Reading a Garage Floor That Has Started to Lift
The Failure Pattern Is the Diagnosis
When a coated garage floor starts coming up, the instinct is to work out what product was used or which contractor to blame. Neither answers the question. The pattern of the lifting does. A coating fails in a small number of recognisable ways, and each one leaves a signature you can read without a lab.
Peeling in Sheets With Clean Grey Concrete Underneath
If you lift a loose edge and it comes away in a continuous sheet, and the concrete revealed beneath it is clean, uniform grey with no coating residue stuck to it, the bond never formed properly. The coating cured into a sound film, it just never gripped. That points at preparation: a slab that was sealed or densified and not opened up, a floor that was acid etched and left with residue, oil or transmission fluid soaked into the concrete before coating, or a surface that was still damp when the primer went down. The coating itself is often perfectly good, which is why it peels as one piece rather than crumbling.
Lifting With Concrete Stuck to the Back
Turn a lifted flake over. If there is a thin grey skin of concrete adhered to the underside, the bond to the coating was fine. What failed was the concrete. Slabs poured with too much water at the surface, or over troweled so that fines and cement paste were drawn up into a weak laitance layer, end up with a top millimetre or two that has very little tensile strength. The coating held onto that layer, and that layer let go of everything below it. This is a substrate problem, and no change of coating product will fix it. The weak layer has to be ground off.
Small Round Blisters
Blisters between roughly 5mm and 40mm across, domed and often clustered, are usually either moisture or air. Moisture blisters come from vapour driving up through the slab and collecting under a film that will not let it through, which happens on slabs with no vapour barrier or where a driveway drains back toward the garage. Air blisters, sometimes called outgassing, form when the slab warms during cure and pushes air out of its own pores into the wet coating. If you slice a blister open and the concrete under it is darker or damp, it is moisture. If it is dry, it is air, and it is a cure day problem rather than an ongoing one.
Tyre Shaped Patches and Edge Lifting
Two roughly rectangular patches where the car sits, matching the tyre footprint, are hot tyre pickup. A hot tyre softens some coatings, especially thin single part products, and lifts them when the car cools and the rubber grips. In Allen, where a car can sit on a slab after a run in genuine summer heat, this shows up more often than people expect. Lifting that starts at the perimeter, the garage door threshold or a doorway is usually a termination detail: the coating was not carried into a saw cut or a chased edge, so water and traffic worked at an exposed film edge until it started to peel back.
Two Checks Worth Doing Yourself
- Tape check: press a strip of duct tape or packing tape firmly onto an intact area, then pull it off sharply at an angle. Coating that comes away with the tape is not bonded.
- Cross hatch: score a small grid through the coating to the concrete with a sharp blade, tape over the grid, pull. If squares lift out cleanly, the bond is marginal across that whole area, not just where you can see damage.
Photograph the Underside
Before you throw away a lifted flake, photograph its back in good light next to a ruler. That single image tells you whether you are looking at a bond failure or a concrete failure, how thick the film was, whether a primer coat is visible as a separate layer, and whether there is contamination on the reverse. It is the most useful piece of evidence in the whole diagnosis, and it is the one most people sweep up and bin before anyone qualified sees it.