Hi all, I'm prepping for a badly needed roof paint on my 4104 and have a question for you knowledgeable folks on at what point paint actually needs to come off. My roof is a mix of bare aluminum, old paint that's still pretty solid, and some paint that's actively flaking. I've already gone over it with a scraper to take off the biggest flakes, then started with 320 grit on a random orbital on what's left. Below are two photos - one of the still-flaky areas, and one that I've given a once-over with a 320 (the bare aluminum was already bare). My question is, is the second photo good enough to follow up with a 600 grit and some primer, or do I need to strip any of the remaining stuff down to bare metal? I could probably get some of the remnant up by picking at it with a fingernail or scraper, but it's not about to fall off on its own.
Obviously, I'm not going for showroom quality here, I just don't want to have to re-do this in a year or two. I'm also planning to lay down some lap sealant along the rivets and seams.
(https://lh3.googleusercontent.com/pw/ACtC-3dJXScliM8c6XLkIufJqILm0Wf353Nat20qq9f1WFwHDfnxEWpGK2QLdIrOMZ7C_a15Yw3_JVh3RbtgwP5L4zVbmJCgJJ2GpF0KIdyYmPuk053445pGZuppymmrcfaV2u3LknA3-prIP267GgN0IESF=w727-h969-no?authuser=0)
(https://lh3.googleusercontent.com/pw/ACtC-3fG6hSyLj_J6g5UJGcFl-klndQ73HXjbg2HpRuoAivEnEcBjC9h-kTWgzqUcAHhdM0XHqJA1bC_dH5Hwzep2WPPgZ7dhuMqMQ1sP9L8OnODxmdBx10fprLr0hWWDrTZhfcqA-b9f63IcwlbeAX50YB9=w727-h969-no?authuser=0)
Forget 600 grit. Too fine. Use something like 180 or 220 with orbital sander. A small needle scaler with light pressure around rivet heads.
I would even go to 60 grit or 80. Then skim with filler any you can't get off sand in with 320 and hit it all with Epoxy primer then use Tropicool roof coating paint. Home depot has it in 5 gallon buckets. It paints it and add insulation reflection to help cool down the Bus more. Just an idea. Or you could use bedliner too. :)
the picture shows paint that was applied without proper preparation of the surface.
You need to sand all of that, and what's under it, into oblivion.
It will be lovely afterward.
Happy coaching!
Buswarrior
For the best job, take it all off, I went with Bus Kote, primer, roof coating, clear coat.
Soda blasting will do the job, but will cost more than you are probably want to invest in compressor, hose, soda, and gun.
A good aircraft stripper will work and 3M makes a tool for the rivet heads ,we feel for you it's a lot of work
I guess it depends where you live as to what chemicals are going to get into the ground.Also, the mess from the liquid stripper. They sell a hand held sand blaster that holds about a quart of media blast material. If you have a decent air compressor, it will work nicely around the rivets, at least. Glass beads will work fine. Will sure make the job easier. Harbor Freight sells media material.
Quote from: chessie4905 on September 20, 2020, 06:33:27 AM
I guess it depends where you live as to what chemicals are going to get into the ground.Also, the mess from the liquid stripper. They sell a hand held sand blaster that holds about a quart of media blast material. If you have a decent air compressor, it will work nicely around the rivets, at least. Glass beads will work fine. Will sure make the job easier. Harbor Freight sells media material.
I don't think you can buy air craft stripper any more with deadly chemicals,the fumes were the problem with people not wearing the right protection it's not really that messy if you let it do the job before scraping it off lol you and Harbor Freight that little sand blaster is a joke
Hah, I was afraid y'all would say that! Now, I intentionally picked photos of some of the worst sections of paint - there are plenty of places where it's solid throughout without any signs of flaking; would that really need to come up too? I'm going for 'good' not 'best' in this case, as I live in New England and am trying to work outdoors in a relatively small window of time over the next few weeks where it's cool enough to be on the roof all day but not so cold that paint won't set. Trying to avoid bringing a bare roof into winter if I can help it.
A few years back I had a guy come with a water blaster to do the whole bus it took him about 5 hrs and $600.00 it was ok but I still had a lot of hand work to do in some areas
Cliff, I wasn't talking about their sandblaster, just the media. There is a small sandblaster that has been around for years that works nicely on small bad areas. Be careful on any chemical strippers. If they get on the anodized sides, it will stain the siding. If you just remove the loose and flaky areas an elastomer coating suggested will cover fine and thick enough to cover imperfections, at least up on a coach roof. If you have concerns about adhesion, wash roof thoroughly when done with a detergent and water. After dried, apply Zinzers alcohol based primer. It covers really well and won't flake off, like water based primers. It dries fast in about 20 minutes or less. Then apply your chosen top coat. Those roof coatings for campers are pretty durable. Or if you want a fast solution, paint roof with a premium quality household exterior latex house paint. I used it on my previous ACF Brill, and it still looked good 10 years later. Paint mfgrs. do a lot of research to make durable exterior house paints.
One of these work great in removing scabby paint areas. Not a cure all but they are cheap, available on Amazon too. Have used them for years. They also make a smaller version that works well in tight areas. You pull it across paint, not push it.
https://www.reddevil.com/index.php?l=product_detail&p=828
Quote from: Nova Eona on September 20, 2020, 07:17:33 AM
Hah, I was afraid y'all would say that! Now, I intentionally picked photos of some of the worst sections of paint - there are plenty of places where it's solid throughout without any signs of flaking; would that really need to come up too? I'm going for 'good' not 'best' in this case, as I live in New England and am trying to work outdoors in a relatively small window of time over the next few weeks where it's cool enough to be on the roof all day but not so cold that paint won't set. Trying to avoid bringing a bare roof into winter if I can help it.
"Good" is what you do before you primer (take it all off), get the best Aircraft stripper you can find and it will go fast. "Best" is the finish you lay down after you primer. Mask off the coach and do your do diligence to please the Environmentalist's.
You can answer and decide fairly easily. Take a paint scraper or sharp putty blade and scrape the "good" part. If the current surface paint is not strongly bonded to the underlaying layer(s), you will have your answer in 5 seconds. Any peeling or chipping or sign of the surface coming apart is the definite sign you need to remove it all.
As mentioned there are numerous acceptable options. You'll probably just need to stew a bit and a few ohsiites then just commit to the extra prep work. This sort of project is 85% labor ad 15% fun actually laying down the paint. You don't need to base/clear, just a solid single stage is fine.
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
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.
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.
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.
Go to an automotive paint supply shop. They will get you the right primer. Rustoleum is not the best.
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.
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.
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.
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.
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.
(https://lh3.googleusercontent.com/pw/ACtC-3eZij-eKuUq39tudQSKrmd1bCjQcewUF1_d9YBWcGyfRmeb0dsy-x6pL2fLqXNZJOqvxiPxvjqeAAQd3EBZBoTvakKldrx6Zai6I8y4bKuXtSrlfMPU8jepSNo8gKAmpI-DofmB3jxZbi2tHKaM3lQD=w727-h969-no)
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.
Looks to me that the yellow is the original zinc chromate primer. I'd leave it there if it has good adhesion.
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
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