The Construction Phases of a Concrete Slab Foundation

Written by g.d. palmer
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The Construction Phases of a Concrete Slab Foundation
Framing can begin once the slab has hardened. (Construction and slab image by jcpjr from

Concrete slab foundations are extremely common in newer construction, especially in areas where the local soil doesn't allow for a basement. Building a concrete slab foundation is relatively straightforward, but does require some attention to detail. Following the right steps to build your concrete foundation will help it last a lot longer, whether you're building a house of your own, an addition or just a shed.


Step 1 in building a slab foundation is to determine the type. According to the Concrete Network, slabs come in 3 major varieties, depending on the building location and conditions. Traditional slab foundations are flat and supported on a T-shaped structure at the corners. This method works well in areas where the ground freezes. Slab-on-grade foundations have a thicker edge, which forms a footing, and work better where no freeze is likely. Frost-protected slabs are best on heated structures, and include insulation that keeps the footing from freezing. These are a good choice in areas subject to heavy freezes.


Once you know what kind of slab you're going to build, you'll need to mark out the exact shape of the building and set up batter boards. Then, excavate the area within the marked space. Take care not to build too deep. According to Repair Home, you can't build a foundation on soil that has already been disturbed. That means no backfilling if you overdig.


Slab foundations require structural support in the form of rebar or other steel. These materials should be placed before pouring any concrete. The rebar helps the foundation resist soil movement caused by freeze-and-thaw conditions.


Once the rebar is in place and the footing is the right shape, workers can fill it with concrete to the level of the ground. This concrete must be allowed to harden for several days before any other work can continue. Once the concrete has hardened, workers can place any foundation walls, plumbing or other material to be embedded into the slab itself.


Before you pour the slab, prepare the area by filling it with a layer of gravel and covering that gravel with 6 mil plastic vapour barrier. This keeps moisture from wicking up into the foundation. Then pour the concrete and smooth it to be flush with the foundation walls. Wait several days to let the slab harden completely, then move on to framing.

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