How to Build a Concrete Foundation

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  • 192-336 hours
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What You'll Need
Cement mixer
Spirit level
Measuring tape

If you're building a new extension to your house, then you need to know how to form a concrete foundation floor. Concrete foundations can be poured into any part of your house; however, it's important to make sure that the pouring is done properly so that the floor will last for many years to come.

The stability of the concrete foundation affects the structure and integrity of the whole building. If there are any weaknesses in the foundations, they will detriment the building. Laying and forming concrete foundations is actually very easy with the right tools.

Step 1 - Work Out the Size

Calculate how deep you need to dig the whole for the concrete slab. The thickness of the slab normally depends on the size and the application of the extension. If it is a garage, then it will typically require a thicker foundation. Use a measuring tape to measure the size of the proposed concrete slab and make sure that it's the right size for the room in question.

Step 2 - Excavation

Dig and excavate the area of the foundation slab. Dig down twice the thickness of the slab. If you are going to make a slab which is 3-inches thick, then you will need to dig a hole which is at least 6-inches deep.

Step 3 - Cleaning the Hole

Once you've dug your hole, you need to clean it up. Remove any stones in the hole. Compress the soil by using a compactor. Compactors can be rented from many building companies. Put sand or gravel inside the hole. Doing so helps drainage, which prevents water from disturbing the slab.

Step 4 - Laying a Barrier

A barrier material needs to be laid to protect the concrete flooring. Ding so is especially important if you are laying the concrete foundation inside your house. Barriers are important to prevent moisture from seeping upwards through the concrete flooring.

Step 5 - Making a Frame

Construct a frame made from wood to retain the concrete. Use more sections of wood as screed rails to ensure the floor is level. When doing so, ensure that the wood is straight and not bowed. The frame needs to be complete so that the concrete can't spill out.

Step 6 - Pouring the Concrete

Concrete can be mixed in a cement mixer, then poured into your wooden frame. The screed rails make it possible to level the concrete. Use hand trowels to finish off the job.
Wait for the concrete to set properly. Wait at least 2 months before laying a new hardwood floor. Use a sander to remove high or low spots in the concrete flooring.