Do I need a primer on a galvanized steel pole?
I am a construction manager in the electrical field and I represent the purchaser of round, tapered steel street lighting poles that are galvanized. I have purchased the aforementioned poles and now must write a contract to have them powder coated.
The specification that I have for finishing them includes cleaning and a chromic acid sealer, a zinc chromate powder undercoat, and a polyester TGIC topcoat. The specification calls for a 10-year warranty with useful life of 30 years.
A prospective job shopper contends that the specification is either excessive, redundant, or counter-productive. Please advise.Dominic Caputo
Taguig, Metro Manila, Philippines
Galvanizing by itself offers a great deal of corrosion resistance, but paint doesn't stick to it well at all, especially if it has a chromic acid sealer. You need at least a primer designed for galvanized metal, whether it be a liquid paint or a zinc chromate powder. This has been a pretty common question here, so we've added a FAQ about this subject. We hope it helps!
Ted Mooney, P.E.
Pine Beach, New Jersey
Substitute (excessive, redundant) with robust, and I like it. Counterproductive must mean that the combination of treatments actually creates a coating that is less corrosion resistant than a simpler one. Did your supplier tell you what s/he meant by that remark?
Perhaps the job shopper means that the same protection can be achieved with other coatings which they can provide. This requires another specification, or research, perhaps a search of the literature, to see who is correct. If you give us the reference you have for the coating, it would go a long way in generating an answer to your question.
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