Washing Salt off Coastal Buildings

Every building near Te Whanganui-a-Tara collects salt. Spray lifts off the harbour in a southerly, the wind carries it inland, and it settles as a fine, slightly sticky film on walls, windows, frames and fittings. Rain washes some away, but what stays behind keeps working on paint, metal and sealants long after the storm. Regular washing is one of the cheapest ways to make a coastal building last.

Why salt matters

Salt crystals draw moisture out of the air and hold it against whatever surface they sit on. On painted surfaces, that damp, salty film speeds up chalking and can lift coatings at edges and joints. On metal it drives corrosion, especially at fixings, cut edges and scratches. On glass it leaves a haze that dulls the view and, over years, can etch the surface. On aluminium joinery it can cause pitting and white powdery corrosion, particularly in tracks and corners where water sits.

The worst damage tends to happen in places the rain never reaches. Soffits, the underside of balconies, sheltered corners, recessed window heads and the back of downpipes all gather salt and grime without ever being rinsed naturally. These “unwashed” areas are often where coatings and metal fail first.

How often to wash

There is no single rule, because exposure varies so much. A balcony facing straight onto the harbour in Oriental Bay lives in a very different world from a sheltered back wall a few streets inland. As a general guide:

• Directly on the water or in obvious spray zones: sheltered areas every few months, the whole exterior at least twice a year.
• Within a few hundred metres of the coast: a full wash once or twice a year, with a quick rinse of sheltered areas in between.
• Further inland: an annual wash usually does the job.

Some cladding, roofing and coating manufacturers make regular washing of sheltered, unwashed areas a condition of their warranty, and in severe marine environments their recommended interval can be as short as every few months. If you know which products are on your building, it is worth reading the maintenance section of their warranty documents. MBIE’s guidance on building safety and maintenance is a useful general reference.

Rinse, soft wash, or pressure wash?

Most coastal grime does not need force. It needs fresh water, a mild cleaner and time.

Rinsing. A garden hose and a soft brush on an extension pole will shift fresh salt from most surfaces. Work from top to bottom, and rinse thoroughly so you are not leaving detergent behind.

Soft washing. This is the approach most suited to painted and coated surfaces. A low-pressure spray applies a cleaning solution that breaks down dirt, mould and lichen, which is then rinsed off gently. It avoids the damage that high pressure can do to paint, sealants and timber.

Pressure washing. High pressure has its place on concrete paving and some hard surfaces, but it is risky on cladding. It can drive water behind weatherboards and into joints, strip paint, raise timber grain and blow out sealant. On a building that relies on its cladding to keep water out, forcing water in is the last thing you want. If in doubt, turn the pressure down.

Glass and joinery

Windows on the water side need more attention than the rest. Wash glass with plenty of fresh water and a little mild detergent, then squeegee or dry it to avoid spotting.

For aluminium frames, clean the tracks and drainage slots as well as the visible frame. Blocked drainage holes let water sit inside the frame, and salty standing water is exactly what aluminium does not like. Check seals while you are there, and wipe stainless steel balustrade fittings with fresh water to slow tea staining.

Watch where the water goes

In Wellington, the stormwater system is separate from the wastewater system, and street drains and downpipes carry water to streams and the harbour, generally without treatment. Greater Wellington Regional Council has long encouraged people to keep anything other than rain out of stormwater drains. For a waterfront building, the wash water can reach the harbour within metres.

That has practical consequences:

• Choose cleaners carefully. Biodegradable, phosphate-free products are a better choice, and less is usually more.
• Contain what you can. On paved areas, direct wash water onto lawn or garden where the soil can filter it, rather than into a street grate.
• Keep paint out. If washing is preparation for repainting and old flaking paint is coming off, catch the debris. Older buildings may have lead-based paint, which needs particular care.

Greater Wellington and Wellington City Council both publish environmental guidance, and it is worth a look before any large job.

Safety first

Washing a single-storey house from the ground is a reasonable DIY job. Anything involving ladders on a hillside, upper floors, roofs or balconies above a drop is not.

For multi-storey buildings, apartments and anything where access is awkward, getting a professional exterior wash usually makes sense. A good operator will bring the right access gear, use low-pressure methods suited to the cladding, know how to manage runoff near stormwater drains, and spot early warning signs such as cracked paint, failing sealant or corroded fixings while they are up close. For a body corporate, building that into the long-term maintenance plan is often cheaper than repairing coatings early.

Little and often

Salt never stops arriving on the waterfront, so washing is a routine rather than a one-off. A regular rinse, a gentle approach and some care about where the water ends up will keep cladding, glass and joinery looking better and lasting longer. For more on coatings in marine air, see our notes on salt air and painted exteriors.