DEC-03Fill holes and repair cracks before you paintFill old picture-hook holes and hairline cracks with multi-purpose filler, pressed in with a filling knife and left slightly domed so it doesn't shrink below the surface. On solid brick or block, filler goes on easily — build deep holes up in two thin layers rather than one thick one. On plasterboard, whether it's on timber studs, metal studs, or bonded on with dot-and-dab adhesive, don't overwork or scrub the filler — the paper face tears easily and opens the hole up further. On a lath-and-plaster wall or ceiling, the old lime plaster can be soft; use a flexible filler and press gently, and if an area feels soft or bouncy when you press it, the plaster key has likely failed and needs a plasterer, not filler.