Yet another roof painting prep question

Jim Blackwood · September 21, 2020, 09:29:53 AM

I'd say, once you have bare metal the most critical part is the primer. Back in the day the USAF was all about zinc chromate on aluminum which had a distinctive green color. But there may be something better these days. The thing about the aluminum is the oxide layer that forms on exposure to air. You need a specialized paint to deal with that.

Jim

chessie4905 · September 21, 2020, 10:02:28 AM

That is correct, but Zinzers alcohol based primer will work in his case. He doesn't want to spend a lot of money, and time is of the essence this fall. Zinzers is available off the shelf at Lowes. Make sure you don't get the water based version. Check label.

Nova Eona · September 26, 2020, 11:06:34 PM

Is alcohol-based the same as shellac-based? Looks like there's the Zinsser B-I-N primer, not sure if that's the one. I've been reading that self-etching primers were key for this, so was thinking of using a bunch of rattle-cans of the Rustoleum Self-Etch, but advice on this is welcome.

For the top coat, I'm planning on Henry's Dura-Brite - I don't want to lock myself into a silicone base or pay the extra for the fancy variations since I'm not full-timing it, and it sounds like Dura-Brite's generally considered a solid midrange option.

chessie4905 · September 27, 2020, 05:00:53 AM

The base of Zinzers is alcohol. Base of shellac is alcohol. Have you any idea how many rattle cans it will take to do a roof that size? Your index finger will be cramped before half way. Yes, that Zinzers bin is the one.

lostagain · September 27, 2020, 06:47:03 AM

Go to an automotive paint supply shop. They will get you the right primer. Rustoleum is not the best.

richard5933 · September 27, 2020, 07:40:50 AM

I'd agree about an auto paint supply store. Most of the stuff available in the box stores either doesn't stick well enough or can be lifted by the top coat if you use a non-compatible product.

Building a relationship with the folks at a small mom & pop auto paint supply is probably a good idea for anyone with a vintage vehicle, especially a bus with so many different needs. The guy I work with is able to make recommendations for things I didn't even know existed, and he's able to put almost any of his products into a rattle can for me if it's just a small project.

windtrader · September 27, 2020, 10:16:32 AM

DTM is what you are looking for bare metal - stands for Direct To Metal. A two part epoxy primer IS the proper material. Tamcopaint.com is an excellent source of vehicle paint materials. There are prices are very good due to low overhead, and they they manufacturer their own paints, yes, in the USA. Call them. If Tammy answers you got the queen of paint. Spray is their expertise, not sure about rolling.

Nova Eona · September 29, 2020, 08:37:23 AM

Has anyone ever used marine primers? I'm trying to find a primer I can roll on in non-shop conditions, and it seems most of the nicer epoxy primers would really prefer you spray it on in a paint booth.

Researched the Zinssers BIN primer and it sounds like they don't recommend it for anything but spot priming because it dries brittle, so I could see that being problematic on some of those big curved panels.

richard5933 · September 29, 2020, 08:50:14 AM

Lots of options for bare metal primer, including sand-able and not. To my thinking, if you are concerned about possible problems from 'non-shop' conditions it would be best to use a sand-able primer so things can be more easily corrected.

Nova Eona · October 11, 2020, 11:20:55 AM

So after much trial and error with chemical strippers, turns out the absolute best thing I've found for taking off most of the paint has been a razor-blade scraper, peels it off like you're shaving a pencil most of the time. I've now got one side and most of the top clear, but have a question for you knowledgeable folks. In the photo below, you can see the panels are mostly down to aluminum, but there remains a bit of yellow coloration left over from the original primer - is it worth taking off these last remnants as well, or is it safe to assume that anything which has survived a scraping followed by a few passes with 80 grit isn't going anywhere? I do still need to clean up around the edges, seams, and rivets some more, so don't base your answer off those locations.

Primer-wise, I think I'm going to go with the local Sherwin Williams guy's suggestion and use their Pro Industrial Pro-Cryl primer - it's rated for aluminum, doesn't require mixing, can be rolled on, and doesn't require shop conditions to set properly.

usbusin · October 11, 2020, 12:59:33 PM

Looks to me that the yellow is the original zinc chromate primer. I'd leave it there if it has good adhesion.

Dave5Cs · October 11, 2020, 01:05:45 PM

This is what I used and worked great with single stage over it. Sprayed it all outside in 87 degree weather. No problems.

https://www.amazon.com/Speedokote-Primer-Sealer-Gallon-SMR-260G/dp/B016QP0X8Q/ref=sr_1_5?crid=3VV9IP2R1XX32&dchild=1&keywords=epoxy+primer+automotive&qid=1602446640&sprefix=epoxy+primer%2Caps%2C222&sr=8-5

Iceni John · October 11, 2020, 08:20:14 PM

When I completely repainted my bus roof a few years ago I used a putty knife and a heatgun on High, and did one small section at a time on hot days when the roof was almost too hot to touch. Yup, I got a good tan. Whatever didn't scrape off stayed on, including some greeny-yellow primer that I guess was zinc chromate. I then sanded that section of mostly-bare aluminum with a medium-grit sandpaper to roughen the surface, immediately washed it down with an acetone-based degreaser, then immediately rolled on Marhyde self-etching primer ($100 per gallon!). After recaulking all the seams with 3M 5200 I used Rustoleum clean-metal primer, then two coats of Rustoleum gloss white with the magic pixie-dust in it, then two more coats of plain gloss white to make the surface less suede-like and smoother.

John