Finally painting the roof! Any last minute advice?

[Geom]

Well it's taken me two months to get somewhere I can work on the roof repainting project and the weather appears to actually be cooperating (for now).
I decided to go with the buskote stuff mentioned, and liked, by others in the past. Although I'm dubious of their "thermal performance" claims, it's not an unreasonable price for good quality paint and any thermal benefits can just be bonus

I've spent a ridiculous amount of time scraping the bahesus out of the of old paint on there now (4 days!!!). The peeling paint was getting to be really bad, with large spots "bubbled" out all over the roof. It's strange, this is only happening on the roof. The rest of the paint (sides, etc) looks great.
Anyway, my original intent was to "rough up" the paint with a sander with 50 grit sandpaper.
Upon inspection though, I found the paint easily scraped off (in sheets and rolls) using little effort with a paint scrapper. So I've taken to scrapping off as much of <that off as possible (thus the time). It's become a sort of zen chore and it's strangely satisfying when a whole bunch of it just rolls off, lol

As I'm most of the way through the sanding, I've got a nice dull, scraped up layer (sometimes to bare metal, other times to what I believe is original primer(?)).
After sanding is done,I plan on cleaning it with dish soap and water and wiping it down with a rag.
Then I had considered using an acetone wiping step, but am reconsidering that (read reports of it softening old paint and making a real mess).
I'm now looking at a wax and grease remover of some kind.
Then I'll tape and roll their primer
Wait 24 hours(ish) and sand down any bumps
Tape and Paint layer 1
Wait and bake 24 hours (or longer? Days? Weeks???)
Tape and Paint layer 2

Does that seem like a reasonable list?
Anything I'm missing?
Any other suggestions?

Your thoughts are appreciated as always,
George

[scanzel]

Yes acetone and lacquer thinner at times can soften paint and plastics. I would talk to a body shop supplier and see what they have for a final prep cleaner. Make sure there is no silicone residue too as paint will not stick to it. Good prep work is what makes the final job rewarding. Good Luck.

[Oonrahnjay]

...  Your thoughts are appreciated as always, George

    I did the Bus Kote thing -- I had access to a full canopy roof shelter to work under and it came out very well.  I did "their primer", 2 coats, and one of clear; that's what they recommended and I think that all three sections were good for my job.  The NC sun isn't as direct as FL (and maybe SoCal or AZ) but we can get pretty hot in the summer -- I'm convinced that it made a significant improvement in interior heat levels.

[buswarrior]

Don't fall off the roof!

Safety slips out of sight as we are distracted by the job at hand.

happy coaching!
buswarrior

[Dave5Cs]

George sounds good. Question? did you use their pre-mixed paint and Insulating ceramic, or did you just get the ceramic to mix with Elastomeric paint of your own? Will you be used the flex clear over it all?
Looks like its about 500.00 for supplies if you use all their mixes and paints etc. Is that about right?
Dave5Cs

[Jim Eh.]

Don't know if there is oxidization on the bare spots (something had to cause the primer to de-laminate) but that should be addressed. Sanding alone may not be enough. You may have to etch the aluminium to ensure adhesion.

[Geoff]

The roof on my bus was painted 12 years ago with 2 stage paint.  I could tell as soon as I got the bus back from the painter that they really cut corners and put a thin layer of paint and clear coat on the roof, which did not hold up as long as the sides of the bus.  Now I am in the same boat as you-- having to sand and scape the peeling paint.  I am just going to sand and prime, then put a coat of one stage paint.  It should last longer than me.

BTW, if the paint bubbles, it means poor surface preparation.  I also have a few spot on the sides I am having to repaint because of bubbles and peeling clear coat.

--Geoff

[DoubleEagle]

Don't know if there is oxidization on the bare spots (something had to cause the primer to de-laminate) but that should be addressed. Sanding alone may not be enough. You may have to etch the aluminium to ensure adhesion.

If the aluminum is exposed at all it will form an aluminum oxide coating very quickly and will need to be treated with an acid etching compound or painted with zinc chromate primer (if it is still available), epoxy primer, or specialized primer that is acid etching for use on aluminum. The major paint brands have versions of these. Marine supply places may still have zinc chromate in spray cans available. Any paint that you put on aluminum that does not have adequate preparation will eventually fail, as you have seen.

[Geom]

Well, another day of prep/scraping/sanding down, and one more to go 
The scraping is slowing things down since I'm only using a 1" chisel to remove it.
The actual scraping tool I bought pretty much sucked and the chisel is working way better.
But anyway, the best I can hope for now is to get the primer on before it starts raining all of next week.
I don't know how long I can go before applying the paint, after the primer; but it might be a couple of weeks. Or if I get one layer of paint on, how long I can wait before applying a second.

The aluminum wasn't directly exposed before (it is now in spots after sanding). It looked to be peeling down to some smooth grey primer looking stuff. I'm not really going to mess with it any further as far as acid etching, etc. Hopefully the vigorous sanding and cleaning will be enough.

It occurred to me, mid-way (after buying and reading the label on the bottle) that I perhaps should've cleaned first then sanded. Oh well. One half of th bus has already been sanded before I came to this little nugget of knowledge
I did decide to do the wax and grease cleaner over the acetone. Although I might acetone the bare aluminum spots to help pull any possible oxidation(?).

I ended up spending about $380 (with shipping). I bough their premixed paint. I believe they're probably best qualified to balanced the viscosity of the paint with the ceramic insulator stuff for best coverage. It comes as white only, but a place here in town will colorize it for me.
But yeah, all in all I've probably spent about $500 between prep materials and paint, but haven't finalized the full tab yet, lol.
I decided not to do the clear coat on top. I talked with the support gal and she didn't believe that on a roof it'd make that much difference and it might make future touch ups a pain.

Anyway, back on to the roof again today. Hoping to be final cleaning, taping, and priming by this afternoon.

Thanks again everyone for the tips and advice, and yes I've been working very diligently to NOT fall off of the roof, lol.

George

[Cary and Don]

Just picture how nice it's going to look. We need pictures.

Cary

[Geoff]

You have to use an etching primer if you are painting over bare aluminum.

[DoubleEagle]

You have to use an etching primer if you are painting over bare aluminum.

Unavoidably true. Your time and money will be wasted without proper preparation.

[Geom]

Unavoidably true. Your time and money will be wasted without proper preparation.

Even if the aluminum was just now exposed due to my recent sanding?

The primer I'm using says it can be used over several surfaces, including aluminum, but does not specifically state bare. I assume it would clearly state that somewhere, if it is an etching primer?

Hmmm, I had really wanted to use this primer, but if it won't do the job, what would my options be to get done by tomorrow? Should I (can I) pick up an etching primer and use in addition to this one? Or should I look more toward acid etching?

Hmm...

Thanks in advance,
George

[Oonrahnjay]

Even if the aluminum was just now exposed due to my recent sanding?

The primer I'm using says it can be used over several surfaces, including aluminum, but does not specifically state bare. I assume it would clearly state that somewhere, if it is an etching primer?

Hmmm, I had really wanted to use this primer, but if it won't do the job, what would my options be to get done by tomorrow? Should I (can I) pick up an etching primer and use in addition to this one? Or should I look more toward acid etching?

Hmm...

Thanks in advance,
George

     Acid-etching only on the bare aluminum.  There shouldn't be anything (old paint, other primer, etc.) between the etch primer and the aluminum.

[Geom]

     Acid-etching only on the bare aluminum.  There shouldn't be anything (old paint, other primer, etc.) between the etch primer and the aluminum.

Ahh, ok. So I can just hit up the small patches where some aluminum started to show, and then use the original intended primer over the whole roof?