Zinc vs. Iron Phosphate Revisited

Question:

I completely agree with your comments (Zinc vs. Iron Phosphate) that zinc phosphate is superior to iron in tough environments. As your colleague Carl Izzo says, “when I had a real job” in paint technical sales, I was a supplier to a very large hollow metal door manufacturer on Long Island. When his customer called for zinc phosphate, he bought a paint product that contained 90% zinc pigment. It was supplied in one gallon cans. Unfortunately, I cannot remember the product name or manufacturer. He would spray this product on the cleaned steel doors. His basic cleaning consisted of spraying an iron phosphate solution on the doors first, drying the doors and then applying the zinc coating. He then would apply the gray primer that I supplied. The vendor that supplies P.K. would not have to change his basic iron phosphate. S.B.

Answer:

Thank you for the support. I have not found anybody else to take issue with the zinc versus iron phosphate question. I believe that it is conventional knowledge that the zinc phosphate will provide more corrosion protection than the iron phosphate. However, you also bring up an interesting option to the reader currently performing iron phosphating. Iron phosphate followed by the use of a zinc-rich primer would also supply very good corrosion resistance since it would essentially be like cold galvanizing a steel surface. That way, you would not have to make the investment in time and possibly additional equipment and maintenance to gain the corrosion prevention benefits of the zinc phosphate pretreatment system.