Cleaning woodwork before painting

After years of rain, traffic and wind, window frames, doors and fascias often look greyer than you think. On the north side green growth appears on sills and bottom rails, in the city a layer of fine dust and soot settles, and towards the coast salt can be left behind on the woodwork. Indoors, doors and frames pick up grease from hands. Painting straight over that puts new paint on a poor base. In this article you will read why cleaning and degreasing is a standard step when painting woodwork, which approach suits which kind of dirt and what cleaning reveals about the condition of your window frames.

1. Why clean first

Paint does not stick to dirt and grease. Woodwork that is repainted without being cleaned gets a coat of paint that sits on a film of dust, grease and growth rather than on the surface itself. The result looks fine for the first few months but comes away sooner, especially on sills and bottom rails where rainwater runs down. Algae and mould that have not been removed can also grow under or through the new layer.

Cleaning is therefore not a luxury but the first step in exterior painting that lasts. It is part of preparing window frames, windows, doors and fascias, just like sanding, repairing and priming, and it deserves the same attention.

2. Types of dirt

Not all woodwork is dirty in the same way, and the approach depends on what is on it:

• Green growth from algae and moss, especially on north-facing window frames and under trees.
• Fine dust and soot from traffic, typical of window frames on busy streets in Amsterdam.
• Salt deposits from sea air, a point to watch for woodwork towards the coast near Haarlem.
• Grease and grime from hands around handles, door pulls and the opening parts of windows.

Each type calls for its own approach. Algae are treated with a product that actually kills the growth, so it does not return quickly. Soot, fine dust and grease come off with a degreaser suitable for painted timber, after which everything is rinsed thoroughly with clean water.

3. Cleaning and degreasing

Woodwork calls for a gentle approach: a degreaser, a sponge or soft brush and rinsing with clean water. Pressure washing may seem quicker, but it roughens the wood grain, blasts sealant out of the joints and forces water into corner joints and behind glazing beads. That moisture has to come out again later, and as long as it is in there, painting cannot go ahead.

Degreasing comes before sanding, never the other way round: sanding first only rubs the grease into the scratches and into the wood. Fascias and bargeboards high up on the house get the same treatment as the window frames, even though you can see the dirt less clearly from below. If you are planning to give your window frames a different colour at the same time, first read about choosing a window frame colour.

4. What cleaning reveals

Clean woodwork shows its true condition. Hairline cracks in the paint, split sealant joints, flaking patches and wood rot in window frames, sills or fascias become visible as soon as the layer of dirt is gone. That is exactly why cleaning is so valuable: it gives an honest picture of what needs repairing before the paint goes on.

On the exterior woodwork in Amsterdam-Noord, for example, the wood rot was repaired first, after which the wood was given primer and two coats of Sikkens exterior gloss. You can see the result in the exterior woodwork project in Amsterdam-Noord. If it concerns the window frames of an apartment building, the work is usually arranged through the owners' association; see painting for an owners' association.

5. Dry first, then paint

After cleaning, the woodwork has to dry thoroughly. How long that takes depends on the weather, where the timber sits and the amount of water used. Wood that is still damp leads to blistering and adhesion problems in the new paint. So plan cleaning and painting for a period of dry and not too cold weather. Which months are best suited to that is explained in the best season for exterior painting.

During the free consultation our painter assesses how dirty your window frames, doors and fascias are and which cleaning suits them. The quote lists that step separately, so you know exactly what will be done. You can read more about the approach in the city in exterior painting in Amsterdam.

In practice this topic belongs with exterior painting and wood rot and window frame repair. There you can read about the approach and the options, or request a free, no-obligation quote straight away.

Further reading: Window frames: paint or replace?, How to recognise wood rot in window frames, Painting a stairwell: what to look out for.

Frequently asked questions