How do I keep drywall patches from cracking again?

A drywall patch stays shut when you do four things: fix the cause before you fill, bridge the crack with tape, build the repair in thin coats that dry fully, and prime before you paint. Skipping any one of them is how a neat patch turns into a hairline crack by the next winter.

Fix what opened the crack first

A patch cannot hold a board that is still moving. USG says all gypsum panels should be tight and secure against the framing members or underlying substrate, and that loose panels will create “fastener pops” and joint cracks.^[1] Press on the wall beside the crack. If it gives or rattles, screw it back to the studs before you do anything else, and see how to fix nail pops in drywall for the method.

Then look for a reason the wall is wet. A patch over a leak or a damp spot only hides the problem for a few weeks. If you are not sure why the crack opened, read why cracks keep coming back in drywall first.

Tape anything longer than a hairline

Filler alone has no strength across a gap. USG's repair instructions for a large crack are to trim any loose material and wipe clean, apply compound with a knife, then embed paper joint tape in compound to bridge the crack.^[2] Draw the knife firmly over the tape to embed it tightly, and let it dry before the next coat. For a medium hole, USG's instructions are to crisscross two or three strips of paper joint tape over the opening and embed them in compound.^[2]

For a deep crack, open it first. Widen it to remove loose material, creating a groove that is a little deeper and slightly wider than the original crack, then fill.^[3] Deep cracks should be filled in gradually, building up the thickness of the filler material one layer at a time.^[3]

Thin coats, fully dry

Rushing is the next biggest cause of failed patches. USG says to allow each coat of ready-mixed joint compound to dry thoroughly before applying the following coat, so that all shrinkage of the applied coat occurs before the next one goes on.^[1] At 75 °F and 50% relative humidity, allow approx. 24 hr. between applications.^[2]

Dry conditions also matter. Keep the air, the compound and the surface at a minimum of 55 °F within the working area until the joints are completely dry.^[2] Compound that dries too fast, in high heat with low humidity or in a draft, tends to crack along the edge of the tape,^[4] so keep fans and open windows away from a fresh patch. Do not thin the compound with water to make it spread, because USG lists over-thinned compound among the causes of edge cracks.^[4]

A setting-type joint compound, the powder you mix with water, has a head start here. USG says setting-type compounds have the best built-in resistance to cracks.^[4]

Feather wide, sand gently

Do not finish the compound flat and narrow. USG says not to apply joint compound flush or flat to the panel surface, but to use graduated arcs.^[1] In practice that means spreading each coat a little wider than the last, so the patch tapers into the wall and does not leave a ridge that shows under side light.

Sand lightly. Sand with a wet sponge to eliminate dust and scuffing of paper,^[2] or if dry sanding, use 150-grit sandpaper, 220-grit abrasive mesh cloth or finer.^[2] Avoid roughening or damaging the panel face paper when sanding, because the raised damaged fibers may be visible after painting.^[1] Remove all the dust before priming.

Prime, and go easy on corners

Priming seals the filler and helps prevent it from absorbing the new paint.^[3] Unprimed compound soaks up paint differently from the wall around it and shows as a dull patch.

In inside corners, keep the compound thin. USG says to leave only a small amount of compound, or none, in the apex of the angle, and it names excessive build-up of paint as one cause of corner cracks.^[4] Where drywall meets a different material, such as masonry or a wood trim edge, a flexible bead of paintable caulk gives the joint room to move.

For a seam that keeps moving

Some seams move every season. A flexible patching compound suits them. DAP describes its Elastopatch as maintaining flexibility over time, allowing the surface to expand and contract without cracking or crumbling.^[5] The same maker says it is NOT SANDABLE,^[5] so smooth it with the knife and a damp finger or sponge before it sets.

Check the patch after your first heating and cooling season. If a hairline reappears, that is the wall telling you it still moves, and a flexible fill is cheaper than a third full repair.

Stop and call a pro if

• The crack reopens a third time, or keeps widening. The wall is under stress that a surface repair does not relieve, and USG's remedy is to relieve the stress and then retape.^[4]
• The patch stains, bubbles or goes soft. Moisture is behind it. Find the source before you repair again.
• The paint is flaking in a home built before 1978. Any renovation, repair or painting project in a pre-1978 home or building that has lead-based paint can easily create dangerous lead dust.^[6]
• The job has grown past a few patches. Cracks along every ceiling seam, or an entire room, are better handled by a drywall finisher.

Getting help in Virginia

If it is time to hand the job off, read how much a patch and paint job costs in Virginia and whether to hire a painter or a drywall contractor. Browse more painting answers or the painting category.

When you want a pro to do it, describe the wall once and local contractors will quote it.