I can't tell from the picture, but did the paint peel from the primer, or did they both peel off the metal? If the former, then maybe using high-temperature paint over the etching primer would work better.
The PRIMER peeled away from the METAL. The etch primer and the paint were very much still stuck together. So to answer your question: the paint and the primer were stuck together pretty good, but they both peeled off the jacket together.
Harold, yes sanding the primer is a good idea. for one it creates a mechanical adhesion and open up the pores in the primer which the paint will adhere to.
PontiacGuy, what type of metal did you use and what type of prep work did you do to it?
-Kevin S.
The material was Galvanized steel. I sanded it down with 120 grit twice, and then again with 200 grit. The guys at the paint store told me that the etching primer would be needed to adhere to the zinc in the galvanized surface. I sanded three times, prepped it with thinner, and then primered it with the etch primer. I then let it dry for a couple of days, lightly sanded it with 200 grit, and then sprayed the paint over top of that. The guys at the store said that this would handle the heat, and it definitely did not.
Now, I do realize that the zinc in the galvanization has a lot to do with the failure. I bought this particular type of primer specifically for this use, telling the paint professionals exactly what the conditions would be and what the surface was, and it failed spectacularly. It looked great as I was firing up, it looked great as I was running it, it looked great when I shut it down, but then when it had cooled, the paint peeled off in huge flakey layers, from the primer.
How did I fix it? I removed the jacket and sanded it until all of the zinc coating was gone. I sanded it until the metal changed color, then I went back and sanded it down again with 200 grit to smooth it up (LOTS of sanding). I then painted it directly on the metal with a high-temperature black paint, no primer. I ran the locomotive 4 or 5 times and the paint held up well. The paint I used said it did not require a primer.
My point about all of this: I don't think that most of the etching primers will be able to take the heat/cold cycles of a typical boiler jacket, and you'd be better off staying away from them. Another point: Don't use galvanized to make your jacket! I did because that was all that I could get at that time. It was a huge pain, but I think the jacket is now the best that it can possibly be: Galvanized on the inside and painted on the outside. A really good method would be to use single-sided galvanized and put the galvanized side on the inside, if you could get that material, which I doubt you can.
Hope this helps to clarify what was going on. Bmalone knows all about that locomotive and the troubles I had getting the paint to stay on it. Also, I don't use any type of lagging under the jacket, so it will get hotter.
Why do I not use lagging? I've pulled apart several locomotives that were lagged and the lagging had gotten wet and held that moisture, making a huge rusted up mess. It rusted out the jacket in a few places, and made a mess of the outside of the boiler. I would rather not have lagging and have any water drain out of the thing so that it doesn't rust. I have always felt like a very thin layer of lagging wouldn't make a noticeable difference in the performance of the locomotive on a typical day, but the absence of it would make the locomotive less prone to corrosion as mentioned above.
Chuck Hackett did some experimenting with lagged versus no lagging and found virtually no advantage in filling the space with anything. The thinking was the air was just as good an insulator as any of the common materials. If I remember everything correctly.
I believe his data is floating somewhere on the ether, perhaps on his webpage.
Very useful info as I start to make preparations to replace the jacket on my Allen 2-4-0. Has anyone experimented with using high temp stove paint on the inside of a non-galvanized boiler jacket to prevent rust as well? Nervous about the nasty zinc dust from sanding galvanized steel.
Why nervous about zinc dust? I've welded a fair number of galvanized items with a properly fit respirator and appropiate cartridge I have had no issues. The particulate size from welding will be much smaller than if you are sanding it off.
Not that I am suggesting that using galvanized material is the way to go, I hate the stuff, but rather if the proper precautions are taken there is nothing to be afraid of. That being said if one does not take the proper precautions you have 'zinc chills' to look forward to. Ask google if you want to know more about 'zinc chills', they are not fun.
Zinc is not as dangerous as everyone thinks... As long as you take a few precautions. If you are going to sand it off, just go get yourself a decent dust mask (filtering face-piece as they are properly called), and then go for it. Probably an N95 (which means it filters out 95% of the airborne particulates) will be more than enough. Get one that is comfortable for you, and the ones with the exhale flap are better in my opinion. If you buy them in a pack of 5 or 10, then just store the rest inside of a zipper type freezer bag, and they'll be good when you are ready for them again.
I was just working with what I could get my hands on right at that time. The local place could have gotten me some non-galvanized stuff, but I would have had to order an entire 4'x8' sheet of it. I only needed less than half of a sheet, and didn't really have anywhere to store the remainder where it wouldn't rust or get damaged.