How to Lay a Cement Foundation

Clear away all debris from the area you will lay your concrete slab. Use a spade or backhoe to dig down at least 6 inches where you wish to lay the concrete.

Prepare the ground that will support your concrete slab. This ground space is called the subgrade. Grade the surface so it slants slightly away from other foundation areas, or in a direction you want water to flow off.

Wet the smooth ground so that it is well soaked, but not muddy. Use a 2-by-4 as a tamper, or a commercial roller to compact the ground. This makes the earth hard and strong enough to support the weight of concrete.

Line the subgrade area with a gravel base at least four inches thick. The gravel gives the area better drainage so water can't damage the bottom surface of your slab. Lay a waterproof membrane over the gravel. This keeps ground moisture from developing and rising up under your slab.

Build a frame around the slab area with 2-by-4s. Use a hammer and pound nails in partially so they are easy to remove when the frame is no longer necessary.

Place two 2-by-4s on their sides long-ways across opposite sides of the slab and secure them so the top of the rail is level with where the top of the concrete slab should be when poured. Use your level to make sure the boards are perfectly level. These boards are called "screed rails" and a loose 2-by-4 is placed across them to run over the top of the concrete to make sure it is level. Only complete this step if you have an extra helper to complete the final smoothing step.

Lay rebar pipes every foot across the base of the slab for extra support with large surface areas, or for heavy equipment storage.

Pour cement into framework. Stand at one end of the straight-edge with another person on the opposite side and drag across the concrete surface using the screed rails as a guide to level the top.

Use hand trowels or commercial power trowel to finish smoothing the surface as it dries. If you are laying the slab by yourself and have not used screed rails and straight edge to get a level surface use a long-handled trowel as you pour wet concrete into the frame to get a starting surface as level as possible, then use hand trowels to finish. Remove all framework when slab is thoroughly dried.