Most weatherboard advice is about the method: what to use, how much pressure, which product. The bigger question is where the board is likely to give you trouble.

Timber weatherboards are built to shed water. Cleaning them badly means working against the one thing they’re designed to do. And Tauranga’s coastal air adds salt to a job that’s already harder here than it is inland.

Here’s where the boards fail, and what that means for cleaning them.

Coastal Tauranga is a different maintenance category

If your house is near the coast, it isn’t on the same cleaning schedule as a house ten kilometres inland.

BRANZ recommends timber cladding be washed down every six months in a coastal environment, and annually once you’re further away from the coast. That’s a maintenance figure from New Zealand’s building research body, not a sales pitch.

The reason is salt. Wind carries it off the sea and it settles on your boards, and salt crystals draw and hold moisture. A coastal wall keeps a damp film on it that an inland wall doesn’t, which means the paint is under more pressure here for the same weather.

Salt also doesn’t just sit on the surface. Painted surfaces near the coast can end up with salt worked into the coating, which is why repainting jobs near the sea often need careful washing before and between coats. A quick rinse doesn’t take it out.

Distance makes a difference. Exposure drops off quickly with distance and shelter, so a house a few streets back is a genuinely easier site than one on the front.

On the coast, your boards aren’t only weathering. They’re living in salt.

Where a weatherboard actually fails

The instinct is that a big flat painted board is the vulnerable part. It isn’t. Almost every weatherboard failure starts at a join or an end.

Take the lap first. Weatherboards overlap, with the board above sitting over the one below, so water runs down the face and off the bottom edge. The lap isn’t a weak point by accident. It’s a designed escape route for water moving downward.

Then the ends. Wherever a board has been cut — at corners, around windows and doors, at any penetration — the end grain is exposed. End grain wicks water into the board the way a straw does, which is why cut ends are primed during construction and why deterioration so often starts at butt ends and corners.

The bottom edges of the lowest boards are the third place to watch. BRANZ names paint failure as the most common cause of timber deterioration, because it lets the timber get wet and stay wet. Paint cracking often shows up at the laps, where the paint film takes the board’s movement first.

Look where the boards meet, and where they end.

Why water blasting is the wrong tool on timber boards

BRANZ is direct about this. Avoid high-pressure water such as a water blaster on timber cladding, because it can erode the paint surface and drive water between the laps and behind the facings.

That second half is the bit worth understanding.

Rain hits a weatherboard and runs down the face, off the bottom edge, onto the board below, and eventually away. A water blaster doesn’t do that. It hits the wall hard enough to push water sideways and upward, straight into the lap joint — the one direction the board was built to keep water out of.

So the problem isn’t only how hard you blast. It’s that any pressure puts water into a gap that exists by design. Turning the machine down reduces the damage without taking the risk away.

The paint suffers too. Blasting erodes the coating, and the coating is what protects the timber underneath. On a coastal house that matters more, because salt is already working on the paint. Strip it faster and you bring forward the day the timber is exposed.

Aimed at a lap, a water blaster fights the board. The board wins that argument eventually, but not in a way you’ll enjoy.

Cleaning the boards properly

Everything above points the same way: work with the board, not against it.

That means cleaning the face and letting water run down and off, the way rain does. Low pressure, with a cleaning solution doing the work. The solution goes on, stays long enough to break the growth down, then gets rinsed away. It lifts the growth; the water only carries it off.

Rinse from the top down, so what comes off the upper boards doesn’t land on the ones you’ve just done. Never angle a nozzle up under a lap.

Then do the corners and cut ends deliberately, because a general wash passes over them. That’s around windows and doors, external corners, and the bottom edge of the lowest boards. They’re also the places that fail first, which is not a coincidence.

The boards then need to dry, and coastal humidity means that takes longer here than the forecast suggests.

On a painted timber house, the coating is what you’re protecting. A clean that removes the growth without eroding paint has done its job; one that takes paint off has cost more than it saved.

The growth sits on the surface. The damage happens at the joints.

The clean is your inspection

BRANZ notes that washing the exterior provides a good opportunity to carry out an inspection. With the growth off and the boards wet, faults that were hidden under a layer of green show up clearly. Someone is already at the wall, and the look costs nothing extra.

What to look at, roughly in order of how much it matters. Paint failing in patches, especially at the laps. A chalky residue when you rub a painted surface, which means the coating has broken down. Rust staining around nail heads. Gaps opening at corners and around windows and doors.

Start where the boards end and meet: butt ends, external corners, junctions with windows and doors, and the bottom edge of the lowest boards. Anywhere water runs or splashes.

Early looks small and local. A failing coating is a repaint. Timber that stays wet is a repair. What separates the two is usually how long the problem sat there unlooked at.

If something looks wrong, look rather than poke. A board that moves or sounds hollow wants a professional opinion, not a screwdriver.

The cheapest thing you can do for a weatherboard house is look at it properly every six months.

Cleaning weatherboard houses in Tauranga: quick answers

If you’d rather someone else did the looking, we’ll clean the boards and tell you what we find.