How do you paint a weatherboard house so it lasts?

Check the boards first: paint won't fix rot or a leak

Start with the timber, because new paint over wet or rotten weatherboards won't last. The Queensland Government's heritage note on timber repairs says to check exterior paint for splitting or cracking that may mean water is getting into the timber underneath. It also says repeated wetting and drying is harmful to timber and speeds up decay. So the first job is a slow walk around the house.

• Cracked or split paint. The Queensland note flags it as a sign water may be getting behind the paint.
• Corners and joints. Decay is common in joints that hold moisture, the same note says, including where fascias meet at corners.
• Gaps and worn caulk. Dulux lists moisture seeping through uncaulked joints or worn caulk among the causes of peeling.
• Peeling, blistering or flaking. Dulux's trade advice says paint that's blistering, cracking, flaking or peeling should be completely removed.
• Grey, weathered timber. Dulux lists weathered timber as an unsound surface, and its prep steps say to sand the grey off.

Rotten sections get cut out and patched before anyone paints. The heritage note says patches should be the same species as the existing timber, well seasoned so they don't shrink, with the grain running the same way. It also says to find and fix whatever caused the damage before the repair, so the new timber doesn't go the same way.

If walls, stumps or framing look out of line, the heritage note says to get a structural engineer's advice before any repairs. That's not a painting job. Paint comes after it's fixed.

Got an old hardwood house with VJ walls and verandahs? Our guide to repainting a Queenslander covers the extra detail work.

Prep in order: wash, test, scrape, sand, fill

Good weatherboard prep runs in a set order. This one is drawn from Dulux's Weathershield instructions, Taubmans' exterior guide and the Queensland Government's heritage painting notes.

1. Wash it down. Taubmans says to wash the walls with soapy water, rinse with clean water and let them dry. Treat any mould with a diluted bleach solution and rinse it off well before you paint.
2. Tape test the old paint. Dulux says to cut an X with a sharp knife, press 10cm of tape firmly across it and pull it off fast. If paint comes away, the loose paint has to come off. Test a few spots around the house.
3. Scrape off loose and flaking paint. Get everything that's lifting, right back to paint that's firmly stuck.
4. Sand. Dulux says to sand to a flat finish, remove greyed timber, then dust off. Paint on older homes can contain lead, so get it tested before you sand, since the Queensland Government says homes built before 1970 have probably had lead-based paint used on them.
5. Dull any gloss. Dulux's trade advice says glossy surfaces should be lightly sanded so the next coat has something to grip.
6. Fill. Fill cracks and holes with an exterior filler. On bare timber, Dulux says to use a flexible, exterior grade wood filler for nail holes.
7. Check the weather. Dulux says it has to stay above 5°C while the paint goes on and dries. Rain or overnight dew on wet paint can damage it. In the heat of the day, paint the shady side of the house.

Give the eaves a proper scrub. The Queensland painting maintenance note says peeling between coats often shows up on eaves, because rain doesn't rinse them. Salt from the air builds up there, and new paint won't stick if it isn't cleaned off. Worth remembering on a street near the beach.

Prime bare timber, yes. Sound painted boards often don't need it

Bare timber gets a primer. Sound, clean paint usually doesn't. Dulux calls Weathershield self-priming on most surfaces, and Taubmans calls All Weather a self-priming exterior paint that suits weatherboards. Dulux's peeling fix still says to prime bare timber, and its repair steps say to prime bare spots before you repaint.

The timber type changes the primer. Dulux lists meranti, merbau, jarrah, spotted gum, blackbutt and ironbark as Australian timbers that can hold tannin. Dulux describes tannin staining as brown or tan marks that come from the timber, up through the paint. Here's what Dulux says for each kind of board.

Two timing rules from Dulux's 1Step Prep page. Outside, the topcoat should go on within a week of the primer. And spraying isn't recommended for priming timber, so brush or roll it on.

Old oil paint needs care. The Queensland maintenance note says that, as a rule, oil-based paint goes over an old oil-based system and water-based paint over water-based. If you're putting water-based paint over several layers of old oil paint, it says to put an oil primer on first. Not sure what's on your boards? Find out before you buy paint.

Two topcoats of water-based exterior paint, painted from the top down

Weatherboards get two topcoats over the prep. Dulux says two coats of Weathershield Low Sheen on a clean, sound, prepared surface. Dulux's trade advice adds that the Australian Standard, AS/NZS 2311, generally calls for one prep coat and two topcoats on broad walls. For peeling timber, Dulux recommends repainting with a top quality water-based exterior paint, for adhesion and water resistance.

Sheen is about where the paint goes. Dulux pitches Low Sheen at large exterior surfaces like walls and weatherboards, semi gloss at exterior trims and detailed surfaces, and gloss at smooth doors, window frames and trims.

1. Start at the top. Taubmans says to begin with gutters, then fascias and eaves.
2. Do the boards next. Taubmans suggests a small roller, brush or spray gun for weatherboards. Work in sections and keep a wet edge so you don't get lap marks.
3. Leave trims and window frames till last. Taubmans says to keep windows open while you paint them so they don't stick shut.
4. Wait between coats. Dulux gives Weathershield Low Sheen a 2 hour recoat at 25 degrees and 50% humidity. Taubmans says All Weather can be recoated in 2 hours.

Dark colours work harder on weatherboards. Dulux's trade advice says deep colours soak up more heat, so the surface moves more as it heats and cools. It says deep colours break down sooner than lighter ones in the same spot, and dark paint over old exterior paint can push moisture out and cause blisters. Our instant estimate adds to the price for dark colours that need extra coats. For help picking a shade, see choosing exterior house colours. For the whole-house order, from roof line to downpipes, read how to paint a house exterior.

Timber or fibre cement weatherboards: the prep starts in a different place

Weatherboards come in timber and fibre cement, and the prep isn't the same. James Hardie describes its Linea Weatherboard as a pre-primed, 16mm thick fibre cement board. It says the boards resist shrinking, swelling and warping, which can help the paint finish last longer.

Timber boards need the full timber steps above: sand off greyed timber, fill nail holes with a flexible filler, prime bare hardwood and watch for tannin. If yours are fibre cement, read why Hardie cladding joins fail first before you paint. Not sure which you've got? A painter can tell you at the site visit.

Ladders and second storeys: that part's a job for a painter

Upper walls on a two-storey weatherboard house are a job for a professional painter, not a weekend on a ladder. The Queensland Government says over 1,000 Queenslanders are hospitalised each year after falling off ladders, and most of those injuries happen around the home. It also says never use a ladder in thunderstorms, rain or wind.

Safe Work Australia says construction work with a risk of falling more than 2 metres is high risk construction work. It lists barriers and scaffolding among the ways to stop falls. Second-storey boards, gable ends and high eaves sit well above that line.

Licensing matters too. The QBCC says you need a licence to contract for building work in Queensland valued over $3,300. Ours is QBCC licence 1281728.

If the job needs a ladder above ground floor height, stop the DIY there. Do the ground-floor prep if you like, and get a painter for the rest.

Upkeep: wash weatherboards every 6 months near the coast

Washing is the easy part of looking after painted weatherboards. Dulux recommends washing Weathershield every 6 months in coastal areas and every year in sheltered or inland areas. For regular washing, Dulux says use low pressure water to shift dirt and dust.

Then keep an eye out. The Queensland maintenance note describes crazing as fine, jagged breaks in the top layer of paint, and says it usually shows up on timber. Its fix is hand scraping or sanding, then a repaint. The note also says repainting should ideally happen before the paint fails and the timber starts to go, and that it's especially important for timber.

Don't repaint just because it's been a while, though. The same note warns that repainting sound paint over and over can build up layers that are more likely to peel. For small damage, Dulux says remove the loose coating, prime bare spots, reapply, then put a final coat over the whole panel. For how long a full repaint should last, see how long exterior paint lasts. If it's already flaking, start with why exterior paint peels.

What a weatherboard repaint costs on the Sunshine Coast

A standard repaint of a weatherboard home starts at $10,000 to $25,000 in our instant estimate. Storeys and condition move it from there. These are the estimate's guide ranges for the standard tier, including GST and rounded to the nearest $100.

Weatherboard sits at the top of our estimate's wall types. Exterior house painting cost shows how it compares with render and cladding. We work from Caloundra to Noosa, right across the Sunshine Coast, including exterior house painters in Maleny. The firm price comes after a free site visit with our exterior house painters.