Reading your slab: 7 foundation warning signs on WilCo clay

On Central Texas clay, some cracking is normal and some is the start of a real problem. Here’s how to tell the difference before you spend a dollar.

1. Stair-step cracks in exterior brick

Cracks that climb the mortar joints in a diagonal staircase pattern — usually starting near a corner, a window, or a garage opening — are the classic sign of differential movement. What matters isn’t how wide it is — it’s whether the brick coursing has stopped being level across the crack, and whether it’s grown since last year. Either of those is worth an assessment. (Why width alone doesn’t decide it →)

2. Diagonal cracks from the corners of doors and windows

Inside, look for cracks running at roughly 45 degrees out of the top corners of door and window frames. Those corners are stress points; when the slab moves, that’s where the drywall tears first. Straight vertical hairlines over a door are usually just drywall shrinkage — the diagonal ones are the ones to note.

3. Doors and windows that stick seasonally

This one is very Central Texas: interior doors that jam by late summer and swing free again after the winter rains. That seasonal rhythm is the clay swelling and shrinking, flexing the door frame out of square. If a door has stuck and stayed stuck, or several doors go at once, the movement may be more than seasonal.

4. Gaps at the baseboards or where walls meet the ceiling

A gap opening up between the baseboard and the floor, or a separation where the wall meets the ceiling, means the frame is being pulled apart by movement below. Caulk that keeps cracking back open in the same spot is telling you the same thing.

5. Sloping, sagging, or bouncy floors

Set a ball or a marble on the floor — if it consistently rolls to one side of a room, you may have real elevation change. Bouncy or spongy floors are more common over pier-and-beam (a sign of failing supports or rotted wood below), while a hard slope on a slab points to settling.

6. Cracks in the slab itself or the garage floor

The garage is often the easiest place to read a slab because the concrete is exposed. Fine curing cracks are normal; a crack with a vertical lip you can feel with your foot — one side higher than the other — means the two halves have moved relative to each other. That’s worth attention.

7. Separating trim, cabinets pulling from the wall, or a chimney tilting

Crown molding opening at the seams, kitchen cabinets drifting away from the wall, or an exterior chimney leaning slightly away from the house are all “the structure is racking” signs. A tilting chimney in particular is worth a prompt look.

How wide is too wide? Width, direction, and the quarter-inch rule

The first question everyone asks about a crack is how wide it can be before it’s serious. A common rule of thumb says a crack wider than about a quarter inch (roughly the width of a pencil) is worth a professional look — and that’s a fine screening line. But width is the least reliable thing about a crack. Direction tells you more, and change over time tells you most.

• Vertical cracks — running straight up and down, often over a doorway or in drywall seams — are usually the least worrying. They’re frequently drywall shrinkage or minor settling. A hairline vertical crack that never changes is rarely structural.
• Diagonal cracks — especially at roughly 45 degrees from the corners of doors, windows, or garage openings — point to differential movement, one part of the slab dropping relative to another. These earn an assessment even when they’re thin.
• Horizontal cracks — running sideways across a wall, or along a block or brick course — are the ones to take seriously fastest. In a wall they can signal pressure pushing in, not just settling down.
• Stair-step cracks in brick or block follow the mortar joints diagonally; see sign #1 above. Watch whether the courses have stopped being level across the crack.

Here is the honest part the quarter-inch rule leaves out: a stable quarter-inch crack that hasn’t moved in five years can be less urgent than a hairline diagonal crack that doubled last summer. On Central Texas clay, the real signal isn’t any single measurement — it’s change over time. Mark the end of a crack with a pencil and a date, photograph it, and check it across a wet season and a dry one. A crack that keeps growing is telling you something a one-time width reading never will. The crack checker walks you through exactly this in six questions, and gives you a printable log to track the width and date yourself.

What to do if you’re seeing the pattern

Note which signs you have and roughly when they started (a photo timeline helps), and mention whether you’re on a slab or pier-and-beam when you request quotes — that routes you to the right kind of crew. You can also check the honest cost ranges first so a quote doesn’t catch you off guard, and see why east-county clay moves more if you’re in Hutto, Taylor, or Pflugerville.

Buying or selling a house with these signs?

Texas sellers must complete a disclosure notice, and the form’s wording around foundation work is narrower than most people expect. What has to be disclosed, and what an inspection actually covers →

Quick answers

How do I know if my foundation is bad?

Look for the pattern, not a single crack: stair-step cracks in exterior brick, diagonal cracks running from the corners of doors and windows, doors and windows that stick seasonally, gaps at the baseboards or where walls meet the ceiling, and sloping or bouncy floors. One hairline crack is usually cosmetic; several of these signs together — especially if they’re widening over months — is the pattern worth having looked at.

Is a crack in my foundation serious?

Width and direction are the tells. Hairline vertical cracks are common and usually cosmetic. Cracks wider than about a quarter inch, cracks running on a diagonal from door and window corners, and horizontal cracks are the ones to take seriously. The single most useful signal is change over time — mark a crack’s ends and date them; a crack that keeps growing matters more than one that’s simply there.

Foundation repair by city

Soil, neighborhoods and permit rules differ across the county. Local detail for Round Rock, Georgetown, Cedar Park, Leander, Hutto, Pflugerville and Taylor, or see every area we serve.

More foundation guides: Why Hutto & Taylor homes crack more · Watering your foundation through a Texas drought