Architects memo no.
71: November 2002
Even the most environmentally benign exterior paint is deliberately
designed to impact on the environment. Paint is engineered to prevent
the natural bio-degradation of many of our building materials by combating
Nature's combined battalions of water, UV light, salt spray, acids,
oxygen and microbes.
There is a lot of focus on UV levels currently with greater attention
being paid to the dangers of skin cancer and concern over the possible
dangers of fluctuations in the ozone layer. Australia and New Zealand
have been singled out due to a combination of our high levels of UV
and our outdoor lifestyles.
Virtually all of the really deadly radiation (less than 300 nanometer
wavelength) is absorbed in the stratosphere by a cycle of interactions
between UV light and oxygen to produce ozone, which further reacts
with UV light to produce oxygen again. However the balance of UV
hitting earth (from 300-450 nanometer wavelengths) can still be pretty
The amount of UV that gets through to the earth's surface varies
enormously with Northern Europe only receiving half the levels that
we in Australasia do. Distance from the sun has some effect and, as
Earth's perihelion occurs in our mid-summer, this will account for some
of the difference.
By far the major effect however is how much UV is absorbed passing
through our atmosphere. Even a perfectly pristine atmosphere shows some
absorption and UV levels at the Equator will be greater than at the
poles. This effect is somewhat offset by longer daylight hours.
Major UV absorbers in the atmosphere are clouds and particulate
matter. Northern Europe's pollution accounts for a lot of the UV attenuation
in that part of the world but natural phenomena such as fine dust in
the atmosphere or smoke from bush fires can also reduce UV levels
Although UV alone is enough to damage human skin, it is a combination
of both UV and moisture that wreaks the most damage on paint films.
It seems that while UV can damage paint polymers, the presence of
moisture at the instant the damage occurs makes that damage terminal.
High humidities, as experienced by almost all of New Zealand and parts
of coastal and tropical Australia, greatly increases the stress on paint
films. Particularly stressful is the presence of dew on a painted roof.
The Australasian paint industry has generally learned to cope with
these conditions and still deliver the required durability. For example,
many of the binders successfully used in Europe have had their shortcomings
exposed in our climes and have been ignored in favour of more inherently
Many typical 'architectural' pigments have limitations in our exterior
environment and Resene in particular lead the way in introducing high
performance 'automotive quality' pigments into their architectural paints.
The quest continues for greater and greater durability.
Just as the human skin can be protected by sunscreens so there are
industrial UV absorbers that can further protect paint films.
Paint degradation is mainly a surface phenomena with only the first
1 or 2 microns of the surface needing to degrade before a loss of gloss
or a change in colour is noticed. The addition of UV absorbers into
the body of a paint is inefficient as very little ends up on the surface.
However if they are formulated into a clear coating and applied as an
overglaze significant added protection is achieved.
This added protection will only be specified when more sensitive colours
are used or when ultra long-term performance is required. The presence
Sun Defier in the range gives us yet another tool to beat off the
effects of our harsh environment.