Repair methods
Concrete crack sealing
Should I seal the cracks in my concrete?
Sealing is about water, not strength. A flexible sealant placed in a crack keeps surface water, grit and de-icing salt out of it, and can accommodate the crack opening and closing as the slab moves.
That is a genuinely worthwhile outcome in a freeze-thaw climate, because water in a crack is what widens it. It is not a repair that restores the slab, and understanding that distinction is the difference between a satisfied homeowner and a disappointed one.
What the method is
The crack is cleaned out, and a flexible sealant is placed in it so that the material bonds to both faces and can stretch and compress as those faces move.
Flexibility is the defining characteristic and the reason sealing suits cracks that are still moving. A rigid material in a moving crack fails at its bond line or cracks through itself.
The finish is a visible line. Sealing is not invisible, and colour matching to weathered concrete is approximate at best.
What it does not do
- It does not restore structural continuity across the crack. The two sides remain two sides.
- It does not stop movement, address settlement, or fill a void beneath the slab.
- It does not make the crack disappear. Expect a visible line.
- It does not address why the crack formed, so a crack driven by an active cause will keep moving under the sealant.
What you can safely check yourself
- Establish whether the crack moves seasonally before choosing a material, since that is the variable sealing is designed around.
- Note whether the crack is carrying water, which strengthens the case for sealing regardless of appearance.
- Photograph and measure the crack before it is sealed — once sealed you can no longer monitor it.
When this is frequently cosmetic
- Sealing a stable, dry, fine crack is largely a preventive and appearance choice rather than a necessary repair
When professional evaluation matters more
- There is vertical displacement across the crack, which sealing does not address
- The crack is in a foundation wall or anything carrying load
- The crack is widening measurably, which suggests dealing with the cause first
Questions to ask whoever comes out
- What material are you using, and is it flexible enough for a crack that moves seasonally?
- Are you routing the crack out first, or sealing it as found? What difference does that make here?
- What will it look like when finished, and how closely will it match?
- How long before it needs redoing, and what governs that in this location?
- If the crack keeps moving, what fails first — the sealant or its bond to the concrete?
Where estimates for this commonly differ in scope
These are the places two prices for apparently the same work stop being comparable.
- Sealing as found and routing before sealing are different jobs at different prices with different service lives. Estimates often say only "seal cracks".
- Pricing per crack and pricing per linear foot produce very different totals on a slab with many cracks.
- Whether the whole slab is also being sealed is a separate item that sometimes gets folded into the same line.
Usually worth planning a repair
Conditions in this band do not usually become emergencies, but they rarely improve on their own and repair costs tend to rise with the affected area.
Who tends to do this work
- A concrete repair specialist
- A residential flatwork concrete contractor
ConcreteOwner does not inspect, certify or approve contractors. This describes which trade usually holds this work, not a recommendation of anybody in particular.
Common questions
Does sealing a crack make it stronger?
No, and this is the most common misunderstanding about it. Sealing keeps water and debris out of the crack; it does not restore continuity across it or transfer load. Its value is in preventing the deterioration that water in a crack causes, which is real but different from strengthening.
How long does crack sealing last?
There is no universal figure and anyone quoting one is generalising past the evidence. What governs it: how much the crack moves, the material's flexibility and UV resistance, how well the crack was prepared, exposure to salt and sun, and traffic over it. Ask your contractor which of those they think is limiting in your case.
Should I seal or fill?
Sealing suits cracks that move, because the material can accommodate it. Filling suits cracks that are stable, where a rigid material can restore a continuous surface. The wrong way round is the common failure — a rigid filler in a moving crack breaks, and a flexible sealant where a hard wearing surface was needed wears out.
Where to go next
Worth comparing
What drives the cost
Methods that may apply
Want a straight answer about crack sealing?
Both decision tools are free and need no contact details. If you would rather have somebody local look at it, you can ask us to review whether we can match you — and we will say plainly if we cannot.