Foundation Cracks in Drywall: What They Mean

The short answer

Drywall cracks from foundation movement usually run diagonally off the corners of doors and windows, are wider at one end, and show up with doors that stick. Straight cracks along a seam are usually cosmetic. If the foundation is moving, have it checked first and fix the drywall after, or the crack comes back.

Why San Antonio walls crack

Much of the San Antonio area is built on clay soil that swells when it gets wet and shrinks when it dries. After a long, dry summer the ground under a slab pulls back, and after heavy rain it pushes up again. The slab moves a little with it, and the walls above crack where they are weakest.

The Balcones Escarpment runs right through the area, and the ground changes on each side of it. To the east and south, in places like Schertz, Cibolo, much of New Braunfels and the east side of San Antonio, the soil is deep, heavy clay. To the northwest, in the Hill Country around Boerne and Helotes, the soil is thinner over limestone, but many lots there were cut and filled to build on, and fill can settle for years.

Foundation crack or cosmetic crack?

The pattern tells you most of what you need to know:

• Likely foundation movement: diagonal cracks running up from the corners of doors and windows, cracks wider at the top than the bottom (or the other way around), doors and windows that stick or will not latch, cracks that keep getting wider, and matching stair-step cracks in brick outside.
• Likely cosmetic: a straight crack along a taped seam, nail or screw pops in a row, hairline cracks in fresh texture, and a straight crack along the ceiling line that opens every winter. That last one is usually truss uplift, not the foundation.

Not sure? Put a pencil mark at each end of the crack and write the date next to it. If the crack grows past the marks over the next few months, the house is still moving and it is worth calling a foundation professional before any drywall work.

Fix the foundation first, then the drywall

Leveling or lifting a slab moves the walls again. It reopens the old cracks and often opens new ones, and any patch done before the foundation work is lost. The order that saves money is: have the foundation checked, let any foundation repair finish, then repair the drywall once.

If the foundation company says the movement is minor and the house is stable, the cracks can be repaired right away.

How the drywall repair is done so it lasts

Smearing compound over a movement crack fills it for a season. A repair that holds opens the crack up, reinforces it and matches it to the wall:

• Loose tape and crumbling compound are cut out so the repair bonds to solid board.
• The crack is bridged with tape bedded in setting-type compound, which is stronger and shrinks less than the premixed kind.
• Board that is broken, especially at door and window corners, is cut out and replaced rather than patched over.
• The wall is floated flat, the texture is matched, and the whole wall is primed and painted so the repair does not show.

We do not repair foundations. We fix the walls, ceilings, texture and paint after the foundation has been checked or repaired, anywhere from San Antonio to Boerne, Schertz and Cibolo and New Braunfels.