DIY Guide to Laying Slabs

Updated February 21, 2017

If you are planning a home addition, the first step is to get a foundation under the proposed building. The best way for this to happen is to lay a concrete slab. Luckily laying a slab is a pretty easy project to undertake without the need to bring in a contractor.


The first step to this process is the actual location of the slab. The ground needs to be relatively level (if you are going to build on a hill, you should not try to excavate the dirt yourself). Also make sure that there are no obstructions above the ground (trees and bushes) or below ground (pipes and electrical wires)


Once you have the location set, you should be ready to build the slab. A concrete slab is built inside a frame made out of wooden boards. The size of these wooden boards determines the thickness of the concrete slab. One thing to remember is that a slab that's thicker will be sturdier. Therefore, if you are pouring a slab which will be used as a patio, using 2-by-4s will be appropriate as there will not be a lot of weight on it. If you are placing something heavier on the slab, you will need to move to a thicker wood (2-by-6, 2-by-8 or even 2-by-12).

Building the frame

After the wood has been purchased for the appropriate thickness, measure the area where you will be placing the slab and cut the wood according to the size of the slab. Once the wood has been cut, place it together to form your rectangular frame. Make sure this frame is square by using a carpenter's square on the corners and measuring the diagonals. If the diagonals are the same length, the entire frame is square. Place the frame in the area where the slab will be and pound wooden stakes into the ground next to the frame. Nail the wooden stakes into the frame to attach it directly to the ground. The last step in the frame preparation is digging a trench around the perimeter to give the slab more support. The trench should be four inches deep and eight inches wide.

Pouring the slab

Mix dry concrete with water to form the concrete mix. The concrete should be the consistency of wet mud. To determine how much concrete you will need, multiply the length by the width by the depth to get the volume of the frame which will give you the minimum amount of concrete you will need for the job. Before you run out and buy that amount of concrete, you will need to add the volume of your trench to the volume of the frame to get the true amount you need. Once the concrete is mixed, fill the frame until it is between three and six inches from the top. Lay pieces of rebar along the perimeter of the frame to add more support and fill the frame the rest of the way. Smooth out the top of the concrete with a trowel and let the concrete dry. Once the concrete is dry, you can remove the frame.

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About the Author

R.L. Cultrona is a San Diego native and a graduate of San Diego State University. She holds a Bachelor of Arts in theater, television and film with a minor in communications and political science. She began writing online instructional articles in June 2009.