The test that decides it
We cut a small X through the existing coating with a utility knife, apply a strip of high-tack tape, and pull. If the coating stays on the slab, the bond is doing its job. If it comes away in flakes or sheets, the existing floor has already released and anything applied over it inherits that failure. On larger commercial floors we go further and do a pull-off adhesion test with a dolly and a gauge, which gives a number rather than an impression.
Compatibility is the second question
Not every resin bonds to every other resin. A polyaspartic over a well-abraded epoxy is routine. A new system over an unknown coating, particularly a single-part product or something with a wax or silicone in it, may not bond at all, and may look fine until the first thermal cycle. Where the existing product is unknown we do a test patch in a corner and leave it for a few days before committing the room.
What abrading actually means
Not sanding by hand. The existing surface is mechanically abraded with a planetary grinder using a diamond or a sanding attachment, taking the gloss off completely and leaving a uniform matte profile across the whole floor. Any missed area is a guaranteed release point. This is faster and cheaper than full removal but it is not a quick scuff, and a quote that describes a rinse and a recoat is describing a floor that will peel.
When we say take it off
Any visible delamination, blistering, or peeling anywhere on the floor means the whole coating comes off, not just the failed area. Failure that is visible in one place is usually present and not yet visible elsewhere, and there is no way to recoat around it honestly. This is often not what a client hopes to hear, and it is a great deal cheaper than doing the job twice.
Want this answered for your slab?
Free site visit with a moisture reading, then a written fixed price. Across the BC Interior.