Which paint should I use on a concrete or garage floor?
Why floor paint fails on concrete far more often than on any other substrate, the moisture test that comes first, and how to choose between acrylic, single-pack polyurethane and two-pack epoxy.
- Difficulty
- intermediate
- Time
- 30 min
- Read
- 5 min
- Safety
- caution
Short answer
Test for moisture first by taping a square of polythene down for a day or two — if the underside is wet, no coating will hold. Then match the product to the load: acrylic floor paint for a light-use utility floor, single-pack polyurethane for a garage floor walked on and lightly driven on, two-pack epoxy where tyres stand and things get dragged.
Floor paint peels more than any other domestic coating, and it is almost never the paint's fault. Concrete releases moisture for a long time, holds a weak dusty layer at the surface called laitance, and often carries decades of oil. Any of those three will break the bond, and all three are dealt with before the tin is opened.
Safety
What you'll need
- A sheet of polythene and strong tape, for the moisture test
- A stiff brush or scarifying disc, and a degreaser
- Concrete floor primer or sealer matched to the coating
- A long-pile roller on an extension pole
- A hired floor grinder or diamond cup wheel for a large or contaminated slab
Step by step
- Test the slab for moisture before deciding anything.Tape a piece of polythene about 500mm square tightly to the floor on all four edges and leave it a day or two. Condensation on the underside, or a darkened patch of concrete, means moisture is still coming up. A slab without a functioning damp-proof membrane will lift any coating you put on it, and needs a moisture-tolerant system or a membrane rather than paint.
- Get rid of the laitance and the contamination.New or power-floated concrete has a weak, closed, dusty surface layer. It has to be opened up, either by acid etching with a proprietary etchant or, far better, by mechanical grinding. Old floors need every trace of oil out — degrease repeatedly and let it dry, because oil under a coating guarantees failure.
- Choose the product by the load, not by the room.Acrylic or water-based floor paint: cheap, low odour, easy, fine for a store room or a utility floor with foot traffic. Single-pack polyurethane: tougher, better chemical resistance, the usual sensible garage choice. Two-pack epoxy: by far the toughest and the only realistic answer where car tyres stand and turn, but it has a limited pot life once mixed and is unforgiving of poor preparation.
- Understand hot tyre pickup before you buy.A warm tyre standing on a coating that is not fully cured, or on a coating not rated for it, softens the film and lifts it when the car moves. This is the classic garage floor failure. It is a property of the coating and of full cure time, and it is the main reason epoxy is specified where cars park.
- Prime with the system's own primer.Floor primers are formulated to soak into porous concrete and give the topcoat something to bond to. Use the one from the same range. On a dusty slab, a penetrating sealer or stabiliser is the difference between a coating that lasts and one that comes up with the first dropped tool.
- Apply thin and let it cure fully.Roll it out at the stated spreading rate, cutting the edges in first with a brush. Thick coats stay soft in the middle and never reach full hardness. Then leave it: light foot traffic long before the coating is ready for a vehicle, and full chemical and tyre resistance later still. The tin gives both figures and they are far apart.
- Add grip where it will get wet.A cured floor coating is slippery underfoot when wet. Broadcast an anti-slip aggregate into the wet final coat, or use a coating supplied with one, anywhere a wet car will drip or a door lets rain in.
Tips
- Grinding beats acid etching in every respect except cost — it removes laitance, oil-soaked surface and old coating in one pass and leaves a genuinely keyed surface.
- Two-pack epoxy has a pot life measured in tens of minutes once mixed. Set out everything, plan the route out of the room, and mix only what you can lay before it goes off.
- Interlocking PVC garage floor tiles are the honest alternative on a damp slab: they need no bond to the concrete and can be lifted.
Common mistakes
- Painting a slab that has no damp-proof membrane — Moisture rising through the concrete has nowhere to go once the surface is sealed. The coating blisters and lifts in sheets no matter how well it was applied.
- Skipping degreasing on an old garage floor — Oil that has soaked into concrete migrates back to the surface. A coating over it never bonds and peels in exactly the patches where the car stood.
Alternatives
- Interlocking floor tiles: Laid loose over the slab, so slab moisture is irrelevant. Warmer, quieter and easily lifted or replaced. More expensive per square metre than paint.
- Polished or sealed concrete: Grinding and a penetrating sealer rather than a film coating. Nothing to peel, and it keeps the slab breathable, but the appearance is the concrete you already have.
- Resin screed: A trowel-applied system several millimetres thick, laid by a contractor. Expensive, and the right answer where the slab surface itself is broken up.
Questions people ask
Why does my garage floor paint keep peeling where the car parks?
Hot tyre pickup, oil contamination, or moisture from below — usually a combination. A warm tyre bonds to a soft or under-cured film and lifts it when the wheel turns.
How long before I can park on a newly painted floor?
Far longer than it takes to walk on. The tin will give a separate figure for full cure and vehicle traffic — it is commonly several days to a week, and driving on it early is the most common way people ruin a good job.
Can I paint over old flaking floor paint?
No. Anything loose has to come off, and the honest answer on a badly failed floor is usually to grind the lot back and start from the concrete.