PR-04Work out what's behind the wallRun your stud detector along the marked line. A regular change in reading, or a magnet catching on a line of screw heads, means a timber or metal stud wall. A dull, solid knock with no hollow sound means solid brick or block. A bouncy, hollow sound over a slightly uneven surface suggests dot-and-dab or lath and plaster. On a stud wall, drill a small pilot hole at low speed and check the dust - fine pale dust means timber, fine grey swarf means a metal stud frame, which is common in flats and anything built or refitted since the 1990s. Cables and pipes can run almost anywhere, not just in the usual safe zones - a detector helps but can miss cables that are deep, in metal conduit, or behind metal-backed plasterboard, and a metal stud frame confuses cheap detectors further. Find your stopcock now, usually under the kitchen sink, and check it turns freely. If you have any doubt at all, isolate the circuit at the consumer unit before you drill, and turn off the water at the stopcock before cutting into anything that could carry water.