Q.
Describe the concrete flooring commonly used for construction of ground flooring.
A.
Concrete floors
Concrete floors give us the most options in terms of floor finish because so many different materials can be laid on top of concrete. They can be constructed on the ground or to form upper storeys, above the ground. The specifications will differ depending on where the slab is to be constructed.
Ground floor concrete slabs
When working at ground floor level, once the foundations have been placed, a slab is constructed according to the specifications of the architect or engineer, or at least to the specifications given in SANS 10400 that explain how to comply with the building regulations. These specifications say that a concrete slab must have a compressive strength of not less than 10 MPa at 28 days, or be mixed in the proportions by volume of one part cement, four parts sand and five parts coarse aggregate (which is usually crushed stone). The thickness of the slab should be at least 75 mm.
Remember that the strength of concrete is measured in megapascals (MPa) which are the recognised units used to measure the strength of materials. Any contractor or supervisor who isn’t sure about concrete specifications should consult a concrete technologist for advice.
The earth underneath the concrete slab will need to be well compacted before the damp proof course (DPC) is laid. Then the concrete can be placed. Ground slabs shouldn’t rest on any part of the foundation walls. They are usually separated from the brickwork so that they can move without cracking.
Also, a slab shouldn’t extend over the internal foundations that support internal walls. It is much better to lay the slab between the foundation wall of each room. In all instances floor slabs must be allowed to cure thoroughly before the floor is screeded and floor coverings laid.
It is also possible to construct suspended concrete floors by using a precast product, for example the popular beam and block system.
Whichever construction method is used, it is usual to leave concrete surfaces quite rough to provide a key for the cement-sand screed.