Aluminium Joinery and Salt: Looking After Windows by the Harbour

Aluminium joinery is the quiet workhorse of harbourside apartments in Te Whanganui-a-Tara. Window frames, sliding doors and balcony doors take the full force of southerlies, wind-driven rain and a constant fine film of salt, and most of the time they carry on without complaint. That reliability makes them easy to forget. The trouble usually starts in the places nobody looks: the bottom track of a slider, the back of a hinge, the drainage slots behind a sill.

Why harbour air is hard on joinery

Salt is the main problem. Wind lifts spray and fine droplets off the water and deposits salt on every surface it reaches. Salt draws in moisture from the air, so a coated frame can stay damp long after the rain has stopped. Over time that damp, salty film works at any weak point in the coating and at every exposed screw head, spring and roller.

New Zealand’s timber-framing standard, NZS 3604, uses exposure zones to decide how well structural fixings must be protected from corrosion. The highest-risk inland category, Zone D, covers land within 500 metres of the coast, and harbours count as coast. Almost the whole of the inner Wellington waterfront sits well inside that band. The zones are written for framing fixings, not windows, but they show how much salt reaches buildings near the water.

One finding surprises many owners. Sheltered surfaces often fare worse than exposed ones. Rain rinses salt off a frame that faces the weather, but the head of a window tucked under a balcony, or the inside face of a deep reveal, never gets washed. Salt builds up there undisturbed, and that is where coating breakdown tends to show first.

Washing is maintenance, not housekeeping

The single most effective thing you can do for powder-coated or anodised aluminium is to wash it regularly with fresh water and a mild detergent, using a soft brush or cloth, then rinse thoroughly. Avoid abrasive pads, solvents and strong alkaline cleaners, all of which can damage the finish.

How often depends on exposure. Coating manufacturers’ care guides in New Zealand commonly recommend washing at least every six months in salty or corrosive environments such as beachfront homes, and some suggest every three months for the most severe or sheltered locations. It is worth finding the care instructions for the coating on your building, because powder-coat warranties are typically conditional on following the manufacturer’s maintenance programme. A frame that has never been washed may not be covered if the finish fails.

In an apartment block the outside faces of the windows are often common property, or at least only reachable from a lift or rope access. That makes window washing a body corporate decision, and it is worth checking that the cleaning contract includes the frames and not just the glass. The Unit Titles maintenance guidance sets out how responsibility is split between owners and the body corporate.

Hardware: the parts that actually fail

Frames rarely fail outright. Hardware does. A few points to check each season:

Sliding door rollers and tracks

Grit and salt in the bottom track grind away at rollers. Vacuum the track, wipe it with a damp cloth, and keep it clear of leaves and sand. A door that has become heavy to slide is usually a sign that rollers are worn or the track is dirty, and replacing rollers early is far cheaper than replacing a damaged track.

Hinges, stays and handles

Friction stays on awning windows and the hinges on balcony doors are often the first components to stiffen. Wash them along with the frame, check for white powdery corrosion on aluminium parts or brown staining on steel, and follow the hardware supplier’s advice on lubrication. Many recommend a light, non-greasy product rather than heavy grease, which traps grit.

Fasteners and dissimilar metals

Where steel screws or fixings touch aluminium, salty moisture can drive galvanic corrosion. Stainless steel fastenings are the usual choice near the sea, and any replacement screws should match or better what was originally used. Staining running down from a fixing deserves a look before corrosion spreads under the coating.

Drainage slots and seals

Aluminium sills are designed to let a little water in and then drain it out again through small slots or weep holes. When those slots clog with dirt, salt crust or insect nests, water backs up and can find its way into the wall or across the floor. Clearing them is a simple job with a soft brush or a length of wire, and it should be part of every wash.

Rubber seals and gaskets also age faster in strong sun and salt. Look for shrinkage at corners, cracks, or sections that have pulled out of their channel. Our earlier piece on Wellington wind and weathertightness covers how wind pressure exploits small gaps.

Durability expectations

The Building Code’s durability clause, B2, requires building elements to last for set minimum periods of 5, 15 or 50 years, depending on the element, with normal maintenance. That last phrase matters. The durability periods assume a building is looked after, and in a coastal location normal maintenance includes regular washing and timely hardware repairs.

A simple routine

For most harbourside owners a workable routine looks like this:

• Wash frames, sills and hardware with fresh water and mild detergent at least twice a year, more often for sheltered or seaward faces.
• Clean sliding door tracks and drainage slots at the same time.
• Operate every window, door and lock, including rarely used ones, and note anything stiff.
• Check seals for cracks and shrinkage before winter.
• Keep a short record of what was done and when, which helps if a warranty question ever arises.

An hour each season adds years to joinery that is expensive to replace. For more on how salt affects the surfaces around your windows, see our notes on salt air and painted exteriors.