Epoxy or Etch?

jcclark

jcclark

Oldtimer
I haven't use etch primer in over 25yrs, BUT!
I painted a stripped aluminum boat with etch first, then urethane back in the early 90's,
(The etch was a 1K product)
Several yrs later I repainted it, sanded the paint, sprayed epoxy, then used urethane again.
Worked great and held up well. But then several yrs later I wanted to change the color
so I stripped it to the aluminum with stripper first, well, the urethane and epoxy came off easily,
but the etch wouldn't budge, I had to sand it off.
So does that mean for bare aluminum etch would be stronger,better than epoxy?
I may be painting bare aluminum again.
 
it means that etch is a bad substrate for epoxy. Epoxy already has a slight amount of acid in it for it to bite the metal, doesn’t need any more. The etch likely reacted with the epoxy and affected it’s adhesion. More importantly, the epoxy is a better substrate for your topcoat. Etch is yesterday’s technology. Go with epoxy.
 
well the etch wont typically wrinkle up when stripper is put on it because its a 1k product. it has no chemical resistance. it just soaks in the solvent and rewets itself. epoxy only on a boat
 
Ppg has a tech sheet that has been out for years, and it says never use epoxy over etch because of the acid loss of adhesion will occur.

I think the date on tech is 2008
 
Like I said, I never used epoxy over etch, the epoxy was over the urethane.
I never said anything about a reaction or adhesion problem, there was NONE!
What are you all reading?
The paint held up fine in all cases, it was repainted because
of the scratches the paint gets fishing in the stick ups and I wanted a color change.
The etch never even softened with the stripper.
 
@jcclark , if you want to use 1K etch based on your own personal experience, then maybe you should. But you ought to know that such a plan isn't going to get a warm reception here. We've all spent years trying to get people to stop using the stuff because it causes more problems than it solves. Even if in some niche application like yours where it might be fine, we wouldn't want to give newbies the wrong idea and undo all the hard work we have done trying to stamp out the use of 70's technology.
 
I'm not advocating etch, I'm just asking about why
it held stronger than epoxy on my own boat.
I'll check elsewhere.
 
JC, if my memory serves I don't think most of common available strippers would lift certain etch primers. I've encountered it where you use a stripper on the paint and everything goes but the etch. Don't think it's adhesion as much as it doesn't react to the stripper. I've used some very powerful strippers, the kind that one little whiff will literaly take your breath away, and light you up if you get it on your skin, not to mention "sensitive" areas.:) Stuff that isn't available now and I would encounter that.
Funny thing though you could wet a rag with solvent and wipe it off. Usually I would just sand but it would wipe off with lacquer thinner. Think most of what I encountered was factory etch, but I can remember the green etch on stuff and stripper wouldn't take it off. Never really worried about it cause like I said I just sanded it off.
Like I said probably more due to it not reacting than to adhesion.
 
Methylene Chloride, the active ingredient in most paint strippers, will liquefy 1K products, but wrinkle the snot out of 2K products and then rapidly evaporate. So you can scrape the 2K stuff off, but the 1K may have re-solidified, depending on conditions.
 
Funny about liquid strippers and some coatings. This week I've been stripping a '70 Triumph 650. Have old school readi strip, it's hot. The old red amateur re paint wrinkled right up, prob alkyd enamel. But the original finish which was nitro lacquer was harder to dissolve and remove. Had a weird blue factory primer that im sure is lacquer that wouldn't even liquify, wouldn't budge, and the black striping acted more like a tar or shellac and may have even been a sign paint type of product like 1 shot. Interesting what the Brits used on these bikes even as late as 1970.
That said, when I worked in a local aircraft factory in '76 we still sprayed butyrate dope on almost everything.
On the bike, I still have a rear fender to go. Outside I can wear off with 40g DA, but the concave underside is a royal pain in the ass.
 
JC, I understood your question from the start but I hadn't replied. And yes, I've found that most etch and zinc cromate primers don't dissolve or lift with stripper. I too always found that odd but it's just the chemistry of the coating and the stripper. Even though it's tougher to strip with chemicals, it's been shown to have adverse effects on metals in the past few years, even though after painting many light aircraft and boats over the years I've never had a problem with chromate or etch primers. But if it were me I would use spi epoxy on bare alloy any more. I'm totally sold on this spi epoxy, sprayed some on the bike this week, unlike any epoxy I've ever used.
 
JC, If I am following correctly, the point is not that the etch would not stick but that other materials would not adhere well to the etch. Especially epoxy. You mentioned yourself that the epoxy came off the etch easily, did you not?

Correct me if I misunderstood something.

John
 
John if I understood JC's question correctly, I think it was that when using stripper the epoxy reacted to the stripper and lifted while the etch did not. Think Crash in post #9 addressed why that is.
Correct me if I'm wrong JC.:)
 
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