PJ-05Re-fix a loose board before fillingIf the board itself moves or sounds hollow right at the crack, screw it back to the structure first, or the crack will return. Into a timber stud, use a 38mm coarse-thread woodscrew driven into the centre of the stud, within 150mm of the crack. Into a metal stud, use a self-drilling metal-stud screw of the same length - never a wood screw or a plastic wall plug, both strip straight through 0.5mm steel. On dot-and-dab, use a screw long enough to reach the masonry behind the board, typically 60-75mm with a suitable plug, since fixing into the board alone won't hold. On lath and plaster, screw through into the timber joist or stud behind the laths, not into the plaster - the laths alone won't hold a fixing.