Your ground floor concrete slab will be ready to be poured once the foundations have been laid and the walls have been built up to damp proof course. Before the epic pour, there are a few key stage preparations that need to take place.
1) Compression If hardcore (or more commonly a Type 1 floor seal) is in place, this must be compressed before work can be carried out.
2) Sand blinding – If hardcore has been used, sand blinding will need to take place next. Building sand is shovelled into the area where the slab is being poured, then its distributed and levelled off. The sand will fill any bumps and hollows, and a thickness of around 50mm is usual once tamped down.
3) DPM -Damp Proof Membrane goes down. Thicknesses of DPM’s vary, but 1200 gauge is a common thickness. It is preferable to cover the area with one large sheet, but in cases where more than one sheet is required, joins should overlap by at least 150mm, and be sealed to prevent any moisture coming up through the concrete slab. The edges of the DPM will go up the walls and wrap over the brick walls, and eventually sit under the next course of bricks.
This is poorly shown below. In the first picture, you can see the DPM scrunched up, but eventually it will be pulled out, cavity cleaned and then wrapped around the brick wall. In the second picture again, the detail is poor and not a good example of how it should be. Constructions never straight forward.
4) Pour & reinforcement – Then comes the concrete, which, on larger sites is pumped directly into place, typically 100mm. It will take around 3 days to cure. The metal mesh which can be seen in the picture is used to reinforce the concrete, & as it’s a ground floor slab should be sitting on plastic/concrete spacers giving a minimum of 75mm cover.
5) Insulation – Once the concrete is levelled and has set, the insulation goes down, which is usually 75-100mm of rigid foam board.
6) Vapour barrier – Finally, many people choose to put down a vapour barrier on top of the insulation before screed is poured. Any pipe work for underfloor heating is then laid out and secured before the screed is put down. The screed usually takes around 7 days to cure