How to Cast a Floor

Prepare the base of your floor first. Concrete performs best if cast on top of well-draining soil. Remove the sod and topsoil; if you have clay soils, remove the top 6 to 8 inches of soil to prepare a firm base. Pour 6 to 8 inches of gravel over the clay soil and tamp using a tamper. This creates a firm base.

Create a wooden form out of 2-foot-by-12-foot planks. Nail the planks together to create a square or rectangle the size of the floor you need to cast, using as many boards as you must to obtain the proper size. Place wooden stakes along the form every 2 feet to hold it in the soil. Once you've built your form, brace it every 2 feet by nailing 2-foot-by-4-foot boards to the stakes. Prop the boards at a 45-degree angle with the top end on the stake and the bottom end braced into the soil on the outside of the form.

Add 3 inches of gravel over your firm soil base, then tamp the gravel with a tamper. Leave a 12-inch trench around the entire area to create a concrete floor with thicker edges. If you created a gravel fill over clay soil, do not skip this step. Add more gravel instead, to form the base of your cast concrete floor. Leave 5 inches between the top of the gravel and the top of the form. Adjust the height of the form up or down if needed to get the 5 inches.

Spread plastic sheeting inside the form to cover the gravel base.

Drive rebar stakes into the ground 4 inches from the edge of the form, on the inside of the concrete form, with a sledgehammer. Lay one rebar stake every 12 inches to create an inner circle around the inside of the form. Once you have the rebar stakes in place, lay a horizontal layer of 1/2-inch rebar along the inside of the form, tying the rebar to the rebar stakes with tie wires. Lay a second 1/2-inch rebar above the first, creating reinforcement for your cast floor.

Create a grid rebar grid for the center of the floor by tying rebar together in a 4-foot grid. For example, for a 10-by-10-foot floor, lay three lengths of rebar 4 feet apart vertically. Crisscross three pieces of rebar horizontally to create a tic-tac-toe grid measuring 8 feet by 8 feet. Secure the grid with tie wires. Lay the grid in the center of the floor for now.

Have the driver delivering the wet concrete maneuver the truck so it is as close to your form as possible. Transport the mixed concrete from the truck to your form using a concrete chutes or by pouring the concrete into wheelbarrows and wheeling it over.

Pour concrete into the form, working quickly. As you pour, rake the concrete roughly into place with a concrete rake. This pushes the concrete, leveling it. Top off low spots to ensure an even floor.

Level the concrete using a concrete screed or a long piece of wood. Scrape the wood over the top of the form to level the concrete.

Grasp the rebar grid with a pry bar, pulling it up through the poured concrete until it sits in the vertical middle of the grid.

Work over the poured concrete with a bull float, to remove any gaps left by screeding. Pull the bull float across the concrete to use.

Work a metal edger around the inner lip of the concrete form to separate the concrete from the form so you can remove the form when the concrete dries.

Allow the concrete to dry enough so that you can walk on it without sinking. The time this takes depends on the weather; concrete dries faster in hot weather.

Cut grooves or joints into the concrete to prevent cracking. Cut grooves every 10 feet using a groover. Have a plywood board next to you to create a straight line, or your grooves may be crooked.

Let the concrete floor cure. To help it cure slowly, either spray the cast floor with curing compound or cover with plastic sheeting.

Remove the form after 24 hours to enjoy your new cast floor.