Cracks that keep growing

Yes — more than anything else on this site. Of all the things you can observe about a crack, whether it is changing is the one that carries the most information, and it is the one almost no search result helps you establish because it needs two observations separated by time.

A stable crack, whatever its width, has finished doing whatever it was doing. A crack that is still moving has not, and repairing it without understanding why tends to produce a repair that cracks in the same place.

What it is

Growth comes in three forms and they are worth distinguishing. A crack can lengthen, extending further across the slab or wall. It can widen, with the faces moving further apart. Or the two sides can displace, with one moving higher or further forward than the other.

They do not always occur together, and they do not mean the same thing. Lengthening suggests the stress is still finding new material to fail through. Widening suggests continued separation. Displacement suggests differential support or pressure, and is generally the one that changes the conversation most.

Seasonal opening and closing is a fourth pattern and is different again. A crack that opens every winter and closes every summer is responding to cyclical movement rather than progressing, and that distinction matters for choosing a filler that can survive it.

What seeing this cannot establish

• Growth establishes that something is active. It does not establish what, how serious it is, or how it ends.
• Casual impressions of growth are unreliable, and honestly so. Cracks look wider when wet, when lit from the side, and when you have been worrying about them. This is why marked and dated measurement matters rather than memory.
• Rate of growth cannot be extrapolated. A crack that moved a millimetre this year will not necessarily move a millimetre next year, in either direction.

What this can be associated with

Candidate explanations, not findings. Nobody can establish which applies to your concrete without seeing it.

• Ongoing loss of support beneath a slab, which can be associated with water moving fine material out of the base
• Seasonal soil moisture cycling, which can open and close a crack without anything progressively failing
• Freeze-thaw action at the crack faces, which can be associated with progressive widening in a climate that cycles
• Continuing settlement or consolidation beneath a footing or slab
• Root growth beneath or beside the element, which continues as the tree does
• Thermal cycling in a long slab with joints that are not accommodating the movement

What you can safely check yourself

• Mark across the crack with a pencil line at a fixed point and write the date beside it. Marking across the crack, not along it, is what makes widening visible.
• Mark both ends of the crack and date those too. Lengthening is often easier to see than widening.
• Photograph from a repeatable position. Note a landmark — a joint, a downspout, a fence post — so you can stand in the same place months later.
• Include a rigid scale in every photograph. A coin works; a tape measure is better; a paper ruler taped beside the crack and left in place is best of all.
• Photograph at the same time of year as well as at intervals. A comparison between February and August in the same year may show seasonal movement rather than progression.
• Write observations down. "Wider than it was" is not evidence; "3 mm at the pencil mark on 14 March, 4 mm on 2 September" is.

When professional evaluation matters more

• Two dated measurements at the same point differ, and the crack is in a wall, a retaining wall, or anything carrying load — this is an engineer question
• One side has become higher or further forward than the other since you first looked
• The crack has lengthened past a dated mark
• Growth has been rapid — visible change over weeks rather than seasons
• Growth coincided with excavation, a plumbing leak, tree work, or an unusually wet season, any of which is worth telling an assessor
• New cracks have appeared nearby while the original one grew

Evidence worth having before you ask for estimates

Every item here is something you can produce without tools or risk, and every one of them makes an estimate more accurate.

• At least two dated measurements at the same marked point
• At least two dated photographs from the same position with a scale in frame
• Dates for when the crack was first noticed and when growth was first noticed
• A note of anything that changed on the site in that period — drainage, landscaping, excavation, heavy vehicles, a leak
• Whether the change was gradual across seasons or sudden

Questions to ask whoever comes out

• Given that this is still moving, does your repair assume the movement stops?
• What would you use here that can accommodate continued movement, and what are its limits?
• Should we monitor further before repairing, and for how long?
• If we repair now and it reopens, what would that tell us and what would come next?
• Is the cause something you can address, or does something else need to happen first?

Where estimates for this commonly differ in scope

These are the places two prices for apparently the same work stop being comparable.

• A repair that assumes a stable crack and a repair designed for a moving one use different materials and cost differently. Estimates rarely state which assumption they made — ask.
• "We'll monitor it" can mean a scheduled return visit with measurements or can mean nothing at all. Establish which.
• Where movement is ongoing, addressing the cause and repairing the crack are separate scopes and may be separate trades.

Who tends to do this work

• A licensed structural or geotechnical engineer
• A concrete leveling specialist
• A concrete repair specialist

ConcreteOwner does not inspect, certify or approve contractors. This describes which trade usually holds this work, not a recommendation of anybody in particular.