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Colorcoat® Column: Marine Environments

27 April 2009 No Comment

Question When specifying cladding systems for the construction of a building envelope in a marine environment what material would be best? Would it be aluminium?

Answer  Firstly we should define what we class as a marine environment. Under the Corus Confidex® Guarantee (available only with Corus Colorcoat Prisma® and Colorcoat HPS200® Ultra) it is classed as a building that is within 1 km from any coast. Generally aluminium is tolerant of PH values between 4.0 and 8.5 at room temperatures forming a film of hydrated aluminium oxide on the surface. A saline environment could mean a risky environment for the use of mill finished aluminium. A marine environment can cause pitting to the aluminium surface. The severity of this pitting obviously is dependant on how aggressive the environment it is subjected to. Therefore it is often recommended that painted aluminium be specified. The most common paint employed to coat aluminium is PVDF.

We at Corus do not recommend the use of PVDF on zinc coated steel substrate in marine environments as they offer markedly inferior performance. This is due to inherent coating permeability, which can lead to under film corrosion of the zinc and causes paint blistering particularly in stressed areas such as profiled bends.

Corus recommends that in saline environments a high build protective system such that is offered by Colorcoat HPS200® Ultra. The 200 microns thickness provides a more effective barrier against the permeation by salt polluted moisture than thinner coatings such as PVDF (27 microns thick). Furthermore, the excellent damage resistance of Colorcoat HPS200® Ultra is of particular advantage where a potentially aggressive atmosphere can readily attack steel substrate exposed due to physical damage.

Usually performance figures for PVDF coated aluminium when used in marine environments are in the range of 15 years. Corus offers a Confidex® Guarantee of up to 30 years for roof and wall on Colorcoat HPS200® Ultra. Euronorm 10169-2 outlines requirements for the corrosion resistance of pre-finished steels. The most onerous category, RC5, requires products to resist blistering, coating damage and edge delamination <2mm when exposed to aggressive industrial and marine environments. The unique Galvalloy® metallic substrate from Corus and step change in paint formulation that has been developed for Colorcoat HPS200® Ultra mean that it can easily meet this very high standard.

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