Wash down and check the paint in spring

Wash the outside of the house once a year, in spring, then walk around it slowly in good light. I came to this work as a painter. Paint tells you how the timber under it is doing long before the timber shows it, if you know what to look for.

Paint is the skin

On a timber house, paint is not decoration. It keeps the sun and the rain off the wood. The sun breaks down the binder that holds the paint together, which is why a north or west wall chalks and fades before a shaded one. Salt and grime settle on the surface and attack it. Moss and lichen grow into the paint film, and mould breaks down the resin in it. Once the film cracks, water gets into the timber at the crack and cannot get out. The board swells and shrinks, the paint lifts further, and every season does a little more.

Why spring

Winter leaves salt, grime, mould and moss on the house, most of all on the south side and under the eaves, where the sun never reaches and the rain never rinses. Spring is when the weather starts to dry, the paint has a warm season ahead, and you can see the surface clearly. A clean wall is the only kind you can inspect.

Resene recommends washing exterior paintwork once a year. BRANZ suggests every six months for timber cladding near the coast. Wash the eaves and soffits every time, because salt builds up there first.

How to wash it

• Use a house wash solution from your paint brand, mixed as the label says, and a soft brush or broom. Work from the top down and rinse with plenty of fresh water.
• Do not use a water blaster on weatherboards. The pressure gouges the timber, raises the grain and forces water up behind the boards, and it does not shift chalk properly either.
• Check for mould before you wash. Dab a dark spot with a little household bleach on a cotton bud, then rinse it off. If the mark bleaches out, it is mould, and it needs killing with a moss and mould treatment, not just washing off.
• If the house was painted in the last four weeks, wait. New paint needs that long to cure before it is washed.
• Let the walls dry before you inspect them.

The walk-around

Start on the north and west walls, which take the most sun. Then the south side and anywhere shaded, for mould. Then every sill and bottom edge on the way round.

• Chalking. Rub the paint with a dark cloth or the palm of your hand. A white or coloured powder means the top of the paint film has broken down in the sun. Light chalk washes off and can be left. Heavy chalk, especially with fading, means the paint on that wall is near the end of its life.
• Cracks. Fine lines along the grain or across the joins let water into the wood.
• Lifting and peeling. Look at the bottom edge of the weatherboards, the board ends at corners and scribers, the sills, and the heads of windows and doors. That is where water sits longest and where end grain drinks it in.
• Nail heads. Rust spots, or filler that has dropped out, mean water has a way in at every nail.
• Window putty. On older timber windows, cracked or missing putty lets water in around the glass.
• Soft timber. Press a thumbnail into the bottom of a sill, the end of a board and the foot of a door frame. If it goes in easily, the timber is already wet.

What it tells you

Clean, sound, light chalk. Washed, checked, done for the year.

Chalking and fine cracks on sound timber. Plan a light prep and a fresh topcoat on the worn faces, usually the sunny ones first, over summer. Caught at this stage, it is the smallest paint job there is.

Peeling to bare timber. Book a painter soon. Bare timber goes grey within weeks in the weather, and grey timber has to be sanded back to sound wood before primer will hold. A careful painter primes sanded areas the same day, before the evening dew can get under the edges.

Soft timber. A carpenter before the painter. Paint over rot fails with the rot.

Before anyone sands: lead

If the house was built in the 1980s or earlier, Health New Zealand's advice is to presume there is lead-based paint somewhere in its layers. Test before anyone sands. Test kits are sold in paint and hardware stores. Wet sanding keeps the dust down. Dry sanding needs a proper toxic dust respirator and extraction, flakes are collected rather than washed into the garden, children and pets stay away from the work, and paint debris is never burnt. A painter who works on older houses will raise this before you do. If yours doesn't, ask.

When to call a painter

Paint needs dry timber and the right weather. Resene's guidance is not to coat timber above 17 per cent moisture content, to apply waterborne paint above 10°C, to keep out of direct hot sun, and to finish early enough for the paint to dry before the evening dew. That is why exterior painting belongs in summer, and why the time to book it is spring.

Ask for the preparation written into the quote, line by line. Exterior paint and finishes that last in New Zealand covers what good prep looks like. And ask the painter to write down the brand, the product, the colour name and code, and the sheen, and photograph the lid of the tin. With that on your record in the Archive, next spring's touch-up matches the wall.