How to read a crack
Four properties tell you most of what you need to know, and you can assess all four yourself before anyone visits.
- Width. Hairline cracks under about 1/16 inch are usually cosmetic. Anything you can fit a coin into deserves attention. Width that varies along the length — wider at one end, tapering at the other — indicates differential movement rather than shrinkage.
- Direction. Vertical cracks are the most common and often the least serious. Diagonal cracks, especially running from the corners of doors and windows, indicate the structure racking. Horizontal cracks in a wall are the most concerning, because they suggest lateral pressure rather than settlement.
- Pattern. Stair-stepping through brick mortar joints is the classic signature of differential foundation movement along that elevation.
- Change over time. The single most useful property, and the one most often not measured. A crack that is the same width next season is telling you something very different from one that has opened.
What each type usually means
| What you see | Usually means | Concern |
|---|---|---|
| Fine vertical cracks in a new slab or wall | Curing shrinkage as the concrete cured | Low |
| Vertical crack, even width, not changing | Historic movement that has stabilised | Low |
| Vertical crack wider at the top than the bottom | Differential settlement below one end | Moderate |
| Diagonal crack from a door or window corner | The frame racking as the structure moves | Moderate |
| Stair-step crack through brick mortar joints | Foundation movement along that elevation | Moderate to high |
| Horizontal crack across a foundation wall | Lateral soil or hydrostatic pressure | High |
| Crack with the two faces offset out of plane | Differential movement with displacement | High |
| Wide crack that appeared suddenly | Rapid change — often a leak or washout | High — act now |
How to monitor a crack properly
The cheapest useful thing you can do
Photograph each crack with a coin or ruler beside it for scale, and make sure the photo carries a date. Repeat from the same position after a seasonal change — after a dry summer and again after a wet spell. Two dated photographs tell an evaluator something no single inspection can: whether the movement is still active.
If you want more precision, mark fine pencil lines across the crack at a fixed point and measure between them, or fit a proprietary crack gauge. Texas movement is seasonal, so a monitoring period that spans a full wet and dry cycle is far more informative than one that spans a month.
Any crack that is widening measurably, or that appeared suddenly, should be looked at rather than monitored. So should any horizontal crack in a wall.
How cracks are actually repaired
Epoxy injection bonds the two faces of a crack structurally. It is appropriate for a structural crack in sound concrete where movement has stopped, and it genuinely restores the tensile capacity of the section. It is not appropriate where movement is ongoing, because the repair is more rigid than the surrounding concrete and the next movement simply cracks beside it.
Polyurethane injection is a flexible foam that seals against water rather than bonding structurally. It is the right answer for a crack that leaks and tolerates minor ongoing movement, which is why it is common on below-grade walls.
Surface sealing and routing fills a crack cosmetically or to keep water out. It makes no structural claim and is appropriate for stable, non-structural cracks.
Carbon fibre reinforcement bonds fabric or strips across a crack to resist further opening. It suits walls under lateral pressure where the cause has been dealt with.
Underpinning. Where the crack is the visible result of the foundation having lost support, the crack repair is the last step, not the first. Slab underpinning or crawl space correction comes before any sealing.
When sealing a crack is the wrong answer
A sealed crack can hide an active problem
If the foundation is still moving, filling the crack removes the most visible evidence without changing anything underneath. Movement continues, and typically reappears beside the repair or somewhere else on the house. Worse, you have lost the gauge that would have told you the movement was ongoing.
Establish the cause before sealing anything structural. That means an elevation survey if there is any pattern of movement, and ruling out an under-slab plumbing leak if the damage is localised. The background on what causes foundation movement in Texas explains why the same crack can mean very different things depending on where in the state the house sits.
Cracks in brick veneer
Brick veneer is not structural — it is a cladding hung on the frame — but it is an excellent indicator, because it is rigid and shows movement clearly.
Stair-step cracking through the mortar joints is the classic signal of differential movement along that elevation. Separation between the brick and a window or door frame, or a visible gap opening between the brick course and the slab edge beneath it, points the same way.
Repointing the mortar restores the appearance. It does nothing about the cause, and if the movement is active the new mortar cracks in the same place. Repoint after the structural question has been answered, not instead of answering it.
What crack repair costs
Crack repair spans an enormous range, because the phrase covers everything from a tube of flexible sealant to a repair that is really an underpinning job with some patching at the end.
Cosmetic sealing of a stable crack is inexpensive. Professional injection of a structural crack is a defined, moderate cost. If the crack is the symptom of a foundation that has lost support, the real cost is the underpinning — see the slab repair page for the published third-party ranges on that work.
We do not quote prices. What we would say is that any proposal to seal a structural crack without first establishing why it opened is worth a second opinion.