Yet another roof painting prep question

Nova Eona · September 19, 2020, 06:48:58 PM

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.

chessie4905 · September 19, 2020, 07:19:12 PM

Forget 600 grit. Too fine. Use something like 180 or 220 with orbital sander. A small needle scaler with light pressure around rivet heads.

Dave5Cs · September 19, 2020, 08:02:52 PM

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.

buswarrior · September 19, 2020, 08:03:45 PM

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

silversport · September 19, 2020, 09:23:10 PM

For the best job, take it all off, I went with Bus Kote, primer, roof coating, clear coat.

chessie4905 · September 20, 2020, 04:26:44 AM

Soda blasting will do the job, but will cost more than you are probably want to invest in compressor, hose, soda, and gun.

luvrbus · September 20, 2020, 05:57:53 AM

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

chessie4905 · 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.

luvrbus · September 20, 2020, 06:55:29 AM

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

Nova Eona · 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.

luvrbus · September 20, 2020, 07:34:13 AM

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

chessie4905 · September 20, 2020, 08:13:46 AM

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.

chessie4905 · September 20, 2020, 10:31:37 AM

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

Van · September 20, 2020, 10:52:29 AM

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.

windtrader · September 20, 2020, 08:06:28 PM

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.