHING NAILED TO STUDS

4

SNAP TIE HOLES DRILLED

6

WALERS PLACED

HORIZONTAL FORM BRACE

STUDS

DOUBLE WALERS

1

KEYWAY DRAIN TILE

GRAVEL

2

BOTTOM PLATE NAILED TO FOOTING

STUDS TOENAILED TO BOTTOM PLATE

FOOTING

BUILDING LINE (INSIDE FACE OF PANEL SHEATHING)

VERTICAL REBAR

1

Fasten bottom plate to concrete footing.

4

Drill snap tie holes.

2

Toenail studs to bottom plate. Tie studs together with temporary brace.

5

Insert snap ties through holes and between walers.

3

Apply sheathing to inner face of studs.

6

Place walers.

Figure 6-7. Foundation wall forms are constructed over footings. A bottom plate is fastened to the concrete. Studs are set up, temporarily tied together, and braced. Sheathing is then applied to the inner face of the studs. The walers are then placed.

Panel forms can be constructed in the shop or on the job. Panel forms are convenient for use in housing developments where one foundation design is repeated. The panel form sections can be reused after being stripped from the foundation walls. Tie holes are patched with small pieces of sheet metal. Patented wood and metal panel forms can be rented or purchased.

Concrete pressure on the forms is affected by several factors, including concrete temperature, placement rate, concrete slump (consistency), type of cement, concrete density, method of vibration, and height of the forms.

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FILLER PANEL FORM SECTION PANEL (OUTSIDE WALL)

HORIZONTAL FORM BRACE

BRACE ANCHOR STAKE

FIRST TIES MUST CLEAR ADJOINING WALL WHEN DOUBLED PANEL FORM SECTION (OUTSIDE WALL)

BRACE 0.3 m (1′-0″) 0.6 m (2′-0″)

ANCHOR STAKE

PANEL FORM SECTION

0.6 m (2′-0″)

FOOTING HORIZONTAL BRACE GRAVEL BUILDING LINE

DRAIN TILE

KEYWAY

VERTICAL REBAR EXTENDING FROM FOOTING

Figure 6-8. Panel sections are constructed in the shop or built on a job site. The sections can be reused many times.

Footings for slab-at-grade foundations may be formed by excavating a trench. Rigid insulation is placed along the outer edge of the footing and beneath the outer edge of the slab. Plastic tubing is installed in this slab to provide radiant heat for the structure.

Figure 6-9 shows lightweight aluminum forms.

Round stakes driven through holes in the aluminum sections hold them in place. Wedge locks at the stakes allow each section to be positioned at the proper height.

Figure 6-10 shows a lightweight aluminum panel system for foundation walls.

Western Forms, Inc.

Figure 6-9. Reusable aluminum forms are secured in position using round stakes driven through holes along the edges. Wedge locks at the stakes allow the height of each form section to be adjusted.

Chapter 6 — Introduction to Formwork

223

GROUND-SUPPORTED SLABS

Figure 6-10. Lightweight aluminum form panels were used to form this basement foundation wall. Some of the panels are still in place on the wall at right.

FLATWORK Flatwork is the construction of indoor and outdoor concrete slabs, patios, walkways, and other flat, concrete, horizontal surfaces. Flatwork preparation includes accurate layout of the finished slab elevation with a builder’s level, transit level, or laser level. When the elevations are established, a screed system and/or edge forms are constructed. Edge forms are used in flatwork such as driveways or walkways to retain the concrete in a specific area. A screed system is used to maintain proper floor elevations in the interior areas of the flatwork.

Preparations must also be made for construction joints, isolation joints, and expansion joints. Construction joints are used where fresh concrete butts against the edge of a section of concrete that is set. Isolation joints are used to prevent cracking between two adjacent sections of concrete. An isolation joint is usually filled with caulking compound or asphalt-impregnated material.

Expansion joints are used in large sections of flatwork where expansion and contraction forces are anticipated.

Driveways and walkways are constructed for vehicle and pedestrian use. Driveways are 102 mm to 152 mm (4″ to 6″) thick and are reinforced with welded wire reinforcement or rebar. Public sidewalks, front walks, and service walks are commonly located around residential structures. Walkways are usually 102 mm (4″) thick, although thicker slabs reinforced with rebar may be required where heavy vehicles pass over.

Ground-supported slabs are commonly placed for ground-level floors of residential and commercial buildings that do not have basements. For these types of structures, ground-supported slabs are usually less costly to build than wood-framed floors. Ground-supported slabs are also used in the construction of garage floors and below-grade basement floors.

The design and construction of ground-supported slabs are based on soil properties at the job site. In addition, moisture and thermal conditions and the shape and slope of the lot are considered in the design of ground-supported slabs.

Properly drained, dense soil mixtures such as gravel, sand, and silt generally provide a good base for groundsupported slabs. The suitability of soil conditions on a job site is often determined by past practice in the area.

However, if there is any question about the soil composition at a particular job site, a qualified soil engineer should conduct a soil investigation.

Moisture conditions are also considered in the construction of ground-supported slabs. The amount of predictable surface water from precipitation (rain and snow) and the amount of groundwater can result in a volume change and/or reduction of the bearing capacity of the soil. Problems may also result from the combination of moisture and temperature conditions. Low temperatures cause groundwater to freeze and pose the danger of frost heave below the slab.

Ground-supported slabs are placed on level ground.

Steeply sloped lots are not practical for groundsupported slabs because of high excavation costs and potential water drainage problems.

Slab-on-Grade Floors Slab-on-grade (also called slab-on-ground) floors are usually integrated with a slab-on-grade foundation system. Slab-on-grade floors are placed after the foundation has been constructed, or are placed monolithically with the foundation walls. The floor slab is at the same elevation as the top of the foundation wall. In most slab-on-grade floors, the top surface of the slab is at least 203 mm (8″) above the finish grade level at the perimeter of the foundation walls. Floor slabs for residential buildings are a minimum of 102 mm (4″) thick. Thicker floor slabs may be required in commercial structures that support heavy loads.

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When a slab-on-grade floor is placed after the foundation has been constructed, rigid insulation is recommended around the perimeter of the slab to reduce heat loss. The insulation should be at least 25 mm (1″) thick and extend 609 mm (24″) vertically below grade level or 609 mm (24″) horizontally under the concrete slab.

See Figure 6-11.

3.

4.

5.

Slab-on-Grade Insulation RIGID INSULATION

RIGID INSULATION

FLOOR SLAB

FLOOR SLAB

mm 203 mm ((8″) 8″) MIN MIN

609 mm (24″)

102 mm (4″) MIN

102 mm 609 mm (4″) (24″) MIN

7.

FOOTING

HORIZONTAL INSULATION PLACEMENT

6.

VERTICAL INSULATION PLACEMENT

Figure 6-11. Rigid insulation extends 609 mm (24″) horizontally or vertically from the perimeter of a slab-on-grade foundation. The top surface of the slab is a minimum of 203 mm (8″) above the outside grade level.

Site Preparation. Site preparation, including all groundwork, must be completed before the concrete is placed for a slab-on-grade floor. Site preparation may only require removing the topsoil to reach undisturbed soil, or it may require excavating deep enough to place a layer of compacted fill and a gravel base course. See Figure 6-12.

Groundwork provides support for the slab and controls ground moisture. Vapour barriers are used to contain ground moisture beneath the slab. All pipes and ducts to be embedded in the concrete must be set in place before the concrete slab is placed. Site preparation for a slab-on-grade floor requiring fill and a gravel base course is as follows: 1. Remove all topsoil and excavate to firm, undisturbed soil. Excavation must be deep enough to hold the layers of fill and gravel.

2. Place and compact fill material. Fill is required when the ground surface is uneven or where a

8.

gradual slope must be levelled. The fill should be compacted in 102 mm to 304 mm (4″ to 12″) courses by using hand or power equipment. Fill material should be free of vegetation and other foreign material that might cause uneven settlement.

Install pipes, drains, ducts, and other utility lines.

Erect formwork.

Place a gravel base course at least 102 mm (4″) thick to control the capillary rise of water through the slab bed. The base course also provides uniform structural support for the concrete slab and reduces the amount of heat lost to the ground.

Place a moisture-resistant vapour barrier over the base course, directly beneath the floor slab, to prevent moisture from seeping through the slab. Six-mil polyethylene film is commonly used as a vapour barrier. All joints are lapped at least 152 mm (6″) and should fit snugly around all projecting pipes and other utility openings. Precautions must be taken so that the vapour barrier is not punctured during construction work.

Place perimeter insulation along the foundation walls if required.

Place reinforcement in the slab according to the foundation section views. The reinforcement is usually at the centre of the slab or approximately 25 mm to 38 mm (1″ to 1¹⁄₂″) from the top surface.

Site Preparation REINFORCEMENT

CONCRETE SLAB

VAPOUR BARRIER GRAVEL BASE COURSE UNDISTURBED SOIL

COMPACTED FILL

Figure 6-12. The building site for a slab-on-grade floor must be excavated to undisturbed soil. Compacted fill, a gravel base course, and a vapour barrier are placed in the excavation.

Chapter 6 — Introduction to Formwork

Forming Slab-on-Grade Floors. When placing a floor slab independently of the foundation walls, forming the edges of the slab is not required because the perimeter of the slab butts up against the foundation walls. When the concrete slab is placed monolithically with the foundation walls, the outside foundation form boards also form the edges of the slab. This forming method often consists of 51 mm (2″) thick planks held in place with stakes and braces.

Construction Joints. A construction joint is a joint used where two successive placements of concrete meet, across which a bond is maintained between the placements. A construction joint is formed where a fresh concrete section butts up against the edge of a concrete section that has already set. A construction joint is formed by staking down a 51 mm (2″) thick bulkhead at the outer edges of the concrete placement area. The top of the bulkhead is positioned at the height of the floor surface and a bevelled key strip is fastened to the bulkhead. Metal, wood, and premoulded key strips are commonly used to form a keyway for the floor. The keyway secures the edge of the next section in position.

Keyed joints are not recommended for industrial floors.

Metal dowels should be used in slabs that carry heavy loads. See Figure 6-13.

Concrete for large floor areas in commercial buildings such as warehouses, factories, and stores is placed in sections. Therefore, provision must be made for construction joints when placing large floor slabs. See Figure 6-14.

Screeding. Placing concrete for large floor sections requires the use of a screed system to maintain proper floor elevations in the interior areas of the slab. The screed is positioned with its bottom edge at the finish elevation of the floor surface. Wood stakes or screed supports hold the screed off the ground and allow rebar to be positioned. Lines are stretched from the top of the outside walls or form boards to adjust the screeds to their proper height. A strike board acting as a straightedge to level the concrete is placed between the screed boards. A strike board is a wood or metal straightedge used for screeding concrete. Strike boards are held at the same level as the screeds by cleats nailed at opposite ends. See Figure 6-15. As the concrete is being placed and consolidated, cement masons strike off the concrete by moving the strike board along the screeds with a saw-like motion. The screeds and their supports are then removed from the concrete.

225

Bulkheads 51 mm (2″) BULKHEAD

METAL KEY STRIP

WOOD KEY STRIP

EDGE BEFORE REMOVING BULKHEAD

PREMOULDED KEY STRIP

EDGE OR SAW TO MATCH CONTROL JOINT 1:3 SLOPE

127 mm (5″)

25 mm (1″)

KEYWAY

13 mm (¹⁄₂″) MINIMUM

KEYED CONTROL JOINT POUR #2

POUR #1

STEEL DOWEL

REBAR

STEEL DOWEL CONTROL JOINT Figure 6-13. Bulkheads are used to form construction joints when a concrete slab is placed in sections. Premoulded key strips or metal dowels are permanently embedded in the slab.

Large Floor Slabs

The Euclid Chemical Company

Figure 6-14. Concrete is placed in sections for large industrial or commercial concrete slabs.

226 CONSTRUCTION CRAFT WORKER

Screeds can also be placed with the top edge flush with the finish surface of the concrete. Two screeding methods may be used with this system. In one method, a section of the floor slab is placed and struck off to the screeds. The screeds are then removed and the concrete is placed for the next floor section. In the second method, the screeds remain in place until the entire slab has been placed. The screeds and their supports are removed and the cavities are filled with concrete. Metal pipe screeds supported by wooden stakes or adjustable chairs are often used with this method. See Figure 6-16. Mechanical equipment is also available for screeding operations and is often used when placing larger slabs.

On large concrete slabs, placement, screeding, and troweling operations often occur at the same time.

Screed Systems STRIKE BOARD

CLEAT NAILED TO STRIKE BOARD

STRIKE BOARD

CLEAT NAILED TO STRIKE BOARD SCREED

ADJUSTABLE METAL SUPPORT

SCREED STAKE

WOOD STAKE SCREED SUPPORT

ADJUSTABLE METAL SCREED SUPPORT

SCREED

PLYWOOD CLEATS NAILED TO STRIKE BOARD

STRIKE BOARD

STRIKE BOARD

FORM BOARD

BOTTOM OF SCREED SET TO LINE THAT IS FLUSH WITH TOP SURFACE OF FLOOR

STAKE SUPPORTING SCREED

STRIKE BOARD RESTS ON TOP OF FORM BOARD

TOP OF FORM BOARD FLUSH WITH TOP OF FLOOR SLAB

STAKE

BRACE CONCRETE ON THIS SIDE OF SCREED WOULD SLOPE FROM LEFT TO RIGHT SINCE SCREED IS ON TOP OF FORM BOARD

Figure 6-15. A screed system is used to strike off concrete placed for a concrete floor slab. The screed is supported by wood stakes or adjustable metal supports.

Chapter 6 — Introduction to Formwork

LOW C A RBON FA C T When setting steel reinforcement for a slab, reinforcement must be set to the proper depth. Setting steel reinforcement as little as 13 mm (½″) above its design position in a 152 mm (6″) slab can reduce the live loadbearing capacity of the concrete by as much as 20%.

227

to the area beneath the control joints. Control joints may be formed with a special grooving tool when the concrete is being finished. They may also be cut into the slab after the concrete has set using a power saw equipped with an abrasive blade. Recommended spacing for control joints is 4.6 m to 6 m (15′ to 20′). See Figure 6-17.

Control Joints 13 mm (¹⁄₂″) MAXIMUM RADIUS

Pipe Screeds

ONE-FOURTH OF SLAB THICKNESS

STRIKE BOARD

PIPE SCREED

FLOOR GRADE LINE

TOP OF PIPE FLUSH WITH FLOOR GRADE GRAVEL BASE COURSE NAILS SECURE PIPE

WOOD STAKE SUPPORT

HAND-TOOLED CONTROL JOINT ONE-FOURTH OF SLAB THICKNESS

6 mm (¹⁄₄″) MINIMUM

ADJUSTABLE METAL SUPPORT

Figure 6-16. Metal pipe screeds are used to support a strike board.

Control Joints. Control joints (also called relief or contraction joints) confine and control cracking in concrete slabs caused by expansion and contraction. A control joint is a groove made in a horizontal or vertical concrete surface to create a weakened plane and control the location of cracking. A control joint is one-fourth the slab thickness. Cracks occurring in the future will be confined

SAWED CONTROL JOINT Figure 6-17. Control joints in a concrete slab confine cracking resulting from expansion and contraction of the slab.

Control joints are hand tooled or cut into the slab.

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Expansion Joints. An expansion joint (isolation joint) is a joint that separates adjoining sections of concrete to allow for movement caused by expansion and contraction of the slabs. Expansion joints are used in slabs that cover large areas of commercial buildings, and where a great amount of expansion and contraction is anticipated. Expansion joints run through the complete thickness of the slab. One common method is to place a piece of preformed asphalt-impregnated material in the joint. The fiber material is tacked to the form board before the concrete is placed and remains in place when the form board is removed. See Figure 6-18.

Expansion Joints FORMED FIBRE MATERIAL

STAKE

NAILS

FORM BOARD

FORMED ASPHALT-IMPREGNATED FIBRE MATERIAL TACKED TO FORM BOARD

LOW C A RBON FA C T FIRST SLAB PLACED

Expansion joint material must be compressible and may be manufactured from asphalt impregnated fiberboard, HDPE foam, rubber, cork, or closed-cell neoprene.

An expansion joint is also used to prevent cracking between a slab and foundation walls. Without an expansion joint, there is a weak bond between the floor slab and foundation wall since the slab is not placed monolithically (at the same time) with the wall. Ground heaving may also cause cracks in and around the slab, allowing ground moisture to seep into the basement.

Expansion joints usually consist of caulking or asphaltimpregnated material placed around the perimeter of the slab to separate the floor slab from the foundation walls.

When using caulking for an expansion joint, an oiled, wedge-shaped strip is placed against the foundation wall before the slab is placed. The strip should be 13 mm (¹⁄₂″) thick with the width equal to the thickness of the floor slab. After the slab has been placed and the concrete has set, the oiled strip is removed. The area between the slab and the wall is then filled with a caulking material.

When using an asphalt-impregnated strip, a 13 mm (¹⁄₂″) thick premoulded strip is placed against the foundation wall. After the slab is placed, the asphalt-impregnated strip remains in the concrete. See Figure 6-19.

LOW C A RBON FA C T Expansion joints are used to absorb stresses from the expansion and contraction caused by changes in temperature.

NAILS AND FIBRE MATERIAL REMAIN IN CONCRETE AFTER FORM BOARD IS REMOVED FIRST SLAB

SECOND SLAB SECTION IS PLACED

COMPLETED EXPANSION JOINT Figure 6-18. An expansion joint is used when a great amount of expansion and contraction is anticipated.

Concrete Reinforcement A wall made of concrete has a great deal of compressive strength, which is its ability to hold up under vertical pressure. Vertical pressure is exerted on a foundation by live and dead loads, including the weight of the structure, furniture, and appliances. However, concrete has far less resistance to lateral forces, which push against the wall sides. Lateral pressure is exerted on a foundation by the soil.

Chapter 6 — Introduction to Formwork

229

Expansion Joint Material FOUNDATION WALL 13 mm (¹⁄₂″) EXPANSION JOINT CONSISTING OF CAULKING OR PREFORMED ASPHALT-IMPREGNATED MATERIAL FLOOR SLAB

VAPOUR BARRIER FOOTING

REBAR

Figure 6-20. A keyway helps to secure the bottom of a foundation wall to the footing. Note the drain tile placed around the outside of the footing.

GRAVEL BASE COURSE

Figure 6-19. An expansion joint contains caulking or a preformed asphalt-impregnated strip.

Reinforcement such as rebar, welded wire reinforcement, or plastic or steel fibers is used to improve resistance of concrete to lateral pressure. Unreinforced concrete has little tensile strength, allowing it to crack easily when bending stress is applied.

Welded Wire Reinforcement Welded wire reinforcement (WWR), or wire mesh, is heavy-gauge wire joined in a grid and used to reinforce and increase the tensile strength of concrete. WWR helps prevent cracks in the concrete from occurring later due to settlement. Welded wire reinforcement is available in a variety of sizes with either smooth or deformed wire.

Wire size is denoted by numbers and letters. The first two numbers specify wire spacing; the second two numbers specify wire size. A letter in front of the wire size number specifies whether a smooth (W) or deformed (D) wire is used. For example, 9 gauge wire has a diameter of 0.1483 (3 mm or ¹⁄₈″).

WALLS Form walls are erected after the footings have hardened and set. See Figure 6-20. Bottom plates are fastened to the fresh (green) concrete as a base for the outside form walls of either job-built or panel forming systems.

Except in the case of low form walls, rebar is usually installed after the outside form walls are set in place.

See Figure 6-21. When the rebar has been installed, the inside form walls are constructed. When a large amount of reinforcing steel is required, the steel is typically placed by reinforcing-metal workers.

Figure 6-21. Outside form panel sections are fastened to the top of the footing. Note the snap ties projecting from the panels and the rebar at the back wall.

Rebar should be clean and free of loose rust and other debris, form oil, and form-release oil when installed in forms. Rebar must be positioned and secured in place so it will be covered by an adequate layer of concrete.

Rebar is typically fastened to adjacent rebar using wire ties. See Figure 6-22.

230 CONSTRUCTION CRAFT WORKER

CLAMPS AND SNAP TIES

BRACE NAILED TO STUD

DOUBLE WALER

Figure 6-22. Rebar projecting from the footing will be tied to reinforcing steel in the foundation wall. The rebar is temporarily capped to ensure worker safety.

Preparations must be made for door and window openings when the form walls are built. Finish window frames and door jambs may be attached to the form walls. Door or window bucks are attached to the form walls if finish frames and jambs are not installed.

A traditional double-waler outside wall is shown in Figure 6-23.

Patented panel systems are widely used in the construction of foundation walls. Patented panel systems generally consist of panel sheathing set in metal frames. See Figure 6-24. Depending on the manufacturer, the panel sections are secured to each other with wedge bolts or clamps. When wedge bolts are used to secure the panel sections together, one wedge bolt is inserted in a slot provided in the side rails and the other wedge bolt is inserted in a slot in the first wedge bolt.

See Figure 6-25.

PANEL SHEATHING ADJUSTABLE FORM ALIGNER BRACE

STEEL STAKE

Figure 6-23. A double-waler wall system is commonly used to form high foundation walls.

Figure 6-24. Patented panel systems consist of panel sheathing set in metal frames.

Chapter 6 — Introduction to Formwork

231

After form walls have been set for one side of the wall form, wire ties or snap ties are inserted into holes in the panels. Some patented forms have dadoed slots in the side rails for wire ties. See Figure 6-27. Wire ties or snap ties properly space and hold together opposite form walls.

For many patented panel systems, walers are required only at the upper section of the form walls. The lower ends of the form walls are secured to the footing. Figure 6-28 shows a double-waler snap tie-and-clamp system.

Figure 6-25. Wedge bolts secure panel sections together.

One wedge bolt is inserted in a slot in the side rails and another wedge bolt is inserted in a slot in the ďŹ rst wedge bolt.

Many patented panel systems are aligned and secured with wood braces, which are equipped with metal turnbuckles on their upper ends. The turnbuckle is secured to the panel with wedge bolts or duplex nails. See Figure 6-26. The lower end of each brace is nailed to a wood or metal stake driven into the ground. Panels are then adjusted to the proper position by turning the turnbuckle.

High-density overlay (HDO) plywood panels have resin-treated ďŹ bre overlays bonded to plywood with waterproof glue under heat and pressure. HDO plywood concrete forms can be reused 20 to 50 times if properly maintained.

Figure 6-27. Wire ties space and hold together opposite wall forms.

Figure 6-26. This patented panel system uses wood braces with metal turnbuckles that are secured to walers with duplex nails.

Figure 6-28. Walers are placed toward the top of a patented panel wall form with a snap tie-and-clamp system.

232 CONSTRUCTION CRAFT WORKER

Layout of Building Corners Using the 3-4-5 Method 30.5 m (100′-0″)

FRONT PROPERTY LINE

FRONT PROPERTY LINE

LOT CORNER STAKE Z N SIDE PROPERTY LINE 22.7 m (75′-0″)

LOT CORNER STAKE X SIDE STAKE A PROPERTY LINE

LOT CORNER STAKE X

4.6 m (15′-0″) FRONT SETBACK

6m (20′-0″)

LOT CORNER STAKE Y

2 Measure the front setback (6 m [20′-0″]) from the front property line and

1 Stretch lines from lot corners X,Y, and Z.

the distance from the side property line to the building (4.6 m [15′-0″]) at the same time. Drive stake A and place a nail establishing first building corner.

LOT CORNER STAKE X LOT CORNER STAKE X STAKE B

STAKE A

1.8 m (6′-0″)

4.6 m (15′-0″)

STAKE A STAKE C

SIDE PROPERTY LINE

10.6 m (35′-0″) LOT CORNER STAKE Y

WIDTH OF BUILDING

STAKE B

3 Measure the distance from the side property line to the building (4.6 m

[15′-0″]). Measure the width of the building (10.6 m [35′-0″]) from stake A. Drive stake B and place a nail establishing second building corner.

4 Stretch a line between stakes A and B.

Drive stake C 1.8 m (6′-0″) from stake A and align with stakes A and B. Drive a nail exactly 1.8 m (6′-0″) from the nail on stake A.

STAKE E STAKE D

2.4 m (8′-0″) STAKE A

STAKE F

10.6 m (35′-0″)

STAKE D

3 m (10′-0″) 18.3 m (60′-0″) STAKE A STAKE C STAKE B

5 Measure 2.4 m (8′-0″) from stake A and 3 m

(10′-0″) from stake C. Drive stake D and place a nail exactly where the measurements intersect. Angle DAC is a 90° angle.

The 3-4-5 method can be used to lay out building corners.

STAKE B

6 Stretch line from stake A and over stake D. Measure length of building

18.3 m (60′-0″) from stake A. Drive stake E and place a nail establishing third building corner. Measure length of building from stake B 18.3 m (60′-0″). Measure width of building from stake E and place a nail establishing fourth building corner.