TS-03Prepare the surface and fit backer board where neededBefore drilling anything, know where your stopcock is (usually under the kitchen sink) and check it turns, in case you hit a pipe. Use a detector but still treat every spot as if a cable or pipe could be there — detectors miss cables in metal conduit, behind metal-backed board, or deep in the wall. On solid brick or block that's sound and flat, you can often tile directly; on plasterboard over timber studs, fit cement tile backer board with 40mm decking screws driven into the centre of each stud. On metal studs, use self-drilling wallboard screws made for steel — an ordinary wood screw strips straight through 0.5mm steel. On dot-and-dab, avoid heavy backer boards unless upgraded — screw through the plasterboard and dabs into the masonry behind using a fixing long enough to bridge the gap, typically 60-75mm. On lath and plaster, the laths won't hold a fixing at all — strip back to the joists and fit new board screwed into solid timber.