Almost every coating failure we are called to has the same cause. Not the wrong product. Not bad luck. The slab was never opened up properly, so the coating never bonded to it.
Because this happens before anything visible goes down, most homeowners have no idea whether it was done. Here is how to know.
What grinding is for
Concrete straight off a power trowel is hard, smooth and closed. There is nothing for a coating to grip.
Diamond grinding cuts that surface away and leaves an open profile: a texture of exposed pores and micro-roughness that the coating flows into and keys against. The bond is mechanical, not chemical.
Get the profile right and the coating is anchored into the concrete. Get it wrong and it is a film sitting on top.
What proper preparation involves
A planetary grinder with diamond tooling. A heavy machine with counter-rotating heads carrying diamond segments. It is loud, it runs for hours on a two-car garage, and it is connected to a vacuum extractor.
Multiple passes in different directions. One pass leaves scoring in one direction. Crossing over gives a consistent profile.
Hand grinding at the edges. A planetary machine cannot reach a wall, a corner, or around a column. Those get done with a hand grinder, and skipping them is why so many floors start lifting at the perimeter.
Removing whatever is on the surface. Old paint, previous coatings, sealers, curing compounds, adhesive. All of it.
Vacuum extraction throughout. Grinding concrete produces silica dust, which is a genuine health hazard as well as a mess. Extraction is not optional.
A final vacuum before coating. Any dust left on the profile sits between the coating and the concrete.
What acid etching does instead
Acid etching means applying an acid solution, letting it react with the surface, then rinsing.
It is fast. It is cheap. It takes twenty minutes instead of several hours. And it is the reason a large share of failed floors in this city failed.
The problems: it opens the surface unevenly, because it reacts with whatever it touches and concrete is not uniform. It leaves residue that has to be neutralised and rinsed thoroughly, and frequently is not. It does not remove existing coatings or contamination at all. And it leaves the slab wet, which then has to dry completely before anything goes on.
Acid etching has legitimate uses in some settings. Preparing a garage slab for a coating system is not one of them.
How to tell during the work
Listen. A planetary grinder is unmistakable and it runs for hours, not minutes. If preparation was finished before mid-morning on a two-car garage, ask what was done.
Look for the vacuum. A grinder without extraction fills the space with silica dust. Its absence tells you about the operation generally.
Check the perimeter. Look at where the floor meets the wall. If it looks the same as it did before while the middle looks freshly cut, the edges were not done.
Look at the slab before coating. Properly ground concrete looks matte, uniform and slightly rough, with the aggregate structure beginning to show. It should not look glossy, and it should not look wet.
How to tell afterwards
If your floor is already down, one honest test: look at any spot where the coating is damaged or has lifted.
If concrete is stuck to the back of the coating, it bonded. That failure was something else, probably impact or moisture.
If the underside is clean and glossy with nothing attached, and the slab beneath looks smooth, the grind was skipped or inadequate.
You can also look at the slab colour where it shows at a threshold. Ground concrete looks different from untouched concrete for a long time.
The profile standard
The trade uses a scale for surface profile, from very smooth up to heavily scarified. Different systems want different profiles: a thin coating wants a lighter profile, a thick trowel-applied system wants an aggressive one.
You do not need to memorise the numbers. What matters is that a contractor knows the profile their system requires and can tell you what they are targeting. One who has never thought about it is following a routine rather than a specification.
Why anyone skips it
Grinding is the hardest, dustiest, slowest part of the job. It consumes diamond tooling, which is a real consumable cost. And it is completely invisible in the finished result.
A crew that etches instead can do two floors in a day rather than one. The customer sees the same floor on completion. The difference shows up eighteen months to three years later, by which time the relationship is long over.
That is the entire economics of the cheap end of this trade.
The one question
If you ask a contractor nothing else, ask how they are preparing the slab.
Diamond grinding or shot blasting: good. Acid etching, chemical prep or pressure washing: that is your explanation for both the low price and the floor you will be replacing.
More on the full process at garage floor coating, and on diagnosing a floor that has already failed at repair and recoating.
Common questions
How long should grinding take on a two-car garage?
Several hours including edge work, not minutes. It is the longest single stage of the day.
Is the dust dangerous?
Silica dust is a genuine respiratory hazard, which is why extraction is used. It is also why the garage needs to be sealed off from the house.
Can shot blasting replace grinding?
On large commercial areas, yes, and it is faster. Edges, corners and around obstructions still need hand grinding either way.
My floor was etched and it looks fine. Is it going to fail?
Probably, though it may take a couple of years. The failure signature is sheets lifting with a clean glossy underside and no concrete attached.
Does new concrete need less grinding?
More, usually. A power-trowelled builder slab is harder and more closed than an old worn floor, and may have curing compound on it as well.
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