“Rotting” Steel a Problem
by Mark Williams
You have likely heard, seen and even know a fair bit about rotting timber framing, a big and at times even sensational feature of New Zealand’s “Leaky Building” debacle. But, YES, you guessed it ? there is more! A significant number of structures, mainly commercial, but including a proportion of residential dwellings, are constructed with steel stud framing.I can hear you asking yourself “is Prendos saying that steel framing can rot?”, “Surely steel is a ‘saviour’ in this “Leaky Building” syndrome?”, “Steel couldn’t rot!”. Or could it?

A disturbing thought, not only that steel framing may not be above and beyond the vagaries of leaking, but even more disturbing if you are living in a high rise apartment block that is leaking and has corroding steel studs. Corrosion is quite definitely “rot” where steel is concerned.

As we are all aware, and some more than others, there are a number of reasons why buildings leak. Prendos has a strong arsenal of techniques for not only finding the often illusive points of water entry, but also of understanding the mechanisms of why they occur. Most of the leaking buildings Prendos has been involved with, have been timber framed. However, we have now developed a suite of robust tools to find and uncover leaking and corrosion of steel framed buildings. Suffice it to say, in this short expose, that Prendos is confident of its knowledge base in this emerging problem, with its high success rate underpinning the processes used.

Of more interest are the effects leaking has on steel framed buildings. Let us take a generic cladding fixed by screws that hold the cladding onto the framing. Ignoring the effects of leaking on the cladding material itself, we find a number of issues that could affect the serviceable life of the cladding and its ultimate ability to retain its integrity and keep the weather out.

Moisture within a cladding invariably migrates and sooner or later arrives at the metal fixings. Most screws have a thin protective “anti-corrosion” layer that will protect them from the odd small bouts of wetting as long as they can dry quickly. The reality of screw fixing on the other hand is that in the twisting process they exert a significant grinding force on the materials they pass through, in particular another metal like the steel studs, and their outer layer becomes scratched or even removed across a few screw threads. The rest is history, with corrosion setting in rapidly and the result, a compromised and likely sub-strength fixing, destined to failure.

Focusing on the steel stud now (approximately 0.55mm thick), a similar issue occurs when a hole is drilled through the thinly galvanized/plated side wall of the framing. The edges of the metal are left “untreated” and quickly corrode where these become wet.

As the corrosion of the metal continues, so its physical properties break down and the fixing hole “grows” larger becoming a looser fit around the fixing, with obvious consequences.

The disturbing combination of corroding screw fixings coupled with corrosion of the steel stud around these fixings, means the point of failure is likely to occur far quicker than one would expect if compared to “normal” rates of corrosion.

The effect of failed cladding fixings means the cladding as a whole, or in places, could slump down the face of the building, crack, leak further and may even delaminate from the structure.

The primary aim therefore is to identify and stop the leaking with a well considered and properly executed repair.

Having hands on experience in finding, undertaking and directing repairs to steel framed buildings, Prendos finds itself well positioned at the forefront of yet another emerging reality, in the “Leaky Building” syndrome that has plagued New Zealand.

MarkMark Williams joined Prendos in July 2002. He obtained a B.Sc in Building Science from the University of Witwatersrand in Johannesburg in 1987. Ten years later, in August 1997, Mark and his family immigrated to New Zealand and have lived and worked in Auckland for the past six years. Mark has been actively involved in the New Zealand construction industry for the past five years and his experience spans a multitude of projects from commercial subdivisions through commercial buildings, roading, warehouses, a retirement facility, pharmaceutical and biotech facilities. He is experienced in the design, cost control, budgeting, procurement and construction delivery of all of these projects and associated on-site experience.

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