TW-03Check the wall can take the weight, and fix support safelyLarge-format tiles are heavy, so weak walls need reinforcing before you start. Cables and pipes can run almost anywhere behind a wall - always use a detector, but still assume something is there until you've proved otherwise, since detectors miss deep cables, metal conduit, and anything behind metal-backed board. Find your stopcock (usually under the kitchen sink) and check it turns before you drill, so you can shut the water off fast if you hit a pipe. If you have any doubt, isolate the circuit at the consumer unit first, and turn off the water before cutting into anything that might carry it. On a timber stud wall, screw a cement backer board into the centre of each stud with a wood screw. On a metal stud wall, use self-drilling metal-stud screws or a toggle fixing - never a wood screw or plastic plug, both strip straight through 0.5mm steel. On dot-and-dab, use a fixing long enough to pass through the plasterboard, the dab gap and bite into the masonry behind - usually 60-75mm. On lath and plaster, avoid fixing into the lath itself; find the joists or studs behind it instead, or overboard with plasterboard first. If a metal stud wall has no timber noggin behind it, don't rely on it alone for a heavy tiled area - fix through to solid masonry or add a noggin first.