What this page is and is not. It is a guide to the patterns and what they usually indicate, written so that you can tell a routine crack from one that deserves a proper look. It is not a structural assessment, and we do not make structural determinations from a description or a photograph. Where a pattern warrants assessment we say so plainly rather than reassuring you.
What Direction Tells You
Vertical or near-vertical
Extremely common in poured concrete and usually shrinkage from curing. It may pass water, which is worth injecting, but the crack itself is generally doing nothing else. Monitor the width; if it is stable, it is stable.
Diagonal, from a corner
Typically runs from the corner of a window or door opening and usually reflects settlement. Common and frequently historic. What matters is whether it is still moving — mark it and check in three months.
Stair-step, in block or brick
Follows the mortar joints because those are the weak line. Usually settlement-related. Worth a proper look if it is widening, if one side has moved out of plane, or if it appeared suddenly.
Horizontal, part-way up
The pattern associated with lateral pressure from saturated soil pushing against the wall. This is the one we will not offer an opinion on remotely. It warrants a proper look, and sealant is not the answer to it.
Movement Matters More Than Width
A wide crack that has not moved in forty years is less concerning than a narrow one that has opened measurably since spring. A single look tells you about width; only repeated looks tell you about movement, and movement is the thing.
Mark both ends
A pencil line across each end of the crack, with today's date written beside it. If it extends, you will see it immediately.
Measure the width
At the widest point, with a ruler or a cheap crack gauge from a hardware store. Write the number on the wall next to the date.
Photograph it
With something for scale in frame — a coin, a ruler, a tape measure. Same angle each time.
Check the plane
Run a hand across it. If one side sits proud of the other, that is displacement rather than a simple crack, and it belongs in the assess category.
Look again in three months, and after a wet spring
Seasonal movement is real and informative. A crack that opens during the melt and closes afterwards is telling you something about soil pressure.
The Short List
- It runs horizontally part-way up the wall
- It has widened measurably since you first marked it
- One side sits proud of the other
- The wall is visibly bowing or leaning inward
- It appeared suddenly rather than being noticed
- Doors or windows above it have started sticking
None of those means disaster. They mean the question has moved beyond what a website can usefully answer, and somebody should look at it properly. If any of them apply, that is worth arranging rather than deferring — not because it is an emergency, but because the cheapest version of every foundation problem is the early one.
Crack Questions
Are vertical cracks in poured concrete normal?
Extremely common, yes. Concrete shrinks as it cures and vertical hairline cracking is a routine result. They may let water in, which is worth injecting, but the crack itself is typically not doing anything else. Mark it and check the width occasionally.
Can I fill a crack myself?
Hardware-store patching compounds will cosmetically fill a crack, and they will generally fail at it within a year or two because they do not bond or flex the way an injected resin does. For water entry through a stable crack, professional epoxy or polyurethane injection is the durable answer. For anything in the assess category, filling it is exactly the wrong move — you have hidden the evidence.
My wall looks like it is bowing. What now?
Get it looked at properly. A wall deflecting inward is beyond what we will comment on from a description, and it is the situation where a qualified opinion is genuinely worth having rather than a contractor's reassurance. We would rather tell you that than give you a verdict we are not in a position to give.
Are cracks in a fieldstone foundation different?
Quite different. On dry-laid or lime-mortared stone, what looks like a crack is frequently failed mortar or a displaced stone rather than a fractured wall, and the remedy is repointing with a lime-based mortar rather than injection. What matters on stone is whether soil is washing through between stones and whether anything has shifted position, which is a different assessment entirely.
Does a crack affect selling the house?
It can come up in an inspection, and an unexplained crack is worth more anxiety to a buyer than a documented one. If you have a photographic record showing it has not moved in three years, that is genuinely useful at the table. Which is another argument for marking and dating it now rather than later.