Problems
Cracked concrete
There is a crack and you do not know whether to worry.
Concrete cracks. It shrinks as it cures, expands and contracts with temperature, and has very little tensile strength, so it relieves stress by cracking. Control joints exist precisely because cracking is expected: they are deliberate weak lines that decide where it happens.
So the question is never whether there is a crack. It is what the crack is doing.
The four things worth checking
Width tells you least on its own, though very wide cracks are worth more attention. Vertical offset — whether one side sits higher than the other — tells you a great deal, because it means the two sides are no longer supported the same way. That is movement, not cracking.
Growth matters more than size. A stable half-inch crack and a growing quarter-inch crack are different problems, and the growing one is the more interesting. Water matters because water in a crack moves the material underneath it and, in freezing climates, expands inside it.
- Is one side higher than the other?
- Is it getting longer or wider?
- Does water run into it, or across it?
- Is there settlement visible nearby?
Patterns and what they usually mean
A crack that follows a control joint is the joint doing its job. A single straight crack across a panel is very common and usually a shrinkage or temperature response. A fine map or spiderweb pattern across the surface — sometimes called crazing — is typically a finishing and curing effect confined to the top layer.
Branching cracks, cracks that pass through several panels along a consistent line, and broken-off corners are the patterns that more often indicate something underneath. None of these is a diagnosis; they are reasons to look further.
How to monitor properly
Draw a pencil line across the crack at each end and date it. Photograph the crack next to something for scale, from the same position. Repeat in a month or two, and particularly after heavy rain.
This costs nothing and answers the one question that changes the decision. Contractors take it seriously when a homeowner arrives with dated photographs.
What to ask a contractor
- Do you think this crack is stable or still moving, and what are you basing that on?
- Is a repair here worth doing, or is it treating a symptom?
- What would you fill it with, and how will it look afterwards?
- Is there anything about drainage you would change first?
Common questions
How wide does a crack have to be before it matters?
There is no single threshold that applies across every situation, and any page that gives you one is oversimplifying. Behaviour matters more than width: a narrow crack that is growing, or that has a height difference across it, is more informative than a wide one that has been static for a decade.
Should I fill cracks myself?
Filling a crack to keep water out is a reasonable homeowner job on stable cracks in flatwork, and in freezing climates it is worth doing. What it does not do is address movement — and filling a crack makes it harder to tell whether it is still moving, so photograph and mark it first.
Do cracks mean the concrete was poured badly?
Not necessarily. Some cracking is inherent to the material. Cracking that appears very early, runs in a pattern unrelated to the joints, or is accompanied by surface problems can point at mix, placement, curing or jointing decisions — but plenty of well-executed concrete cracks too.
Work it out, or judge the quote
Related guides
Common concrete problems
Start here: match what you are seeing to what it usually means and what it usually needs.
Read more →Concrete settlement
The process behind sunken slabs: why ground loses volume and what makes it stop.
Read more →Spalling concrete
Surface breaking away in chunks, often with aggregate showing — usually water, freezing and salt.
Read more →Repair or replace?
The central question: when repair holds, when it is money spent twice, and how to tell.
Read more →Sealing and coatings
Sealers, epoxy and garage-floor systems: what they protect against and what they do not.
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