A concrete floor is the slab itself, so its repairs are masonry: cracks are filled, spalls are patched, and the surface is re-polished or resealed. An epoxy floor is a coating on that slab, and its repairs are coatings: chips are filled, worn areas are recoated, and a coating that has come loose in sheets was never bonded and is not repaired but removed. Knowing which of those two you are looking at decides everything on this page.
Hairline cracks in a slab are normal and cosmetic, and they are filled and forgotten. A crack that is wider than a credit card, growing, or with one side higher than the other is the slab moving, and a filler over it is a temporary cosmetic fix over a structural question. A fine web of crazing in polished concrete is surface shrinkage from the pour and is not a defect at all.
Epoxy that has lost gloss, chipped or worn in a traffic lane is repaired and recoated. Epoxy that lifts in sheets, bubbles, or peels off with a putty knife did not bond: the slab was too wet, too smooth, or sealed with something the epoxy could not grip. That coating comes off entirely, the slab is moisture-tested and ground, and a new one goes on — a re-do, not a repair.
DIY a realistic job for a careful person · Hire it the tools or the skill are the job · Replace a repair costs more than it is worth
Shrinkage as the slab cured, settlement, or a control joint that was cut too late. Terrazzo cracks where the slab under it does. The diagnosis, on Why Floors Fail →
A crack that is widening, offset, or accompanied by a sloping floor is a foundation question. Fill it for tidiness if you like, but call a structural engineer first, not a flooring contractor.
Plastic shrinkage at the surface when the slab was poured and finished — too much water in the mix, or a surface that dried faster than the body. Crazing is in the top skin only. The diagnosis, on Why Floors Fail →
Crazing that has turned into spalling — flakes lifting off the surface — is a different failure, usually freeze-thaw or de-icing salt, and that is a resurfacing.
A dropped tool, a dragged jack, a hot tire pulling a soft residential coating, or salt that ate through one spot.
Chips and spalls across a garage floor that started at the tire tracks are hot-tire pickup on a thin residential kit, and the honest fix is stripping and recoating with a proper two-part system.
Grit, salt and tires wearing the topcoat through its gloss; the coating is intact but tired.
A coating that is chipping, lifting or bubbling anywhere is not recoated; the loose material has to come off first, and if it is loose everywhere the whole coating does.
The coating never bonded: moisture vapor from the slab pushed it off, the slab was troweled too smooth or sealed and never ground, or a one-part "epoxy paint" was used over a floor that needed a two-part system. The diagnosis, on Why Floors Fail →
This is the one item on the page that is never a repair. A peeling coating patched with more coating peels again around the patch.
Cosmetically, yes: the crack is opened slightly, cleaned, and filled with a flexible polyurethane filler if it may move or a rigid epoxy if it is stable, then shaved flush and, on a polished floor, re-polished. What a filler cannot do is stop a crack that is growing or offset, which is the slab moving and a structural question before a flooring one.
It never bonded. Either moisture vapor from the slab pushed it off — the most common reason, and the reason the slab should be tested before coating — or the concrete was too smooth or sealed and was never ground, or a one-part epoxy paint was used where a two-part system was needed. Peeling is not repaired; the coating is stripped, the slab tested and ground, and a proper system applied.
Yes, and it is the maintenance a coated floor eventually needs: degrease, abrade the whole surface until dull, vacuum, and roll on a compatible topcoat. It only works over a coating that is sound and bonded everywhere. Anything chipping or lifting has to come off first, and worn-through spots need a primer.
Hot-tire pickup — the coating lifting where the tires sit — is a thin or one-part residential coating softening under heat. The lifted areas are stripped and the floor recoated with a two-part epoxy and a urethane topcoat rated for it. The prevention is that system in the first place, and a mat under the parking spot in winter for the salt.
A web of fine surface cracks — crazing — is shrinkage in the top skin from when the slab was poured. It does not grow, leak or weaken anything, and it is filled visually by the densifier and sealer used in polishing. A single crack wider than a card, or one that is growing, is a different thing and is worth watching.
Filling a crack is $20 to $60 in materials. An epoxy chip repair kit is $30 to $60. A topcoat over a sound coating runs $1 to $3 per square foot as a kit or $3 to $7 professionally. Stripping a failed coating, preparing the slab and recoating is $3 to $8 per square foot, which is roughly what the floor cost the first time, because it is being done properly the second.