Originally Posted by 69 widetrack
First off there are 2 types of adhesion, mechanical and chemical, to get the best results both should be recommended. I would rough up any metal, for insurance purposes to achieve a better mechanical adhesion...You've got it there, it's not going to take that long to rough up the metal slightly to ensure a better adhesion, why not do it? If your using etch, I wouldn't top coat directly over etch on a large surface regardless. It's a product that's applied thin and with the expansion and contraction differences in metal versus top coats, a buffer zone of primer like epoxy or 2K, I feel gives longer lasting results. Etch I feel is excellent for small burn through's on edges etc. (I mean small burn through's) and then top coat. So etch still has it's purposes and still sold with good results.
This is a debate...it's the same old story, I did a seminar on this about a year ago and one of the people asked me what I preferred, I told him that I liked epoxy and explained why (as I did in my previous response), another guy stood up and said he did a test, one panel with epoxy (PPG DPLF 40) and one with Nason etch primer, left both panels out in the elements for 1 year and the etch stood up much better than the epoxy, apparently the epoxy lifted around the edges and started to rust.
I asked him how the metal was prepped and where they both prepped the same, he started getting upset and told me of course they where and that it was a stupid question. I asked if he allowed the proper induction time for the epoxy (not required for all epoxy primers but for DPLF 40 you need to mix your primer and let it sit for awhile before apply it)...he asked what induction time was....did this cause the epoxy to fail in comparison to etch, I don't know, I wasn't there to see what happened but if he didn't know what induction time meant, chances are he didn't follow instructions and when they aren't followed your guess is as good as mine.
I've used both, believe in both, but, prefer epoxy for the reasons I mentioned earlier, is one better than the other as far as preventing rust. I'd say rust prevention or minimization is more about prep more than product, they both work if you follow instructions, if you get rust after applying a rust preventative product correctly, chances are you screwed up somewhere else.
I would say over 90% of warranty claims I paid out where not product failure, they where more to keep a good customer that had human failure happen. This is not to say that products don't fail, I remember a clear coat from a major manufacturer in the early 90's that consistently yellowed, that was product failure and was recalled and warranty was paid, but that is more uncommon than common.
Hope this explains the differences between the 2 products.