CP-05Cut back plasterboard on dot-and-dab, timber studs or metal studsIf your breast is a boxed-in stud frame or dry-lined dot-and-dab, crumbling plaster usually means the skim has blown from damp or impact damage, not that the board itself has failed. Cut back to a neat rectangle with a sharp knife or plasterboard saw, following the edges of sound board, and remove any damp or soft board back to dry material. Patch with matching-thickness plasterboard (usually 12.5mm), fixed with 35mm drywall screws into the centre of each timber stud, or self-drilling metal-stud screws into a metal frame — never plain wood screws into metal studs, they strip straight through 0.5mm steel. For dot-and-dab, cut back to the dabs, apply fresh dabs of adhesive, and press the patch into place; if you need to fix through the edges for extra strength, use a fixing long enough (typically 60-75mm) to reach through the board and cavity into the masonry behind.