How to Lay a Slab Foundation for a Remodel

Photo credit to divemasterking2000.

If you are currently working on a home remodeling project, you might find that you need to lay a new concrete slab foundation as part of the project. As a general rule, this type of slab foundation is better left to the professionals, as it requires a good amount of expertise, work and attention to detail. It’s not like choosing wall decorations or centering a fish metal art on a focal wall!

The technical term for a concrete slab that will be supported by the ground is a "slab-at-grade." This is somewhat different than just laying a regular slab of concrete. As opposed to regular slabs of concrete that are traditionally poured over existing supports, a slab-at-grade is supported entirely by the ground underneath. As such, special techniques need to be used in order to create a solid foundation.

Proper Ground Preparation is Key

It is important to understand that the ground must be prepared properly, since it will be solely responsible for supporting the concrete slab. This involves getting it flattened and leveled perfectly, in addition to removing any kind of debris. The ground under the slab will also need to be very compacted, which is generally accomplished by moistening the ground and compressing it evenly. It should be designed in a fashion that water will flow away from the foundation so that puddles cannot form.

Applying Gravel and a Waterproof Membrane

Once the ground is properly prepared, the next step involves putting down a layer of gravel so that water can move easily underneath the slab after it is installed. Between the gravel and the slab you will also need to put down a waterproof vapor barrier so that the slab won't absorb ground moisture. Without these two preparation steps, any concrete slab that you lay would be in danger of future damage and instability.

Creating a Frame for the Poured Concrete

Because the concrete is being poured directly on top of the ground, you will need some type of frame that will form the shape of the concrete slab. This is accomplished by using 2x4 rails to contain the poured concrete. These wooden rails are also used after the concrete is poured for leveling purposes, as another 2x4 can be pulled along the wooden rail supports to level off the top of the concrete slab evenly. This frame must be securely attached to the ground by using stakes before the concrete is poured.

Pouring the Concrete

Once the frame has been constructed, it is time to mix the concrete. Always choose a grade of concrete that is designed for slab construction, and mix it carefully according to the manufacturer's directions. The mixed concrete can then be poured into the frame, using a 2x4 slid along the top of the wooden frame to level it. This leveling process also removes any excess concrete to form a smooth surface. Once the leveling is complete, the frame can be removed and any final finishing details or necessary smoothing can be done using a trowel as the slab continues to dry. After the construction of the concrete slab is complete, all that remains is to let the concrete cure and dry completely.