Architects memo no. 2: August 1980
corrosion prevention of galvanised steel
Traditionally the zinc coating of steel has been regarded
as a protective coating in itself, being painted only for aesthetic
reasons. Increased corrosion rates of zinc, particularly in industrial
and marine environments, have lead to the realisation that not protecting
the zinc from corrosion is wasteful of a decreasing resource. Standard
primers for zinc however, do have a number of drawbacks such as:
- They are two-component mixtures; such as zinc dust-zinc etch oxide, two
pack etch primers
- They have very critical recoat times; such as etch primers, calcium
- They contain toxic components, such as etch primers, calcium plumbate
Standard acrylic paints adhere well to galvanised steel but do little
to reduce the corrosion of the reactive zinc.
It was recognised that there existed a gap in the primer range that
could be filled with a particular product conforming to the following
- Would adhere in the short and long term to new and weathered galvanised
- Would passivate the reactive zinc surface to retard corrosion
- Would have a secondary effect as a ferrous metal primer
- Would be a one-pot material
- Would have a non-critical recoat time
- Would be suitable for roofs collecting potable water
- Would be able to be topcoated with a variety of topcoats (such as alkyd,
acrylic, chlorinated rubber)
Although this does appear to be a tall order, these parameters have
all been incorporated in Resene
Galvo One. This product now has a technical history of nine years
and a commercial history of six. It has been widely accepted by specifying
authorities, and is also being manufactured overseas. The possibility
of negotiating further overseas manufacturing rights is presently being
Resene Galvo One is suitable as a lap primer as well as on new or
It can be applied by brush, roller, conventional or airless spray,
with complete safety to personnel. It stops zinc corrosion and effectively
welds itself to galvanised iron while its white colour ensures good
topcoat coverage of gutters and downpipes.
Resene Galvo One has a dry time of five hours at 18°C and can
be recoated after twelve hours. It has a theoretical coverage of twelve
square metres per litre with a dry film thickness of 35 microns. Usually
one coat is sufficient, but where severe corrosion is present an extra
coat is recommended.
The choice of topcoat should be governed by the environment in which
it is being used.
Acrylics are suitable for use in most environments giving adequate
protection with excellent aesthetic appeal. The use of micaceous iron
oxide pigmentation while reducing the colour range increases the protective
qualities. In industrial and severe marine environments, barrier type
coatings such as Resene
Armourchlor HB-F or Resene
Micabond are required to maximise protection.
For further information on this subject refer to the following data
sheets in the Resene One-Line Specification manual: Resene
Galvo One, Resene Hi-Glo,
Resene Armourchlor HB-F.
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