Which paint sticks to galvanised metal?
Which paint sticks to galvanised metal?
A mordant wash, a self-etch primer or a purpose-made acrylic primer for galvanising — ordinary oil-based primer peels off in sheets.
The failure everyone meets here is chemical. Zinc reacts with the drying oils in alkyd paint in a saponification reaction, producing zinc soaps at the interface — so the paint film sits on a layer of soap and peels off in large, clean sheets, often a year later and often taking a perfect impression of the surface with it. New galvanising makes it worse, because it carries passivation treatment and processing oils that repel coatings. The answers are to etch the zinc so there is something to key to, or to use a binder that does not saponify, which is what waterborne acrylics offer. Whatever the route, degreasing with a detergent wash comes first, because none of it works over oil.
The options, ranked
| Option | Good at | Bad at |
|---|---|---|
| Mordant solution (T-wash) | Etches the zinc and turns black where it has reacted, so you can see which areas are ready. | Contains phosphoric acid and copper compounds; it needs care, ventilation and proper disposal. |
| Self-etching primer | Acid and binder in one product, convenient in aerosol form for small work. | Thin film, so it needs a proper primer or topcoat over it quickly. |
| Acrylic primer for galvanised steel | Waterborne acrylics adhere to zinc without saponifying, and this is the mainstream modern answer. | Must be a product specified for galvanising; a general acrylic primer is not the same thing. |
| Weathering the surface | Six to twelve months of exposure removes passivation oils and roughens the zinc naturally. | Not an option on a job with a schedule. |
Technique that changes the outcome
- Wash with a detergent or ammoniated cleaner to remove passivation oils, then rinse and dry
- Abrade lightly with a nylon abrasive pad to give a key
- Apply the mordant wash or etch primer and let it react fully — T-wash should turn the surface black
- Prime and topcoat within the primer's stated recoat window
What goes wrong
- Oil-based or alkyd primer directly on zinc
- Painting brand-new galvanising without degreasing and etching
- Sanding aggressively through the zinc layer, which removes the protection you are trying to keep
Compiled practical guidance rather than a published standard. Product formulations vary by brand and market, so read the label — and where the work is structural, electrical or gas, the regulations that apply where you are govern rather than anything here.
Other paint questions
| For | Use |
|---|---|
| Previously painted wood | Clean it, key it and spot-prime bare areas — and find out first whether the existing paint is oil or water based. |
| Bare wood | Knotting solution on the knots, a wood primer, then your topcoat — and prime end grain twice. |
| Plastic | Any paint, provided an adhesion promoter goes on first — and on polypropylene or polyethylene, the promoter is not optional. |
| Kitchens | A scrubbable acrylic eggshell or satin on the walls — and for cabinets, degrease, prime and use a proper cabinet enamel. |
| Bathrooms | A moisture-resistant acrylic in a satin or eggshell sheen with a mould inhibitor — but ventilation, not paint, is the actual fix. |
| Metal | Remove the rust, apply a rust-inhibiting primer the same day, then an alkyd or a direct-to-metal acrylic. |
| Ceilings | A flat matt emulsion — and if there is a water stain or nicotine, seal it with a shellac-based stain block first. |
| Tiles | Tile paint over an epoxy or adhesion primer on a thoroughly degreased and abraded glaze — and expect a limited life in a shower. |
| Fences | A penetrating stain or fence treatment rather than a film-forming paint — and let new pressure-treated timber weather first. |
| Floors | Two-pack epoxy on concrete after a moisture test and a proper grind; floor-grade varnish or floor paint on timber. |
| Radiators | A radiator enamel — water-based acrylic ones no longer yellow, which ordinary gloss on a hot surface always will. |
| Exterior masonry | A breathable mineral or masonry paint — and on an old solid wall, breathability matters more than any durability claim. |
| UPVC | A uPVC-specific paint or an adhesion promoter with an acrylic topcoat — and avoid dark colours, which can distort the frame. |
Common questions
- Which paint sticks to galvanised metal?
- A mordant wash, a self-etch primer or a purpose-made acrylic primer for galvanising — ordinary oil-based primer peels off in sheets.
- What should I avoid?
- Oil-based or alkyd primer directly on zinc Painting brand-new galvanising without degreasing and etching Sanding aggressively through the zinc layer, which removes the protection you are trying to keep
Related pages
- Which paint goes over previously painted wood? Clean it, key it and spot-prime bare areas — and find out first whether the existing paint is oil or water based.
- Which paint should I use on bare wood? Knotting solution on the knots, a wood primer, then your topcoat — and prime end grain twice.
- Which paint sticks to plastic? Any paint, provided an adhesion promoter goes on first — and on polypropylene or polyethylene, the promoter is not optional.
- Which paint should I use in a kitchen? A scrubbable acrylic eggshell or satin on the walls — and for cabinets, degrease, prime and use a proper cabinet enamel.
- Which paint should I use in a bathroom? A moisture-resistant acrylic in a satin or eggshell sheen with a mould inhibitor — but ventilation, not paint, is the actual fix.
- Which paint should I use on metal? Remove the rust, apply a rust-inhibiting primer the same day, then an alkyd or a direct-to-metal acrylic.
- Which paint should I use on a ceiling? A flat matt emulsion — and if there is a water stain or nicotine, seal it with a shellac-based stain block first.
- Which paint can I use on tiles? Tile paint over an epoxy or adhesion primer on a thoroughly degreased and abraded glaze — and expect a limited life in a shower.
- Which paint should I use on a fence? A penetrating stain or fence treatment rather than a film-forming paint — and let new pressure-treated timber weather first.
- Which paint should I use on a floor? Two-pack epoxy on concrete after a moisture test and a proper grind; floor-grade varnish or floor paint on timber.
Sources
- Typical range compiled from manufacturer specifications — At One Place