Preparing for Slab Foundation Construction
Foundation construction is an integral part of any building project. Although pouring a slab can be dirty back-breaking work, the process of preparing an area for a concrete slab is relatively easy. Here are a few of the things that will need to be done to prepare an area before any concrete is poured. It is important to note that the following article explains the things needed to prepare for an above ground house foundation slab. Below ground slabs and slabs needed for commercial buildings, may require different preparation techniques.
1 – Frame the Area for the Slab
Using 2-inch by 12-inch boards, make a frame around the area where the slab is going to be poured. This frame is referred to as the form. Premade forms can be used, but are often more expensive than using regular boards. Once the form is in place it must be reinforced with stakes and 2-inch and 4-inch boards so that when the concrete is poured its weight does not bow it.
2 – Level the Ground within the Form
Shovels and rakes must be used to completely level the ground within the form. Use a laser level to ensure the ground is totally flat.
3 – Dig Footings
All along the inside of the form, about 3-feet in from the perimeter, a trench that is 1-foot wide and around 7-feet deep must be dug. To ensure that the trench is dug in a straight line, it is common to run a string from one end of the form to the other. The trench is then dug directly below this string. It is important to dig the footing trench correctly because it is what keeps the slab from being able to tip back and forth as the soil gets wet, freezes, etc. Similar trenches must be dug in the areas that will sit beneath any load bearing walls of the house that is to be constructed on the slab.
4 – Tamp the Ground Down
To compact the soil as much as possible so that it is a stable base for the foundation, a tamper or jumping jack must be run across it. These tools slam a heavy weight against the soil over and over again forcing the particles in the dirt close together. On extraordinarily big jobs, a steam roller is sometimes used for this. Be sure to tamp the trenches dug for the footings, and remember: there is no such thing as too much tamping.
5 – Prepare Rebar
Push stakes down into the footing trenches so that their tops stick up to about the middle of the trench. Along these stakes rebar must be tied so that once the concrete is poured, the rebar will float in the middle of the trench and reinforce the footing. Once the rebar is placed correctly in the footing trenches, a rebar grid must be built above ground. Once again, use stakes to raise the rebar up off the ground. The rebar grid should cover the entire area within the form and each bar should be about 2-feet apart. This will create a series of 2-foot by 2-foot squares. Lash the rebar together with rebar ties and begin mixing the concrete that is to be poured.