DS-04Work out what you're fixing intoFor a floor stop, tap the floor: a dull, dense thud usually means solid concrete or screed, while a slight give or hollow sound means timber boards over joists. For a skirting or wall-fixed stop, trace along the skirting with a magnet or stud detector - a steady line of screw heads every 400-600mm means timber studs behind, and fine steel swarf from a small test hole means metal studs. A hollow, even tap with no give often means dot-and-dab plasterboard over masonry, dense solid-sounding walls are brick or block, and older properties with a slightly springy, uneven surface are often lath and plaster.