Stucco | Issues you should know

Stucco became a relatively common cladding in Nelson/Tasman in the late 1940s. An alternative to timber weatherboards it offered a solid look, and a more modern, with it, style. It was the days of hope, and Formica.

My grandfather, a builder, built his own home in Salisbury Road in 1947. Construction: a timber frame, Pinex softboard backing, building paper as waterproofing, chicken wire supported on beer bottle tops as the reinforcing, and three layers of cement based plaster. Then it was painted. Galvanised steel cappings for the parapets. The timber window frames had head and jamb flashings, but no sill flashing.

It’s still standing more than 70 years later.

That was typical stucco construction up until the 1990s.

But the 1991 Building Code also allowed for “Alternative Solutions” that have subsequently proved to be poor building practice. Shoddy workmanship, and poor oversight by council building inspectors led to what is known as Leaky Building Syndrome that has an estimated cost of over $11 billion to rectify.

Two common “Alternative Solutions” building systems in the 1990s were the direct fixing of either Hardiflex sheets, or 50 mm polystyrene insulation over a single layer of building paper. These both relied on the integrity of a thick acrylic paint to ensure the building remained waterproof. No cavity, the structure relied on the paint finish to keep the weather out.

When the building moves due to wind or earthquake, cracks can open up because of differential movement between the fibre-cement or polystyrene sheets.

Also, the detailing around the windows, and the fashion for small or no eaves allowed for water to get beyond the waterproofing paint finish and cause deterioration to the structural timber as the wall insulation tended to hold water.

Bad. Bad. Bad.

In general, the Nelson/Tasman buildings are often not as poorly constructed as those of Auckland where cost-cutting became the norm.

Leaky buildings caused a complete rewrite of the Building Act 2004, and an extensively revised Building Code.

The cladding of buildings is now highly scrutinised by councils, both in approving the Building Consent documents and inspecting the real-world constructions.

So, two layers of building wrap. A nominal 20 mm drained and ventilated cavity between. The treated battens are vertical to allow water to drain. Tape to the window openings, then extensive overlapping flashings to the head, jambs and sill once the windows have been installed.

It is presumed the exterior stucco will in fact leak, and that water needs a way to exit rather than getting into the building structure.

Technology for checking water infiltration such as infrared cameras exist, but alternatively, moisture measurements around the windows and skirtings with a moisture meter will give the same result, albeit not as flash looking.

Stucco can function well as a building cladding. The main thing is that all buildings of this type need to have the integrity of the paint finish maintained. The exterior of the house should be checked on a yearly basis, or after any earthquake, and any hairline, or other cracks patched to prevent the ingress of water.

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