Powder Coating Question, Is primer necessary? Options

[AndrewBlyholder]

Was thinking of having some trailing arms powder coated. Got two estimates from local shops. Cheaper one claimed that they didn't need to put a primer coat on before the finish coat as it wasn't necessary, the finish coat adheres well enough by itself. More expensive shop claimed that an epoxy or polyurethane primer was absolutely necessary. Any advice from the past experience out there?

Thanks,

Andrew B.

[AndrewBlyholder]

Thanks for the primer advice guys. I'm thinking now to just go with the cheaper guy without primer. Both shops were sand plasting the parts to clean them throughly.

My 2 cents on the metal etchers: All these products are generally just phosphoric acid. Check the ingredients list and that's probably what you'll find. Strong versions are also commonly marketed as rust-convertors. The phosphoric acid changes the reddish iron oxide rust to iron phosphate, with a black apprearance. The iron phosphate supposedly is much more tightly bonded to the base metal and won't flake off and acts as a barrier to further oxygen penetration and further rusting. That's the theory anyway. I've used it a lot on various 914 chassis areas that I've stripped and repainted but didn't have the time or energy to grind down to bare, clean metal. Haven't had any problems with subsequent rust breaking out, but I'm located in California, so the climate is not as punishing.

Andrew