Surface World May 2019 Surface World May 2019 | Page 18

QUALICOAT UK & IRELAND
Colour fastness of
powder coating
Over time all fi nishes exposed to
weathering will be effected by the
elements, this is especially relevant to
buildings which are rarely cleaned on their
exposed surfaces. On some materials, such
as copper, the green patina effect once
weathered can be very pleasing.
More recently we have seen
Corten exposed steel be used
which weathers to a dark rusty
hue. But when fi nishes that are
intended to be bright colours on
building completion fade over
time, or possibly stain, this can be
seen as a fi nish ‘failure’. So what
about powder coating, how does
it stand up against the elements?
Class 1 powders
After 12 months less than 50% loss of gloss, and colour
change between 2 and 6 delta units (subject to the colour).
This pass criterion is commonly known as ‘1 year Florida’.
Class 2 powders
After 12 months, less than 25% loss of gloss.
After 24 months, less than 33% loss of gloss.
After 36 months, less than 50% loss of gloss.
The formulation of powder coated surface treatments
has advanced over the forty years that powder coating
was first specified for architectural metalwork. Many
of the original projects are still in use today with the
coating still doing its job protecting the aluminium
or steel substrate. Much of the current architectural
powder coating in the UK uses ‘Class 1’ powders
which offer excellent adhesion and long life.
What is little known, is that powders themselves can be
supplied in various grades of durability to suit a project
application. These premium powder compositions
use more expensive and robust materials to offer life
expectancies well beyond 30 years and often similar to
the life expectancy of the building itself. QUALICOAT
has created quantifiable powder performance
classifications for architectural powder coatings.
In Europe there are three distinct classes of
performance - Class 1, 2 & 3.
The key parameter to distinguish the performance of
these Classes is their ‘weathering’ ability. That is to say,
the ability to maintain a consistent colour and gloss
level over time. To ‘weather’ well the coating must resist
the deleterious effects of Light (in particular UVa &
UVb), temperature and humidity. The globally accepted
method for this ‘natural weathering’ test is conducted
in Florida, USA. Sample panels are set for external
exposure at a given angle 5° South. Powders are then
classified on the following performances:
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APRIL 2019
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