How to paint exterior wood: windows, shutters and pergolas
To paint exterior wood, choose a dry day without direct sun, clean and sand the wood, treat damaged areas, apply primer and use a finish made for exteriors. Exposed wood takes sun, rain and damp, so preparation and protecting the end grain and joints are what matter most for durability.
Choosing the day and assessing the condition
Avoid painting in rain, in very high humidity or when the wood is still wet. Also avoid strong sun on the surface, because the paint dries too quickly and may blister. A dry morning without strong wind is usually good.
Before starting, examine the wood. Prod suspect areas with a screwdriver. If the wood crumbles or gives way, it is rotten and must be repaired or replaced before painting.
- Peeling paint: scrape back to the firm part.
- Grey, dry wood: sand until you see sound wood.
- Dark, soft wood: probable rot, treat or replace.
- Cracks at the joints: seal with a product made for exteriors after priming.
Cleaning, sanding and repairing
Wash the wood with water and mild detergent, using a brush. If there is mould or algae, apply a product made to treat it and follow the label instructions. Rinse and leave to dry completely, which can take several days in damp weather.
Scrape off loose paint and sand the edges so there are no visible steps. Also sand firm surfaces to remove the shine. Fill small holes with filler made for exteriors.
Tip: Old windows and shutters may have layers of paint containing lead. Before scraping or dry sanding, assess the risk. Protect the floor, avoid spreading dust, wear a suitable mask and keep children away.
Primer and coats
Primer is important on exterior wood. Apply it over the whole surface, including the end grain and corners, which is where water gets in fastest. If the wood has resinous knots, use a product that seals them.
- Apply the primer and leave to dry for the time stated on the tin.
- Sand lightly and remove the dust.
- Apply the first coat of finish, in a thin layer.
- Apply the second coat after the drying time. You may need a third if the colour is very different from the previous one.
Use a product suited to exteriors. There are enamels, woodstains and oils. Enamels cover and form a film. Woodstains let the grain show through and protect, and may be easier to renew.
Specific precautions
On windows, do not paint the hinges, the rubber seals or the hardware. Protect them with tape or remove them. Do not let the paint stick the sash to the frame: open and close the window while the paint has not yet hardened and then check that it does not stick.
On pergolas, start at the top and work down. Paint all faces of the beams, including the undersides, and pay attention to the connection points and the end grain. If the wood is in contact with the ground, protect the base.
On shutters, take them off whenever possible and paint them lying flat, on both sides. If you paint only one side, the wood may warp with the damp.
Plan regular checks. If you see the paint beginning to crack, touch it up early. It is much easier than redoing everything.
Tip: Do not use interior paint outdoors. It cannot withstand sun or rain and will peel faster.