Preparation done properly
Why cracks are repaired before coating, not covered by it
A coating is a few thousandths of an inch of resin. It does not bridge a moving crack, and treating it as though it will produces a visible line within a year.
Reviewed by
Houston Superior Epoxy Technical Team
- Published
- Last reviewed
Do cracks need to be repaired before epoxy coating?
Short answer
Yes, as their own step before any coating goes down. A coating film is far too thin to bridge a crack that moves with the slab, so an uncoated crack telegraphs through the finish as a visible line and then reopens. Repair means opening the crack, filling it, and grinding it flush before coating.
Key takeaways
- A coating is thousandths of an inch thick. It cannot span a moving crack.
- Repair is a separate step with its own line item, performed before coating begins.
- Proper repair opens the crack out, fills it, and grinds the fill flush with the slab.
- Houston clay soils drive slab movement, so cracks here are frequently active rather than dormant.
- Control joints are designed to move and are treated differently from cracks — they are not simply filled and forgotten.
Why a coating cannot cover a crack
Coating thickness is measured in thousandths of an inch. A crack in a concrete slab is a structural discontinuity that opens and closes as the slab moves with moisture and temperature. There is no version of a thin resin film that spans that reliably.
What happens instead is predictable: the crack telegraphs through as a visible line, then the film splits along it. The coating did not fail — it was asked to do something no coating does.
What proper repair involves
The crack is opened out to give the repair material a real cross-section to hold, cleaned of debris, filled with an appropriate material, and then ground flush so the surface is continuous.
That last step is the one most often skipped. A fill left proud of the slab shows as a ridge under the finished floor just as clearly as an unrepaired crack shows as a line.
Spalls and pitting are the same argument
A spall is a shallow crater where the surface has broken away. Coating over it produces a coated crater. It gets patched and levelled first, for the same reason.
Grinding often reveals spalls and soft patches that were not obvious beforehand, which is one of the practical arguments for grinding early enough in the process to react to what it finds.
Why this comes up so often in Houston
The expansive clay soils across much of the metro move significantly with moisture, and slabs move with them. That makes cracking common and often active rather than settled.
It also means control joints matter. Joints exist to accommodate movement, and they are handled deliberately rather than simply filled level with everything else.
Terms used on this page
- Spall
- A patch where the concrete surface has flaked, chipped or broken away, leaving a shallow crater. Spalls are repaired and levelled as their own step before any coating is applied.
- Concrete surface profile (CSP)
- The ICRI scale describing how rough a prepared concrete surface is, from CSP 1 (nearly smooth) upward. Coating manufacturers name a target CSP in their data sheets; diamond grinding is how that profile is produced repeatably.
The service this applies to
Garage floor crack & spall repairRelated completed projects
Want this applied to your own slab?
We inspect the concrete, moisture test it, and give you an itemized written quote. The visit is free.
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- 5-year workmanship warranty
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