The photo on the right shows the blockwork and cavity concrete painted with bitumin paint, as part of the Radon protection. The bitumin is continuous with the DPM under the slab and so there is a barrier to Radon right across the house. Tip. When filling the cavity with concrete, leave the top inch and fill this with a sandy mix and trowel smooth - this then leaves a surface that is much easier to paint with the bitumin.

Generally, the internal walls are built after the outside walls are taken to joist level. The internal walls are keyed in by incorporating expanded mesh strips into the beds at each course of the outside walls. Here the strips can be seen projecting out.

Once one or two courses have been laid, a length of straight timber is nailed plumb to the external wall to act as a guide to building the internal wall - quicker than checking each course with a level

If incorporating a brick plinth under a rendered wall, use plastic sheeting to protect the brickwork