Surface prep
Why garage floor
coatings peel.
Almost nobody’s coating failed because they picked the wrong brand. It failed at the bond line — the place where the coating meets the concrete. Here’s what actually goes wrong.
Peel a failed garage floor coating up and look at the back of it. That tells you more than any product label. If there’s concrete stuck to the underside, the coating held and the slab gave way. If the back is clean and shiny, it never really bonded at all — and that is the far more common story.
1. Something was between the coating and the concrete
Oil, transmission fluid, tire shine, silicone, driveway sealer, curing compound left over from when the slab was poured. Concrete is porous, so these things don’t sit on top waiting to be mopped off — they soak in and stay there.
A clean-looking floor can still contain contamination. Cleaning and mechanical preparation must follow the selected system’s requirements. Diamond grinding or shot blasting can remove unsuitable surface material, but deeply absorbed oil may need further treatment or removal of affected concrete. No machine pass guarantees that contaminated concrete is ready to coat.
2. The top of the slab was weak
The very top of a concrete slab isn’t always the strongest part of it. Over-troweled floors develop a dense, slick skin. Slabs finished with too much water on the surface get laitance — a soft, dusty layer of fines and cement paste sitting on good concrete underneath.
You can bond a coating perfectly to that layer and still fail, because the layer itself peels away from the slab. The coating did its job. The surface it was stuck to didn’t.
This is the failure mode that surprises people most: the coating comes up in sheets with a thin crust of concrete on the back, and everyone blames the product.
3. Moisture pushing up from underneath
Moisture within or moving through a slab can contribute to blistering and adhesion failure when conditions exceed the selected system’s limits. Testing and investigation matter; the appearance of a failed coating alone does not establish the cause.
Irrigation, drainage, a missing vapor barrier under the slab, or just a wet winter all change the numbers. A moisture reading tells you what the slab is doing that week, not forever — which is exactly why it’s worth taking before you commit, and why a coating chosen for a dry slab can fail on a damp one.
More on how moisture testing actually works →
4. The prep didn’t match the system
Every coating system specifies a surface profile — how rough the concrete needs to be for that particular product to key into it. Thin coatings want a light profile. Thick, high-build systems want an aggressive one.
Acid etching produces a very light profile at best, and on a hard-troweled floor it often produces almost nothing. It also leaves residue that has to be neutralized and rinsed, and if that rinse isn’t thorough you’ve added a contaminant while trying to remove one.
Diamond grinding or shot blasting?
Diamond grinding uses abrasive tooling; shot blasting propels and recovers steel shot to prepare the concrete. Either may be specified to achieve the required ICRI concrete surface profile (CSP). Selection depends on the coating, concrete condition, removal requirements and access. They are alternatives, not two steps every floor automatically needs.
If you have heard “bead blasting,” ask which media and method are actually proposed. For this kind of concrete preparation, steel shot blasting is the more precise term; glass bead blasting is not an interchangeable specification. The required profile and cleanliness still have to be achieved. See Sika’s mechanical preparation guidance.
5. It was installed outside the window
Resinous coatings are chemistry on a timer. Mix ratio, material temperature, slab temperature, humidity, pot life, and the gap between coats all have limits, and in the Inland Empire the temperature swing between a July afternoon and an October morning is enough to change all of them.
Too hot and the base coat kicks before the flake is broadcast, so the chips sit on top instead of embedding. Too cold and it never fully cures. Miss the recoat window and the layers stack rather than bond to each other, which is how you get a floor that delaminates internally — the base is fine, the topcoat sheets off it.
The short version
If you’re getting quotes, the useful questions aren’t about brands. They’re these:
- Which prep method and profile are specified? Ask whether diamond grinding, shot blasting or another approved method will achieve the system’s required CSP.
- Will you moisture test? And what happens to the price if it reads high.
- What happens to the cracks? Filled and ground flush, or coated over.
- What’s the recoat window and what if the weather turns? A real answer means they’ve thought about it.
A coating that’s bonded to sound, clean, properly profiled concrete is remarkably hard to kill. Nearly everything else is a shortcut somewhere in the first two hours of the job.
