How to Form Concrete Work

Prepare and excavate the site. Remove organic matter and topsoil from the planned pour site. Remove soil to a depth that allows for at least 4 inches of base material plus the thickness of the concrete slab, which varies depending on the purpose the slab serves. Install a proper base for the pour, which typically consists of at least 4 inches of compacted coarse gravel. For sites with clay soils or drainage problems, the gravel base should be a few inches thicker.

Select and cut the form boards. For small projects, three-quarter inch plywood may be suitable, while larger pours that require stronger forms call for 2-by-12-inch boards. Cut the boards to the correct length. If the form must be longer than the length of a single board, join boards together by nailing a 4-foot board over the joint on the exterior side of the form. Make two of form sides 3 inches longer than the length of the planned concrete to account for the overlap at the corner stakes.

Pound 2-by-4-inch wooden stakes into the ground where the planned corners will be. The stakes should be long enough to extend about 8 inches into the ground and a few inches above the top of the form boards that will be attached to them.

Nail one end of the board for the first side to a corner stake.

Attach the other end of the form side to the second corner stake using a level ensuring that the board is even.

Brace this first side of the form. Stretch a mason's line or string between the corner posts and attach a pair of 2-by-4 stakes to the form every 2 feet, one extending down and the other angled to act as a kicker keeping the other from bending out at the top. Use the string as a guide, making sure that the board remains aligned with the string and making adjustments as needed when pounding the braces in.

Place the board for the second side of the form. Use a carpenter's square for small forms. For larger slabs that require square corners, use the 3-4-5 method. For this method, measure and mark a distance that is a multiple of 3 feet on the placed side, then measure and mark a distance that is the same multiple of 4 feet on the side to be placed. Place the second form side at the angle so that these two points are the same multiple of 5 feet apart diagonally. Once the angle has been established and the board attached to a corner stake, use the same leveling and bracing techniques as with the first side.

Place the third, fourth and any other sides using the same techniques. If adding fill and reinforcement, wait and place the last side until all fill and reinforcement is added.

Add reinforcement for the planned pour. Larger slabs require rebar about one-half foot from the form along the slab’s perimeter and a grid with rebar spaced about every 4 feet. Smaller projects may only require metal lath or chicken wire for adequate reinforcement.

Lubricate the interior of the forms. Use a form lubricant sold for this purpose or motor oil.

Pour and level the concrete. Run a screed board across the top of the concrete to level the surface.

Finish the concrete as desired. Run a ball float over the concrete several times shortly after the pour. Once the concrete begins drying, add any final changes. In large slabs, adding grooves about every 10 feet allows for controlled shrinkage. Round off edges with an edging tool, set any anchor bolts as needed and smooth the surface with a float or add texture with a broom or another tool.