Why is the paint peeling off my radiator?
Radiator paint fails for three reasons — heat, poor preparation, or the wrong paint — and heat is the one people forget when they use ordinary emulsion or gloss.
- Difficulty
- beginner
- Time
- 1 hr
- Read
- 2 min
- Safety
- caution
Short answer
Ordinary paint is not formulated for a surface that cycles between room temperature and hot, repeatedly, for years. Add the fact that radiators are rarely keyed properly and often have residual dust and grease on them, and the film lets go. Strip back to sound material, degrease, key thoroughly and use a paint rated for radiators.
A radiator is a worse surface to paint than it looks. It is smooth and often already coated, it expands and contracts every time the heating comes on, it collects a fine film of household grease, and the back and the top are almost impossible to prepare. Most peeling is preparation rather than product, but product matters too.
Safety
Step by step
- Turn the heating off and let it go completely cold.Painting or preparing a warm radiator flashes off the solvent or water far too fast, which is itself a cause of poor adhesion, and it is unpleasant to work on.
- Remove the loose paint back to a firm edge.Scrape until nothing more lifts. As with any peeling paint, whatever you leave that is loose will take your new coat with it.
- Degrease the whole radiator properly.This is the step that is nearly always skipped. Radiators sit in kitchens and living rooms and collect an invisible film. Wash with a suitable degreaser, rinse, and let it dry fully.
- Key every surface you can reach.Abrade to a uniform dull finish. The existing coating on a radiator is usually a hard factory finish with no key at all, and paint will not stick to it as it is.
- Treat any rust before painting over it.Bare or rusted metal needs the rust removing and an appropriate metal primer. Painting over rust traps it and the paint lifts as it continues underneath.
- Use a paint intended for radiators.These are formulated to stay flexible and stable through heat cycling and to resist yellowing. Ordinary gloss on a radiator commonly yellows badly as well as failing.
- Apply thin coats and let each cure fully.Thick coats on a surface that expands and contracts crack sooner. Follow the recoat times and, importantly, leave it as long as the tin says before putting the heating on.
- Leave the valves and the head alone.Paint on a thermostatic head can stop it sensing correctly, and paint in a union nut makes any future plumbing work harder. Mask them.
Common mistakes
- Painting a radiator with ordinary white gloss. — It yellows quickly under heat and is not formulated for repeated thermal cycling, so it embrittles and cracks.
- Turning the heating on before the paint has cured. — Heat on an uncured film causes blistering and a soft finish that marks permanently.
- Skipping the degrease because the radiator looks clean. — The film that causes adhesion failure is invisible. Looking clean is not evidence of being clean.
Questions people ask
Does painting a radiator reduce its output?
A normal thickness of paint has a very small effect. Many coats built up over decades, or thick textured finishes, matter more. Metallic finishes have historically been claimed to reduce radiant output somewhat.
Can I paint the back and the wall behind?
Only if the radiator can be taken off its brackets safely, which is a plumbing job. Otherwise paint what you can reach and accept the rest.