Why is my garage floor pitting and flaking?
Pitting and flaking are surface failures with different causes, and telling them apart decides whether a coating will hold or simply lift again with the surface underneath it.
- Difficulty
- intermediate
- Time
- 1 hr
- Read
- 2 min
- Safety
- caution
Short answer
Small pits usually mean the surface was weak from the start — over-watered, over-trowelled or dried too fast. Flakes lifting in sheets usually mean freeze-thaw or de-icing salt getting into a porous surface. Either way the loose material has to come off before anything is applied over it.
A garage floor takes a specific combination of abuse: cars bring in water and road salt in winter, the slab is often unheated and close to outdoor temperature, and the surface was frequently finished in a hurry. Surface failure is the usual result, and it is nearly always confined to the top few millimetres rather than being a structural problem.
Safety
Step by step
- Tell pitting from spalling from crazing.Pitting is small holes where the surface has broken out. Spalling is flakes or sheets lifting away, often around a crack or a joint. Crazing is a fine map of shallow cracks with no material loss and is usually cosmetic.
- Look at where it is worst.Concentrated where the car sits, particularly under the wheel arches, points at de-icing salt and water dripping off the vehicle. Spread evenly across the slab points at how the concrete was finished.
- Test how deep the weakness goes.Scrape and tap with a screwdriver. If sound concrete is a few millimetres down, it is a surface failure. If material keeps breaking away, the problem is deeper and worth getting looked at.
- Rule out the structural signs before repairing.Cracks that step, open progressively, or run with a difference in level between the two sides are not surface faults. Those are worth a professional opinion rather than a repair mortar.
- Remove all the loose material.Everything that is drummy, flaking or friable has to come off, back to sound concrete. Anything applied over loose material fails with it, which is why coatings so often lift in sheets.
- Repair with a product intended for thin surface repairs.A polymer-modified repair mortar bonds in thin sections where ordinary sand and cement will not. GuideHQ has a guide on patching a concrete floor for larger holes and broken edges.
- Deal with the water before rebuilding the surface.Salt-laden water dripping off a car is what caused it. A mat under the car, better drainage or simply drying the floor changes the odds far more than the repair product does.
- Consider sealing once repaired.A sealed surface absorbs far less salt and water, which is what drives freeze-thaw damage. That is a separate decision and a separate guide.
Questions people ask
Is a pitted floor dangerous?
Not usually. It is a wear surface problem, not a structural one, unless there are the movement signs described above. It does get worse if left, because each pit holds water.
Can I just coat over it?
Only after removing the loose material. Coating over a friable surface bonds the paint to something that is not attached to the slab, and it lifts — often taking a layer of concrete with it.