PIC-02Work out what the wall is made of and what's behind itKnock along the wall — solid brick or block sounds dull and dense, plasterboard sounds hollow. Run a stud detector or magnet along your marked line to track screw heads and find studs; a line of hollow sound between studs with solid hits every 400mm or 600mm means a stud wall. Drill a small pilot hole at a proposed fixing point: pale timber dust means a timber stud, fine grey swarf means a metal stud, and dust with no resistance change usually means plasterboard between fixings or dot-and-dab. Cables and pipes can run almost anywhere in a wall, so use a detector but still assume something might be there — detectors miss cables that are deep, in metal conduit, behind metal-backed board, or outside the usual safe zones, and a metal stud frame can confuse a cheap detector further. Before you drill, find your stopcock (usually under the kitchen sink) and check it turns freely, so you can shut the water off fast if you hit a pipe; if you have any doubt, isolate the relevant circuit at the consumer unit first, and turn the water off at the stopcock before cutting into anything that could carry water.