Garage doors, gates and metalwork: getting paint to stay on

A garage door is often the largest single element on a Perth street frontage, and metalwork generally is where repaints fail earliest. The reason is nearly always the same: metal gives paint nothing to hold on to unless you create it.

Why metal is different

Render is porous — paint keys into it mechanically. Timber has grain. Metal is smooth, non-porous and chemically inert, and it moves substantially with temperature.

So adhesion on metal comes from two things only: a **mechanical key** created by abrading the surface, and a **primer** chemically formulated to bond to that metal. Skip either and the film is sitting on the surface rather than attached to it.

The three metals you will meet

**Colorbond and pre-finished steel.** A factory-cured coating. Sound Colorbond needs washing, dulling and an adhesion primer. Chalked Colorbond needs the chalk removed completely first — this is the most common failure.

**Galvanised steel.** Zinc coating over steel. New galvanising is a genuinely difficult substrate: it is smooth, and it can react with some coatings. It needs weathering or an etch primer. Never paint new galvanising with an ordinary primer and expect it to hold.

**Aluminium.** Usually powder-coated. Very smooth, and the powder coat is designed to resist things sticking to it. Needs thorough abrading and a specialist adhesion primer.

Preparation, properly

**1. Wash.** Detergent, then rinse. Remove all chalk, salt, dirt, road film and any oil or grease. On a garage door, exhaust residue is a real contaminant.

**2. Treat rust.** Back to bright metal — wire brush, abrasive disc, or blasting. Then an inhibitive primer straight away, before flash rust forms. On a coastal property expect rust at cut edges, fixings and the bottom rail of a door where water sits.

**3. Abrade the whole surface.** Not just the bad areas. The entire surface needs to be dulled to give the primer a key. On a large panel this is the slow part and it is not optional.

**4. Dust off.** A clean, dry, dust-free surface.

**5. Prime with the correct primer for the metal.** This is where a general-purpose primer fails. Etch primer for bare galvanising, adhesion primer for powder coat and sound Colorbond, inhibitive metal primer over treated rust.

**6. Two topcoats**, allowing proper recoat times.

Sectional and roller doors

**Sectional doors** have panels, hinges and tracks. Paint the panels, keep coating off the hinges and rollers, and do not paint the tracks — a build-up of film there causes binding.

**Roller doors** are the harder case. The curtain rolls up on itself, so the coating has to be flexible enough to survive being wound and unwound and it must not be tacky. Full cure is essential before the door is used — a door rolled up while the coating is still soft will stick to itself and pull off in stripes. Allow considerably longer than touch-dry suggests.

Gates, fences and balustrade

Wrought iron and steel fencing rusts at the joints and the base where it enters the ground or the concrete. Those are the areas that decide the job.

For balustrade near the coast, treat every fixing individually. Stainless fixings in mild steel, or mild steel fixings in an aluminium rail, set up galvanic corrosion that eats the joint from the inside — a good reason to look closely at what has actually failed before assuming it is the coating.

Heat

Dark metalwork in full Perth sun reaches high surface temperatures, and a dark garage door facing west is one of the hottest surfaces on the property. Apply out of direct sun, follow the shade, and expect a shorter service life on dark colours than on light.