|High strength, does not warp or crack, not susceptible to movement due to moisture… Sounds like a new generation building product! What is it? It is steel! And while it has many wonderful properties for building, it is subject to corrosion. Corrosion is steel’s enemy!The use of steel for structure and connections within buildings in New Zealand is widespread. Unfortunately, many parts of New Zealand experience a marine environment and most of us choose to live near the sea. Auckland with its high annual rainfall, high humidity and surf beaches on both coasts, as well as the Waitemata and Manukau Harbours is an ideal environment for rust to occur.|
It is therefore imperative in Auckland, that when steel componentry is used in buildings, an appropriate corrosion protection mechanism is in place.
There are a wide range of protective coatings available, the best known being galvanising. There are also a large number of paints that incorporate mechanisms to protect steel. In considering which coating to use, the following factors must be considered; where is it to be used – interior or exterior, what is the environment, can it be easily maintained, what is the size of the component to be coated and how long is the component expected to last? Sound principles should also be applied to the preparation and application of the paint as even the best coating will fail on poorly prepared surfaces. A quick rub with sand paper or a wire brush, and application of paint before the dust settles is not acceptable to provide high performance protection that is required in exterior marine environments. A general rule is off site preparation and application of coatings will achieve the best results – the last coat may be left to be applied on site.
The good news for building owners is that with the advent of the Building Code, the structure of buildings is required to be durable for 50 years, there is a statutory obligation forcing designers and builders to reconsider their approach to corrosion. The building industry is gradually coming to grips with the problem but there are still many poor practices being adopted. One particular reoccurring concern is the use of galvanised joist hangers in external situations. These are manufactured from galvanised steel sheets used for roofing and will not last fifty years. Fortunately, stainless steel brackets are now available but, as with any steel component, inspection and washing from time to time is advisable.
Maintenance is also an essential part of caring for steel work and, in particular, unwashed areas, such as the undersides of gutters which should be washed on a regular basis to remove the build up of salt deposits. If left, condensation on these surfaces will cause rapid deterioration which, in tandem with dew, will cause rapid corrosion.
Like a well maintained car, steel components in a building can have an extended life with :
Sean O’Sullivan is a consultant who has long experience in building design, is a Registered Building Surveyor, being a member of the New Zealand Institute of Building Surveyors and is a BRANZ Accredited Adviser, and also the representative member from Prendos at the Australasian Corrosion Association. Sean completed an ‘A’ pass in a Certificate course in Coatings Inspection.
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