SK-02Work out what's behind the wallTap along the skirting line: a dull, solid sound usually means brick or block, while a hollow sound suggests a stud wall or dot-and-dab plasterboard. Run a magnet or stud detector along the wall - a line of fixings roughly 400-600mm apart usually marks timber studs, and closer, evenly spaced fixings often mean metal studs. Drill a small 3mm test hole in an inconspicuous spot: fine wood dust means timber, grey powder means masonry or dot-and-dab, and bright metal swarf means a metal stud. Lath and plaster walls feel slightly springy and give a lower, softer knock, with narrow wooden laths under the plaster.