Better To Use A Primer?
Q. I have iron railings and balconies being powder coated with polyester. They have been sand blasted after their recent fabrication. The powder coater wants to prime with a high-zinc chromate epoxy primer. Is this better than just the polyester? He anticipates a light coat followed by a 4–6 mil finish coat. These parts will be mounted outside in southeast Pennsylvania and the platform grate will be walked on. G. H.
A. Applying a “zinc-rich” epoxy powder coating primer and a TGIC polyester powder coating topcoat will provide better corrosion resistance over steel railings than just a topcoat of polyester alone. be sure your powder coater also pretreats the steel surface using an iron phosphate prior to using the epoxy primer to ensure better adhesion and corrosion resistance.
The iron phosphate pretreatment will provide surface roughness (tooth for adhesion) and a corrosion barrier if the coating is breached. It will increase the corrosion resistance of the coating package by at least two and reduce rust blisters and corrosion creep.
The zinc-rich epoxy primer will protect the steel from corrosion by offering the zinc as a sacrificial metal. The epoxy component will provide excellent mechanical and corrosion properties, as it is the best organic coating for this purpose.
The TGIC polyester powder topcoat will provide excellent UV resistance and good mechanical durability. This formulation also has a reputation for colorfastness and gloss retention that has been proved for many years. Combined, this pretreatment, primer and topcoat package will provide the best overall protection and ensure that your railing looks as good as new for years to come.
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