How to Lay a Concrete Foundation

Laying a foundation before undergoing any structural work is an absolute must. The foundation is there to take and spread the forces applied by the above structure. it goes without saying that all foundations will vary in shape and size, but for the purpose of this exercise we will concentrate on a foundation for a straight wall one skin (100mm) thick. This how to shows you how to do it safely and well. 

Photo Credit: Designlazy.com

Steps

1) Once the desired location for the foundation has been determined, using either spray paint or paint, mark out the area that is to be excavated. Bear in mind that if the foundation is to carry a brick or block wall it must be at least roughly 300mm wider than the centre line of the wall. Using a combination of a pick and shovel excavate the painted area, bearing in mind that services such as pipes and electrical cables may run underneath. 

2) If the excavated area has naturally formed barriers or walls such as earth, then it is possible to pour the foundation without forming a framework. Lets assume that this isn’t the case. Cut lengths of plywood to the required length and depth, use whole lengths where possible. The framework will form the perimeter of the foundation and must be strong enough to support the poured concrete. Props can be fixed to the external sides of the framework from small lengths 100mm x 50mm timber nailed into place. Concrete blocks are also effective in providing extra support if you happen to have any at your disposal. 

3) Concrete can either be mixed on location or ordered. When mixing on location the amount of concrete needed is relatively easy to judge as the it can mixed until the framework or area is full. If concrete is to be ordered then the volume required needs to be calculated. 

4) To ensure the foundation is level without using any complicated and unfamiliar machinery, simply hammer lengths of rod into the soft ground and then use a spirit level. Using a spirit level, level across to each rod and ensure they are at the height. 

5) The concrete can now be poured into the framework or the excavated area. Fill the entire area and move a length of timber about the concrete to help move it into all areas.  To achieve an even finish to the surface of the concrete, take a length of timber end drag it over the concrete pulling away any excess or adding to in the process. Your finished height will be indicated by your rods.

Tips

Ensure the foundation is both wide enough and deep enough

The framework must be well supported

Work the concrete so it reaches all areas of the trench

Use height rods to achieve a level finish.