Do Concrete Crack Fillers Really Work?
Updated October 2026
A concrete crack filler fails on a crack that is wide, growing, or sitting beside a dip. A filler treats the opening, not the cause. If the base is washing out or the slab is moving, the crack reopens, often by spring. Before you buy a tube, find out what the crack is doing. If you are not sure, a free written assessment will tell you.
It is fair to ask whether crack filler works. The honest answer is that it depends on the crack. A filler can be a patch that fails by spring. This guide shows how to tell which one you have.
What a crack filler does, and does not do
A filler fills the opening. It does not stop a crack from moving, and it does not fix whatever caused the crack.
That is the whole problem. Caulk smeared into a moving crack opens by spring. Patches that ignore the cause, such as a washed-out base, a downspout dumping beside the slab, or clay heaving under a corner, do not last.
Cracks that may not need more than a watch
- A narrow crack that stays put. Hairlines under 1/8 in. that do not change are normal concrete behaviour.
- A crack in a level slab that looks the same season to season. Nothing has sunk and nothing is moving.
Check the product’s label before you buy, because “crack filler” on its own does not say what it is made of or what movement it can take.
Cracks where a filler will not hold
- A crack that keeps widening. Cracks wider than 1/4 in., or cracks that widen each season, mean the base or the soil is moving.
- A crack with one side higher than the other. Something under the slab has shifted. See our guide to why a driveway or slab sinks.
- A crack that leaks. In a basement wall, the fix is water management. See epoxy vs polyurethane crack injection.
Why the filler type matters
Epoxy is rigid. It needs a dry crack that is not moving, and if the wall shifts after it sets, the crack can open again beside the old line. Polyurethane stays flexible and foams to fill a damp crack, so it can follow seasonal movement. A crack that opens a hair in winter and closes in summer does not break a flexible seal as easily as a rigid one.
How to test before you fill
- Take photos with a coin or ruler beside the crack, and note the date.
- Look again after a freeze-thaw cycle. If the crack is wider or one side has moved, it is not a filler job.
- Check the surface around it. A dip, a puddle or a downspout nearby points to the cause.
Our post on spring concrete crack inspection shows what to check each year, and our guide to cracks in a new driveway covers the normal ones.
When a proper repair is the better spend
A sound slab with a stable crack can often be repaired by injecting the crack to full depth. A slab that has settled can be levelled. A slab that has cracked into a road map needs removal and a fresh pour. Whether you are weighing repair or replacement, the first step is the same: find out why it cracked.
Get it looked at
You do not have to guess. We will look at the crack, the base and the drainage, and tell you plainly whether a filler is enough or the crack needs real work. The written quote is free, and we reply within one business day. Learn more about concrete repair and resurfacing.
Do concrete crack fillers really work?
Only on the right crack. A filler does not work when the crack is moving or when something underneath is causing it, because the crack opens again beside or through the filler.
Why does crack filler keep coming out of my driveway?
Usually because the crack is moving. Caulk or filler smeared into a moving crack opens by spring. Ontario freeze-thaw cycles open and close a crack through the winter, and a rigid or thin filler cannot follow that movement.
Which cracks are too big for a filler?
Watch any crack that is growing. Hairlines under 1/8 in. that stay put are normal concrete behaviour. Cracks wider than 1/4 in., cracks that widen each season, or cracks where one side sits higher than the other mean the base or the soil is moving, and filling the surface will not stop it.
Is epoxy or polyurethane better for a concrete crack?
It depends on what the crack is doing. Epoxy is a rigid resin that needs a dry crack that is not moving. Polyurethane is flexible and foams to fill a damp crack, so it moves with the seasons. A tube of filler from a store does not tell you which one it is, so check the label for what it is made for.
Does the warranty cover a crack I filled myself?
Our lifetime warranty on labour covers our own workmanship. It does not cover hairline cosmetic cracks or work someone else did. If you are unsure whether a crack is cosmetic, ask us for a free written assessment.