Priming bare aluminum questions

[Charles in SC]

In my Aircraft Spruce catalog Zinc oxide primer is on page 374. Part # 09-00962 for a quart. 09-00960 for a gallon in green.

[Larry B]

I am not a professional paint, but I did paint my own bus with air sprayer and a brand name paint called Endura. It can be mixed in any color you want. It is the same paint used on industrial equipement ( drilling rigs etc.- nothing takes more of a beating than a drilling rig). This is tuff paint and cheaper than auto. paint. This may not be a desirable option to you but most of all I wanted to give you a heads up on aluminum. Aluminum starts to oxidize in about four hours, so from the time you clean the bare aluminum until you get some paint on it should not be any more than four hours. I was told this by two separate body  shops when asking questions same as you are doing now. If you are doing this job by yourself, this will not be possible, but you do not have to paint the whole roof in same day and it does not sound as you are looking for perfection. For cleaning the bare aluminum I used lacquer cleaner. same stuff you clean your spray gun with. I put the cleaner in an old spray bottle (windex) and sprayed the cleaner right on the bare metal. With a rag keep on wiping and reapply cleaner until no more black oily residue is evident. Aluminum is oily be nature of the metal.You are ready to paint. Hope this helps a bit and I am not too late before you paint.
           Larry B

[Iceni John]

Thanks, Larry, for that good advice.   I'll start tomorrow.   Fortunately the roof is in seven sections, each about 5 feet wide, so I can do this in stages.   I'll first sand with 100-grit aluminum oxide paper to roughen the surface and remove the oxide and corrosion on it, and wire-brush (with brass wire wheels) around the rivets where I can't sand, then wipe down with PreClean 191 and microfiber cloths.   Without any delay I'll brush on two thin coats of the Mar-Hyde etching pre-treatment primer, then as soon as it's dried I'll roll on the Rustoleum clean-metal primer over the Mar-Hyde.   Yes, I know that aluminum oxidizes immediately after it's been sanded, thus the hurry to get the etching primer on as soon as possible.   I opened the can of Mar-Hyde this evening to have a look at it  -  boy, does it smell!   It's way too volatile to pour into a paint tray and roll on, so I'll have to brush it instead.

If I can get one section primed in a day I'll be happy.   At that rate it will take me a solid week to prime the whole roof, then I have two or three coats of the white top coat to roll on.   I intend to get it all done by the end of the month, before the first winter rains come.

Charles, yes, I know about the importance of keying the surface for the paint to adhere well.   My thought is that both sanding and using an etch primer should work as well as I can do in the circumstances (outdoors, with expensive RVs either side of me).   Some of the original paint had separated off the roof, presumably from careless or inadequate preparation, hence my desire to not take shortcuts this time.

Wish me luck tomorrow!
John

[tom120]

doing this in sections makes the most sense. it will eliminate dry edges where adhesion could fail. you need to use an etching primer with phosphoric acid or zinc chromate. there are tons of them out there. to my knowledge urethanes etching primers will need to be sanded before color coating. you do not want to have to sand all that surface area. be sure to wear plastic gloves when stripping to keep oils and sweat off the surface. I always finish the sanding with 80 grit paper on a da sander.  it gives you a little extra physical grip along with the chemical grip. an 80 scratch on bare metal is not the same as an 80 grit scratch in paint. avoid polishing the surface with lighter grits. you can wash with a metal prep before etch priming. don't prime in the sun or heat. you don't want the solvent(acid) flashing off before it etches into the top surface. etching primers can be topcoated directly over the etch primer at the prescribed interval. waiting too long will have an adverse effect on paint adhesion. too soon may form solvent popping thru the paint surface. if you pass the interval for topcoating just re etch over top of your existing etched surface. it will bite right back in. remember the primed surface is not a barrier against weather. it needs to be top coated for moisture protection. also best to spray on low humidity days. don't cheat with top coats. at least 3 good medium coats of a urethane paint--no acylic enamels(they craze over time). insufficient paint millage can lead to delamination (peeling)of the paint--esp on a top surface. make sure you get the tech fact sheets with all the products you are buying. the counter guy may not be up to speed on every aspect of every product. the sheets will have everything you need to know and the retailer has them or he can print them online. good luck