How to Repair Cracks in Drywall So They Stay Repaired

Filler alone will not hold. A crack that reopens was never reinforced properly.

Cracks in plasterboard almost always appear along a joint or at a stress point such as a door corner, and they reopen because the movement that caused them has not stopped. Simply pressing filler into the gap gives a repair that looks perfect for a season and reappears the following winter. A durable repair requires reinforcement bridging the crack, embedded in compound rather than sitting on top of it.

The Method That Actually Holds

Rake out the crack slightly with a utility knife to remove loose material and give the compound something to key into. Apply a thin bed of joint compound over the crack, press paper tape or self-adhesive mesh into it, then bed it flat with a broad knife so almost no compound remains under the tape. Let it dry fully. Apply two further coats, each wider than the last, feathering the edges out 150 to 200 mm either side. Sand lightly between coats, and resist the urge to build the whole thickness in one pass; thick compound shrinks and cracks as it dries.

At door and window corners, where diagonal cracks are common, the underlying cause is usually a board joint landing exactly at the opening corner. If the wall is being reboarded, arrange the sheets so no joint aligns with a corner. If it is not, mesh tape and patience are what you have.

When the Crack Is Telling You Something Else

A hairline crack that follows a joint is cosmetic. A crack wider than about 3 mm, one that runs diagonally across a wall independent of the boards, or one that keeps widening, is structural movement and filling it hides a problem rather than solving it. Note the width, mark the ends with a pencil and a date, and check it again in a few months. If it has grown, get the cause investigated before decorating over it.

Summary

Rake, reinforce with tape, then build up in thin feathered coats and prime before painting. Reserve concern for cracks that are wide, diagonal or growing. Our Drywall Calculator covers board and compound quantities if the repair turns into a reboarding job.