GROUNDWORK: preparing the floor slab

The floor slab or "oversite" was a much more complicated piece of construction than I would have imagined. Basically it is lots of specific layers. We would need: 150 mm of hardcore, 50 mm of sand, 1200 gauge membrane (plastic sheet), 100 mm concrete slab, 85 mm insulation, 60 mm screed and then, finally, our tiled surface. The purpose of the sand is to protect the plastic sheet from puncturing on the hardcore. We would need to dig out the floor area to allow for all these layers. The broken up concrete could be recycled for the hardcore layer.

June 2008: My depth guage for digging out the floor slab.

The prep for this has to be inspected before you put in the main concrete layer to make sure you have the correct thicknesses and damp proofing. Later there will be another inspection for the floor insulation. There are various options for how you go about this in Section C of the regs including diagrams of the layer order. There also might be some extra requirements for hazardous contamination and ground gases such as methane. Radon is also an issue in some areas. There are also specifications for what are considered to be suitable materials for hardcore: reasonably clean brick rubble or crushed concrete, carrstones (whatever they are), most other forms of non frost-susceptible stone or rock etc. You can't use: low density thermal blockwork, timber and other similar waste, plaster, clays and silts, topsoil, peat. Most of this stuff is common sense. It's hardcore, so use something hard.

June 2008: I broke up the old drive and used the rubble as hardcore as I went along.

June 2008: The hardcore layer is in place and levelled to the correct depth. The orange duct is to give an optional position for a new water main.

June 2008: The sand layer is installed to protect the damp proof membrane from the puncture.