REGULARS: QUALITY MATTERS
It is possible to manage the impact of corrosion by applying a
rust-inhibitor coating.
depending on the environment and the
chemicals, liquids or substances
surrounding the steel.
Essentially there are two forms
of corrosion:
1. Wet corrosion – This is an attack on
the metal caused by water.
2. Dry corrosion – This is generally a
chemical or gas attack on the metal.
Both corrosion types show the impact of
corrosion in different ways, some are easy
to see but some corrosion results are not
easily detectable.
Preventing corrosion
Steel can be coated in many different ways
to withstand the impact of corrosion,
whether it is a metal coating such as zinc
that forms a skin across the bare metal such
as galvanised material or whether it is
chromium alloy such as stainless steel.
These coatings are relatively easy to add
or form in its natural state to provide the
metal the ability to withstand the impact of
corrosion for differing amounts of time and
within different environments, but what
about where the material is on site in its
permanent position or over time the
material has lost its coating or ability to
withstand the corrosive attack?
We can all visualise a ‘rusty roof sheet’
and the client is left in a position where he
either must replace the steel roof sheeting
or apply a coating. In some cases, the
removal of the roof sheeting can be
problematic depending on the operation
within the building. In this circumstance the
client is left with a choice of coating the
A corrosion coating provides a guarantee of up to (and even more
than) 10 years.
steel sheeting or to over-roof using a
structural spacer system and an additional
roof sheeting layer.
A careful environmental analysis of
refurbishing the existing roof / cladding
system can lead the specifier to the
decision that a coating or over-roofing /
cladding system may be beneficial to all
parties, when comparing the environmental
cost of the production of the coating
against the production of a new coated roof
sheet. With the over-roofing system the
ability to add additional uncompressed
thermal insulation provides significant
thermal performance that will reduce the
operating costs of heating, ventilation and
air-conditioning (HVAC) systems and reduce
carbon footprint.
To coat or not to coat
Should coatings be the route that the
specifier wishes to embark upon then
‘rust-inhibitors’ or ‘corrosion inhibitor’
coatings need to be considered.
A corrosion inhibitor is a chemical that
when added to a liquid or gas, decreases
the corrosion rate of a material. A common
mechanism for inhibiting corrosion involves
formation of a coating, often a passivation
layer, which prevents access of the
corrosive substance to the metal.
Most rust-inhibitor coatings when
applied, will remove the moisture from the
corroded area and then seal it off so that
moisture and air cannot have an impact on
the steel material any further or until the
coating breaks down. Accurate application
of such coatings is reliant on correct
preparatory work to ensure that the area is
clean before the coating is applied.
Steel can be coated
“ in many
different ways
to withstand the impact
of corrosion.”
It can be the case that in certain areas the
corroded metal needs to be removed and
new steel put in its place. The application of
the coating will have the biggest impact on
how the coating performs on the affected
area. If the area is poorly prepared before
application, then corrosion will quickly
appear through any coating.
There is a vast range of rust-inhibitors
and choosing the correct application is
dependent on the extent of corrosion, the
environment and the chemicals
surrounding the area of rust. The chemical
composition of some of the coatings are
more environmentally friendly than others
with some systems boasting no lead, no
zinc, no chromates, no acids and no heavy
metals making these coatings friendly to
the environment.
The option of these rust-inhibitor
coatings gives the specifier the opportunity
to lengthen the operational life of roof,
cladding or steel structures without having
to strip and replace. Certain rust-inhibitors
can provide a guarantee of more than 10
years depending on the environment and
the state of the corrosion.
MRC Group has used rust-inhibitor
coatings on a myriad of different projects,
sectors and applications providing the
client with an extension of life on the
materials that encapsulate the building.
RESIDENTIAL // COMMERCIAL // INDUSTRIAL
APRIL 2018
29