Concrete Slab Step-by-Step
Whether you are casting concrete for foundation footings to support a simple timber structure, or for a solid slab that will form the floor of a garden building to be built from wood, the principles are exactly the same.
Of course, if the slab is to act as a foundation, it must be designed and constructed to carry the load of the brickwork, timber and any other materials used (including the roof structure). Also, the method of construction will affect the size and type of all foundations and footings.
This particular slab was cast to support a timber stud structure and a 75 mm-thick slab was laid on well-compacted fill. Low-strength concrete (cement, sand and stone mixed by volume in the ratio 1:4:4) is suitable for most garden buildings, and it was this mixture that was used.
The National Building Regulations state that a straightforward foundation like this one should be constructed using concrete that has a compressive strength at 28 days of at least 10 MPa. The ratio the regulations recommend is slightly weaker than the one we used, namely 1:4:5.