How to paint metal window frames

Inspired by a helpful YouTube guide. We based this walk-through on the video "DIY CRITTALL WINDOWS on a budget VLOG", which covers the preparation and painting process for steel-framed windows in a UK home setting. Crittall is a well-known UK steel window manufacturer, and the process shown applies broadly to similar steel and metal frames. The masking approach and paint application sections are particularly useful. Worth a watch before you start.

1. Clean the frames thoroughly

Before anything else, remove dirt, mould, and grease from the frames. Paint will not stick to a dirty surface. Use a stiff brush to get into the corners, then wash down with a sugar-soap solution and rinse with clean water.

Pay attention to any mould - black or green patches on metal are usually surface-level but worth treating with a dilute bleach solution before painting. Rinse thoroughly and let the frames dry completely before moving on.

2. Sand back to sound paint or strip to bare metal

Where the existing paint is sound and well adhered, a light sand with 120 grit is enough to key the surface. Where paint is flaking, blistering, or bubbling, you need to take it back further - down to where the paint is solid, or right back to bare metal if there is significant rust beneath.

Use wet-and-dry paper for detail work around glazing bars and in corners. A wire brush attachment on a drill speeds things up on flat sections. Always wear eye protection when working on old paint - pre-1960s frames may contain lead paint, so check before sanding and wear a proper mask if in doubt.

3. Treat rust with rust converter

Steel frames rust. Any bare metal showing rust needs treating before you prime, otherwise the rust continues under the new paint and lifts it within a couple of seasons.

Apply a rust converter directly to the affected areas with a small brush. The converter chemically reacts with the rust and turns it into a stable black compound that can be painted over. Let it cure fully - usually at least four hours - before priming. This step applies to steel only; aluminium does not rust.

4. Apply metal primer

Primer is not optional. On steel frames, use a metal primer after the rust converter. On aluminium or galvanised frames, use an etch primer, which bites into the surface chemically and gives topcoats something to grip.

Apply a thin, even coat with a good-quality brush. Work methodically from top to bottom. One coat of primer is usually enough, but if you see any missed patches or thin spots once it is dry, go over them before moving on to the topcoat.

5. Mask the glass carefully

Good masking saves a lot of time cleaning up later. Use low-tack masking tape and press the edge down firmly with a fingernail to stop paint bleeding underneath. On older windows with slightly wavy or uneven glazing bars, this takes some patience.

The tape should sit about 1mm inside the frame edge - that 1mm of glass that paint slightly covers actually helps seal the frame-to-glass joint against moisture. You will cut the line crisp at the end anyway.

6. Apply two coats of metal gloss or satin

Use a specialist metal paint - something like Rust-Oleum, Hammerite, or a thinned metal gloss. Thin the first coat by 10–15% with the appropriate solvent; this helps it penetrate any remaining surface texture and gives a better bond. The second coat goes on full strength once the first is dry.

Work in good light so you can see runs and misses as you go. Thin coats with a lightly loaded brush beat thick ones every time for metal windows. Thick coats sag and take an age to dry.

7. Cut in neatly at the glass

Even with masking tape, the final neat line at the glass takes a bit of care. Use a fine-tipped cutting-in brush or a window scraper held at an angle to cut through any slight bleed once the paint is dry.

Some painters prefer to mask lightly and then cut the line freehand with a steady-handed brush - it is quicker on lots of small panes. It depends on your confidence and the complexity of the window. Either way, the aim is a consistent 1–2mm overlap onto the glass.

8. Remove masking tape while the final coat is still slightly tacky

Pull the tape off while the topcoat is still slightly soft - not wet, but not fully hard either. This stops the paint film cracking along the tape edge, which can happen if you wait until it is bone dry before peeling.

Pull the tape back at a low angle, slowly and steadily. If any paint lifts, press it back gently and let it cure. Once fully dry, check over the whole frame and touch in any small gaps or edges that need it.

When to call a handyman

Painting metal window frames is fiddly, especially on older properties with lots of small panes. If you have a whole houseful of steel-framed windows or the frames need repair work before painting, it is worth getting a professional in. Richard can help with painting and minor repairs across Sandwich, Deal, and nearby East Kent.