Plaster homes are usually described as low maintenance. New Zealand’s building guidance says something different: these exteriors generally need more looking after than a weatherboard house.

The reason comes down to how each one keeps water out. Weatherboards overlap and drain. A plaster wall has no laps and no drainage path across its face, so the coating is what does the work.

That changes what cleaning is. Here’s what it involves, and what isn’t a cleaner’s call.

The cladding sold as low maintenance needs more of it

MBIE’s building maintenance guidance is direct about this. Homes with monolithic claddings are often sold as low maintenance, but those exteriors generally need more looking after than a weatherboard house.

The reason is structural. Weatherboards overlap, each board sitting over the one below, so water runs down the face and off the bottom edge. The geometry does the work, and a scratched board is a paint problem.

Plaster has none of that. A monolithic wall is one sealed surface, no laps, no drainage path across its face. It keeps water out with its coating.

So the paint isn’t a finish sitting on top of the cladding. It is the waterproofing. A crack, a scraped patch, a seal that has failed at a window — on a weatherboard house those are cosmetic. On a plaster wall, each one is a route into the wall.

Cleaning follows. You’re maintaining the layer that protects the house, removing growth and salt that hold moisture against the coating.

Which is why the answer on method isn’t “use less pressure”. It’s don’t put pressurised water against a sealed skin — the difference between the two approaches is set out here.

On a plaster house, a chip in the paint is a hole in the roof.

Why this matters more in Tauranga than in most places

Plaster and monolithic cladding became common in New Zealand through the 1990s and early 2000s, and a lot of it went up here.

That period had a known problem. These systems were often fixed directly to the framing, with no gap behind them for water to drain or dry. Water that gets behind a sealed skin with nowhere to go sits against the framing. That combination is what caused the weathertightness failures of that era, not the plaster itself.

Since 2004, the same systems have been installed over a drained and ventilated cavity on treated framing. A plaster home built that way is as weathertight as any other modern cladding, and that covers most plaster homes built since.

So where does that leave Tauranga? The region built heavily during the earlier window, and it has sat among the districts with the highest number of weathertightness claims.

None of that says anything about your house. What it does say is that on a plaster home, the coating is the maintenance worth keeping up. It’s the part still doing work.

What coastal salt and humidity do to that coating

Tauranga’s humidity keeps exterior surfaces damp for longer than the forecast suggests, and why that happens is covered here. On plaster, the salt is what behaves differently.

Wind carries salt off the sea and it settles on the coating. Salt crystals draw and hold moisture, so a coastal wall keeps a damp film on it that an inland wall doesn’t. On a weatherboard house that film sits on boards that drain. On a plaster house it sits on the layer doing the waterproofing.

And salt doesn’t stay on the surface. Coastal surfaces can end up with salt worked into the coating itself, which is why repainting jobs near the sea need careful washing between coats. A quick rinse doesn’t remove it.

Both salt and constant damp break a coating down faster, and a coating that’s breaking down is a sealed skin starting to let water through.

MBIE’s guidance flags coastal walls, with a detail worth knowing. Wash cladding where the house is near the sea, and on wall areas sheltered from regular rain washing. The walls the rain never reaches are the ones that need cleaning most.

On the coast, a plaster house is only as watertight as its paint.

Cleaning it without breaching the surface

MBIE is specific here. Use a soft brush and a low-pressure hose, and do not use a water blaster, which can damage claddings and force water through gaps and joints.

That’s worth understanding rather than just following.

A water blaster does two things to a plaster wall. It breaches the coating, and it drives water into the joints the coating exists to seal. A weatherboard can still drain after water gets under a lap. Plaster has nothing behind it to drain into.

The job itself is simple. Low pressure, with a cleaning solution doing the work rather than the water — applied, left long enough to break the growth down, then rinsed away. Work from the top down.

Keep water off the junctions. Windows, doors, corners and anything fixed through the cladding are where the coating is interrupted, and a soft brush covers those better than a hose. Growth and salt sitting in a corner or along a joint come off with low pressure — exactly where pressure would put water in.

The surface is the waterproofing, so clean it the way you’d clean anything you don’t want to puncture.

What to look at, and what isn’t ours to judge

A wash is the best look your cladding gets all year. MBIE says to inspect it at least annually, and with the growth off and the surface wet, the coating’s condition is easy to read. You’re already at the wall.

What MBIE says to check: water can get in through holes, cracks, loose cladding, around fixings like aerials, through separated joints, around doors and windows, and anywhere sealing has failed or water can pool. Their guide to the signs of a leaky home covers it in full.

Two distances worth measuring. Cladding should sit at least 175mm above lawn or garden, and 100mm above paving. If soil or paving has crept up, water reaches the bottom of the wall every time it rains.

On the coating itself, watch for growth or salt left sitting against it, and sealant at junctions that’s cracked or gone.

Then the boundary. Coating condition is what a house washing deal is, and where the coating needs more than cleaning, prep work before repainting is the next step. Whether water has already got behind the cladding is a weathertightness question, and MBIE is clear that this work needs a licensed building practitioner. Not a cleaner, and not a blog post.

We can tell you what the coating looks like. What’s behind it needs someone qualified.

Cleaning plaster houses in Tauranga: quick answers

Can I water blast a plaster house?
No. MBIE’s guidance for these claddings is a soft brush and a low-pressure hose, and it says so because a water blaster can damage claddings and force water through gaps and joints.

Why is plaster different from weatherboard?
Weatherboards overlap, so water that gets behind the paint has laps and a way out. A plaster wall is one sealed surface, so the coating is what keeps water out.

Will cleaning fix failing plaster?
No. Cleaning maintains a sound coating. Cracks and failed seals are a repair, and weathertightness work needs a licensed building practitioner.

Is plaster really low maintenance?
MBIE says the opposite. Those exteriors generally need more maintenance than a weatherboard house.

If your walls have growth on them, the salt line at the base, or paint you’re unsure about, get a quote and tell us what you’ve found.