Painting aluminum?

admin

I usually paint steel, I have a good system, epoxy primer, and 2k epoxy finish coat,I know the oxidation on aluminum makes it tough,Should I sand everything with a DA, sander, then wipe with acetone, then paint with epoxy primer?Or should I use etching primer? Is that even necessary?Thanks Sent from my SM-G973U using Tapatalk

http://www.philswelding.com
Reply:

Originally Posted by MetalMan23

I usually paint steel, I have a good system, epoxy primer, and 2k epoxy finish coat,I know the oxidation on aluminum makes it tough,Should I sand everything with a DA, sander, then wipe with acetone, then paint with epoxy primer?Or should I use etching primer? Is that even necessary?Thanks Sent from my SM-G973U using Tapatalk
Reply:I got a lot on steel but not so much on alum.  My guess is someone knows more will come along.  But no matter what maroon Scotchbrite is your best friend. Any contamination seems to migrate on alum and last I paint I follow some instructions but its been a while and now lots of products lots cheaper than the Dupont we use back in the day.   The etching primers tend to grip, alum is so slippery and fine that epox lays on top like a sheet.www.urkafarms.com
Reply:This is just some generalization,,, not really all about this exact thing but synergistic for lack of a better word.  The smoother it is the smoother it paints.  It needs some etch to bite so you scuff it up.  Sandblast is more extreme issue but alum is similar in the sense and amplifided due to the primer used is really thin, it runs off the peak and in to the scratch, not such an extreme issue with heavier coatbgs will fill and cover but etchers being thin really run off so recoat and sand maybe recoaat, sand very fine and lighter than the original scuff.    I have a bit of blast paint experience,,, over some time and get to see lot of the long term.  This is a super big deal on steel too.  I usually degrease pressure wash and sand if i can, I have blast, will do it but if I can simply sand and paint.  No matter how we do a surface in the end the final thing is the purple pad and blow off with air.   Blow up close it it takes it/  I never wash, none of that stuff and etching primers were even used on steel panels with the thinking for rust and its simply tooi ruff after plasting, primer runs in but not on and the peaks poke thru it the day its painted.    When we blast we scuff after the fact and prime/paint and in the case of expensive outdoor equipment, road trucks, fertalizer etc it gets Corlar and Imron Industrial.  I even use it on trucks tractors, its not quite as smooth as the airplane stuff but week later you dont notice it on a work truck if you dont look for it.www.urkafarms.com
Reply:The auto paint stores have this, a good place to get setup sometimes and I like the new economy paint equipment.  It really works good and cheap enuf to upgrade/replace/change without it being gut wrenching.  The last time I used it,,, a long time, I recall it going a long way, I think there is an activator.  I think the stuff in the Nasson can is the same but lotso cheaper.   But I really like to clean for grease before sanding.  My bet there is a zillion boutique preps for this. When I started painting durable finishes there were wash steps with another product or 2 were the rage to use and they really make a mess and I cant see how it can be good, blast and then wash with some water based stuff or even those spec solvents, rinse it around and if you at this point and got grease or wax yet wtf,,,    Final scuff gets anything we absolutely miss and smooths blast work, feel the difference with clean hand, it doesnt take a lot but pass or 2 and this loosens any sand got splattered and stuck on, knocks the spikes and peaks down so they dont poke thru the primer coats.  Blast dust off with hi pressure air and paint.

Attached Images

Last edited by Sberry; 14 Hours Ago at 01:15 PM.www.urkafarms.com
Reply:When I worked for a sign company we used aluminum for almost all sheet metal. Wipe down with acetone or laquer thinner, DA with 180 grit, wipe down again, and then Sherwin Williams " wash primer". Was primer is a 2 part primer, rather thin and basically just a good " fog coat" is needed. Never had issues with paint adhesion.
Reply:Ya, I painted for signs back in the day also and exactly how they did it, wipe, sand coat and color coat.  I forgot about sign suppliers having paint line, duranotic bronze,,, ha is the brown sheet they all use.www.urkafarms.com
Reply:Epoxy primers (generally) have superior adhesion over etch primers. Get a tooth in the metal for the primer to adhere, sand with 80-no finer than 180.Acetone or lacquer thinners are not the best for cleaning, they evaporate too fast before you can wipe off and leave contaminates behind.Get an automotive solvent W&GR (wax & grease remover) either mineral spirit or naphtha based. Wipe on wet and wipe off with clean towels before it dries, change towels as there get loaded up. Sand first then solvent clean.I don't know what epoxy and topcoats you use and whether you spray or brush, but they are likely Ok, it's in the metal prep.Ernie F.
Reply:I do not know modern paints, at one point used good stuff and we are so much more utility now but I believe 2K and the primer are similar to Corlar and Imron.  After a guy does 1 or 2 and can figure out how much he can hang on in a second coat these are so solid and hi hide its a matter of how much thickness for exposure.  I have a couple things I happened to prime in common brown and hang some imron on it and the coat is so good with no failure under that even stained from foliage and weather with cleaning still looks new and with industrial the cost is a bit different have used it on lots of truck aquipment and its so worth it, often still service worthy even decades of salt and abuse, lots of paint still stuck to it where it didnt get chipped.   So much better than that powder coat and one reason never sure how well its really blasted.  I seen a lot of paint outlive powder right next to each other.www.urkafarms.com
Reply:i agree about the solvent being too fast,www.urkafarms.com
Reply:metal man,Depending on the quality of bond you want w the aluminum there are several considerations ; all based on the chemistry and mechanical quality of the surface of the aluminum.  If, for example you're using some 300-400$/gal. marine epoxy series of paints(?) then most would spend the time to get the best bond. If the paint job is just a bracket or rack that will stay indoors- then less effort in surface prep will get a nice coat that will last a long time - inside- out of the weather.In descending order; paint prep on most aluminum alloys are as follows:  The best is a combination of chemical and physical bond- achieved by sand blasting (correct media for blasting) followed by and acid etch- to remove the oxide followed by a water rinse to keep the oxygen away from the now clean aluminum and that followed while wet - with a zinc chromate solution, like Alodyne, creating a chemically bonded chrome oxide to adhere to the underlying aluminum, w/o any interposing aluminum oxide film.  That is followed by a primer and if needed filler primers then top coats where the first primer adheres to the replacement oxide film chemically and then fills in the 'anchor pattern' from the blasting for an additional mechanical bond once that film is hardened- 'kicked-off'.N e x t down the list is;   to do all the above with a 3M (tm) Scothbrite pad, or a sanding pad in the 120 or higher grits to abrade/smooth/scuff the surface - which gives a 'decent' anchor pattern but not as strong as the blasting impact of particles for the mechanical bond.N e x t down the list is to skip the blasting step and rely on strictly chemical bonding and this could be done with the acid etch and rinse and chrome oxide step- or done with a 'self etching' primer- the latter is considered useful but not on a 'yacht' as the adhesion is not as long term and high quality.N e x t in the list is to skip both etching and buffing - so you're working with a surface that has original mill scale and just use the self etching primer then topcoats.  This last is where an indoor paint job will last fairly well but won't last long outdoors.Tail end Charlie is to simply wipe the surface w de-greaser and paint.  if you sand an entire aluminum surface and don't etch- you're only mechanically attaching the paint- not chemically except to aluminum oxide that will lift easily releasing the paint film on top of laying on top of it. The areas left to the air for a few seconds will all have aluminum oxide within the time it takes to run any sander over the surface.A few things to note;  If aluminum is exposed to air it forms a few mills of oxide in about 4 seconds- all alloys of aluminum do this.  That is why if you use acid to etch the rinse water film dilutes the acid, removes the solution and protects from air by leaving the water on the surface and why the zinc chromate solution is applied over the wetted/rinsed surface- to allow the chromium oxide to form instead of aluminum oxide- and there is a color indicator that this bond has formed.  IF there a blue or green patches instead of a uniform gold to brown film on the metal - that area is not converted to the chrome oxide film.Mill scale is not vapor proof, it will in fact hold water vapor against the parent metal and promote 'white flowers' which are the beginning of crevice cell pitting sites.  Acid etching aluminum will remove all mill scale AND aluminum oxide (which won't hold paint well)  if the acid is sufficiently active.  Hot vinegar will actually help remove mill scale but might need to be applied several times to obtain the cleaning action of one single spray of a compound like Zep-a-Lume.Hope this helps with an overall review of common practice in marine aluminum painting- boats and related gear.   I've done this since the late 1970's including all the levels mentioned above and observed the results since that work was done.Just a report from my experience, but I think this is a fair review of the levels of paint prep. although limited to the 5000 and 6000 series of aluminum alloys. cheers,Kevin MorinKenai, AK
Reply:How I would do and how he can do might be different. Limitations on location and equipment.  If I have a choice and looking for the best its spray with industrial purple degreaser and stripper then very deliberately and squarely how hi pressure wash. If its gonna be blasted then its blast, scuff/sand then blow and paint. I found a can of prepsol in a cab a while back, thought wow and grab it, none or gone then figure it to be there since 94 and a hundred jobs ago.www.urkafarms.com
Reply:

Originally Posted by metalman21

Epoxy primers (generally) have superior adhesion over etch primers. Get a tooth in the metal for the primer to adhere, sand with 80-no finer than 180.Acetone or lacquer thinners are not the best for cleaning, they evaporate too fast before you can wipe off and leave contaminates behind.Get an automotive solvent W&GR (wax & grease remover) either mineral spirit or naphtha based. Wipe on wet and wipe off with clean towels before it dries, change towels as there get loaded up. Sand first then solvent clean.I don't know what epoxy and topcoats you use and whether you spray or brush, but they are likely Ok, it's in the metal prep.
Reply:They're aluminum cable rail posts, outside, not near Salt water though.

Sent from my SM-G973U using Tapatalk

http://www.philswelding.com
Reply:I'd like to get them powder coated but I'm under a time crunch, and the powder coater is notoriously late when I need something done fastSo Napa sells an 2 part etching primer, I'm thinking of doing the following:DA sand everythingDegrease with solvent just before painting,Self etch primerEpoxy top coatAny  thoughts? Sent from my SM-G973U using Tapatalk

http://www.philswelding.com
Reply:Kevin, I agree with what you posted. I was going to add info about acid washing (I use Henkel Aero 33), but not without using Alodine immediately after. No doubt it is a very good prep. It just isn't always practical.However I have sprayed a lot of outdoor aluminum fabrications the way I described and they held up very well.  A lot has to do with the quality of the epoxy primer and topcoat paint. I started around 1970 (still do it if I have to

) and seen a lot of products come and go.Ernie F.
Reply:

Originally Posted by MetalMan23

I'd like to get them powder coated but I'm under a time crunch, and the powder coater is notoriously late when I need something done fastSo Napa sells an 2 part etching primer, I'm thinking of doing the following:DA sand everythingDegrease with solvent just before painting,Self etch primerEpoxy top coatAny  thoughts? Sent from my SM-G973U using Tapatalk
Reply:

Originally Posted by metalman21

I'm not familiar with that epoxy primer. Is it activated? The product I use is activated 1:1 and can be top coated without sanding within a few days.I'm inclined to advise skip the etch primer. Most all I've used were nothing more than lacquer with a small amount of acid. Don't misunderstand, I used to use the etch primers years back and didn't really have problems. It's just that the epoxy adheres better and the topcoats are less apt (prone) to chipping.
Reply:PhilI sent you a PMErnie F.