Heavy duty coatings may be defined broadly as those coatings which are applied at high film builds in order to provide exceptional durability and resistance to particularly aggressive environments. By this definition, they are not explicitly anticorrosive coatings (already discussed in a previous column in this series) but include complete systems with anticorrosive primers.
Three-coat systems with a zinc-rich primer, an epoxy intermediate coat and two-pack polyurethane topcoat can be considered as a point of reference for heavy duty coatings applied to metals. The dry film thickness will generally be in the range of 200-350 µm. This high build is required partly to ensure that peaks on rough steel profiles or concrete are actually covered by something as well as to minimise the penetration of any contaminants to the substrate, provide resistance to abrasion, impact, severe weather conditions, corrosive atmospheres or liquids. Barrier-type pigments such as micaceous iron oxide, glass flake or aluminium flake may be incorporated to enhance levels of protection.
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