Yes, but not directly over the crack. Epoxy is a rigid coating that follows whatever is underneath it, so a crack left untreated will telegraph straight through the finished floor — usually within the first year, sometimes within weeks. Cracks have to be routed out, filled with a structural repair material, and, most importantly, understood before anything is coated.
That last part is what separates a repair that holds from one that fails. A crack that has stopped moving can be filled and coated over with confidence. A crack that is still moving will reopen through any filler you put in it, and the only real fix is addressing why it is moving.
Why Coating Straight Over a Crack Fails
Epoxy cures hard. It has very little capacity to stretch, so when the concrete beneath it moves, the coating cannot absorb that movement — it splits.
Two things then happen. The crack becomes visible again through a floor you just paid to finish. And the split gives moisture and contamination a route underneath the coating, where it spreads sideways along the bond line and lifts the epoxy well beyond the original crack.
A hairline crack ignored at preparation stage routinely becomes a delaminated area several times its size a year later.
First, Work Out What Kind of Crack You Have
They look identical and behave completely differently.
Dormant cracks
These have finished moving. Most are shrinkage cracks formed as the slab cured — concrete loses volume as it dries, and it cracks where it is restrained. Once that shrinkage is complete, the crack stays put.
Dormant cracks are routine. Route, fill, coat, and the repair holds for the life of the floor.
Active cracks
These are still moving, driven by something ongoing:
- Settlement — the ground beneath the slab consolidating unevenly
- Thermal movement — expansion and contraction, significant in Toronto garages and unheated spaces that swing from below freezing to well above 25°C across the year
- Structural loading — the slab flexing under weight it was not designed for
- Water — drainage problems washing out support beneath the slab
Filling an active crack without addressing the cause relocates the problem by a few centimetres. The repair material is stronger than the surrounding concrete, so the movement simply finds a new line alongside it.
Telling them apart
Not by looking. Crack monitors fitted across the crack and read over several weeks show whether movement is ongoing. In a garage or basement, a simpler indicator is whether a previous repair in the same location has already cracked again — that answers the question.
Any contractor who declares a crack dormant on a first visit is guessing.
How Cracks Are Properly Repaired
Route the crack. The crack is opened out with a crack chaser to a consistent width and depth, creating a channel with clean faces. This matters because repair material cannot penetrate a hairline gap — filling an unrouted crack leaves material sitting on the surface with no bond depth.
Clean it out. Vacuum extraction removes dust and debris. Blowing it out with compressed air just redistributes dust into the channel you are about to fill.
Fill with structural material. An epoxy or polyurea crack filler bonds to both faces and restores continuity. Flexible sealants are the wrong choice here — they compress under load and do not restore structural continuity.
Grind flush. The repair is levelled with the surrounding slab so the coating goes down over a continuous plane.
The Other Damage That Has to Be Fixed First
Cracks are rarely the only issue on a floor bad enough that you are asking this question.
Spalling and pitting. Broken-away areas are cut back to sound concrete with square edges and filled with repair mortar. Feather-edged patches — thin material tapering to nothing at the perimeter — have no strength and break away almost immediately.
Surface dusting. If the surface powders under your hand, the top layer has lost cohesion. Coating over it bonds the epoxy to loose material rather than to the slab, and it delaminates in sheets. Grinding removes the failed layer until sound concrete is reached.
Oil and grease contamination. Common in garages and workshops. Contaminated concrete will not accept a bond regardless of surface cleaning, because the contamination has soaked in. Mechanical removal is the only reliable answer — grinding down until clean concrete is exposed.
Previous coatings. Old paint or a failed epoxy layer has to come off mechanically. Coating over a failing coating inherits its failure.
Test for Moisture Before Anything Else
This causes more epoxy failures in Toronto basements and slab-on-grade garages than cracks do, and it is invisible.
Concrete slabs transmit water vapour from the ground beneath. Where that vapour pressure builds under an impermeable coating, it lifts the film — producing bubbling and blistering months after an installation that looked perfect.
Moisture vapour emission testing before installation tells you what the slab is doing. Where readings are high, a moisture mitigation primer goes down first. It adds a step and it is the difference between a floor that lasts and one that fails through no fault of the epoxy.
Preparation Is What Makes It Hold
Once repairs are complete, the whole floor needs mechanical preparation — diamond grinding or shot blasting — to open the concrete profile so the coating keys into it.
Acid etching is the shortcut here, and it is the leading cause of coating failure. It does not produce a reliable profile and it leaves residue that interferes with adhesion. If a quote specifies acid etching rather than mechanical preparation, that is worth questioning. Our approach to concrete floor surface preparation in Toronto exists for exactly this reason.
When the Floor Is Too Far Gone to Coat
Sometimes repair-then-coat is not the right answer.
Where damage is extensive rather than localised — spalling deeper than a few millimetres across much of the floor, or a surface that only reaches sound concrete at significant depth — patching each defect stops making economic sense. Resurfacing rebuilds the wearing surface instead. We cover that threshold in when a concrete floor needs resurfacing instead of coating.
Where the slab has structural cracking through its full depth or is settling because the ground beneath has failed, no surface treatment will help.
Common Toronto Situations
Garages. Usually the worst residential slab in the house — road salt, freeze-thaw cycling, and vehicle loads. Expect cracking and surface scaling, and expect them to be repairable. See epoxy garage flooring in Toronto.
Basements. Moisture is the dominant issue rather than cracking. Test before you coat.
Commercial and industrial floors. Joint spalling usually matters more than field cracking. That is covered separately in repairing a damaged warehouse concrete floor.
Getting It Assessed
Whether your cracks are dormant, how deep the surface damage runs, and what your slab moisture is doing are all questions that need someone looking at the floor.
Armour Guard has prepared and coated concrete floors across Toronto and the GTA for more than 30 years, including plenty that other contractors said were beyond coating.
Contact our Toronto team for an assessment of what your floor needs before it is coated.