Timber window frames demand a different approach to almost every other surface in a Melbourne home. They expand in summer heat, contract in winter cold, and they sit directly in the path of rain, UV and condensation. Paint them without thinking through those conditions and you'll end up with a sash that won't budge, a finish that peels by spring, or moisture locked behind a film that shouldn't be there. This guide covers the full process, from stripping back old paint to the final coat, so the job holds up and the window works the way it should.
Why timber windows are harder than they look
Most homeowners treat a window frame like a wall. It isn't. A wall doesn't move. Timber frames flex constantly as temperature and humidity shift, and that movement is what breaks paint adhesion over time. Older Melbourne homes, particularly those built before 1970, often have double-hung sashes with multiple moving parts, each of which needs to slide cleanly after painting. Apply too thick a coat and the sash binds. Apply the wrong product and moisture gets in through any gap and causes the timber to swell from the inside out.
There's another complication: lead paint. Homes built before 1970 frequently have it on their window frames. If you're sanding back an older frame, test first with a lead paint test kit before generating any dust. Never dry-sand a surface that tests positive.
What to do before you open a tin
Preparation is where window painting is won or lost. Start by checking the condition of the timber. Press a screwdriver gently into any soft-looking sections near the base of the frame and along the sill. Soft, spongy timber means rot, and rot needs to be cut out and filled with a two-part epoxy wood filler before any paint goes on. Skipping this step means you're painting over a structural failure that will keep expanding underneath.
Once the timber is sound, remove the sash from its housing if possible. Painting in place is workable, but pulling the sash out lets you paint all faces evenly, including the edges that contact the frame, which is exactly where moisture ingress and sticking happen most. Use a flat pry bar and work slowly to avoid damaging the parting bead.
Clean the surface with a sugar soap solution and a stiff brush to remove any grease, dust and mould. Rinse and let the timber dry completely. This matters more than most people expect: timber painted while it still holds moisture will blister and peel within a season. In Melbourne's changeable autumn conditions, allow at least 48 hours of dry weather before painting exterior-facing frames.
Sand the existing paint back to a smooth, even surface. You don't need to strip to bare timber unless the existing paint is in poor condition or built up to a point where the sash no longer fits cleanly. Use 80-grit to cut back any ridges or runs, then finish with 120-grit. Pay particular attention to the top and bottom edges of a sash: that's where paint builds up and causes binding.
Primer: the coat that actually does the work
For bare or stripped timber, use an oil-based primer. Oil-based products penetrate the grain far better than water-based alternatives and provide a durable base that resists moisture movement. Dulux Professional Timber Primer is a reliable option for Melbourne conditions. Apply one coat and allow it to cure fully, which typically means a minimum of 16 hours in mild weather.
If the existing paint is in reasonable shape and you're simply refreshing the finish, a bonding primer or a light sanding followed by a direct topcoat is sufficient. The key question is whether the existing paint is still adhering properly. Run a fingernail along the surface: if it flakes or lifts, strip it back rather than painting over it. If you're unsure how the previous coating will perform under a new layer, the same logic applies as when painting over gloss paint, where adhesion is the central challenge rather than colour coverage.
After the primer dries, sand lightly with 180-grit to knock back any raised grain, then wipe down with a tack cloth before applying the topcoat.
Choosing the right topcoat
For exterior timber window frames, a high-quality exterior alkyd enamel or a water-based acrylic enamel with a semi-gloss or gloss finish is the right call. Gloss and semi-gloss sheens resist moisture better than flat or satin finishes and clean up more easily. They also show defects more clearly, which is exactly why the preparation stage matters so much: every scratch and grain ridge reads through a gloss topcoat.
Interior timber frames, particularly in bathrooms or kitchens, need a moisture-resistant product. A semi-gloss acrylic enamel handles condensation well in those environments. The moisture issue in bathrooms is worth taking seriously: if your window frames are in a high-humidity room, the same conditions that damage wall paint also accelerate paint failure on frames. Getting the right product is the first step; the second is making sure the room is properly ventilated so moisture doesn't build up behind the glass.
Apply two topcoats. Let each coat dry until it's firm to the touch before applying the next. Rushing this step is how runs, sags and soft films happen, all of which will show under the finished gloss.
Painting the sash without it sticking shut
This is the step most people get wrong. Paint every face of the sash, including the underside. But leave a deliberate gap on the edges that contact the frame stops. Apply tape to those contact edges before painting and remove it once the topcoat has set but before it cures fully. If the sash is being painted in place, open and close it every 30 minutes for the first 2 hours after the final coat to prevent the surfaces bonding together.
Don't reinstall a sash until the paint has fully hardened. For oil-based products, that means at least 7 days at room temperature. For water-based products, 48 to 72 hours is the minimum. Reinstalling too early is the single most common reason a freshly painted sash sticks.
Cutting in around the glass
Use a narrow cutting-in brush and work at a deliberate pace. You want a thin film of paint to overlap the glass by about 1 millimetre along the rebate: this creates a seal that stops water tracking in behind the frame. More than that and you'll see a visible paint line that catches dirt. Use a painter's tape along the glass edge if your cutting-in isn't confident, but pull the tape while the paint is still slightly wet to avoid lifting the edge when the tape releases.
If you do get paint on the glass, score the dried film with a razor blade at a low angle rather than scraping across the pane. Scraping at the wrong angle scratches the glass surface. Getting this detail right is the same kind of steady-hand work involved in painting around windows generally, where the margin for error is measured in millimetres.
Maintenance after painting
Check the caulking around the frame perimeter once the paint has cured. Caulk shrinks and cracks over time, and a gap at the junction between the frame and the wall is a direct path for water. Use a paintable acrylic caulk, press it in with a wet finger and smooth it flush before painting over it. Re-check this joint every 12 months, particularly after a Melbourne summer.
A well-prepared and properly painted timber window frame should hold its finish for 5 to 8 years in Melbourne's climate before it needs more than a light sand and a fresh topcoat. The frames that fail inside two years almost always share the same history: wet timber, skipped primer, or a sash reinstalled before the paint hardened.