AB-02Work out exactly what's behind the plasterTrue lath and plaster is always fixed onto timber — thin wooden laths nailed to timber studs on a wall, or joists on a ceiling — never onto metal studs. Tap along the surface: solid, dull thuds mark a stud, hollower sound means you're between them. Confirm with a stud detector or magnet tracking old nail heads, spaced roughly every 400-600mm, and drill one small test hole at a mark — timber dust confirms solid timber. If instead you find neat rows of screw heads and fine steel swarf from the test hole, you're not on genuine lath and plaster but a metal-stud plasterboard wall, and you'll need a self-drilling or toggle metal-stud fixing instead — never a wood screw or plastic plug, which strip straight through 0.5mm steel. If the wall sounds solid all over with no give, it may be brick or block behind a plaster skim — use a plug and screw sized for masonry. A bouncy, hollow sound everywhere with no stud pattern suggests dot-and-dab plasterboard, which needs a long fixing reaching through to the masonry behind.