Aluminum begins to form an oxide layer immediately on exposure to air, if it's not already present. This is what helps keep corrosion down.

Options:

1) Don't paint it. You don't need to - aluminum won't corrode outside of caustic environments (generally) anyhow.

2) Sand or brush the oxide layer off, wipe it down immediately with mineral spirit or denatured alcohol, and spray down as soon as it's dry with acid-etching primer (and you'll usually end up with an oxide layer anyhow.)

3) Anodise. Anodising is simply a special form of an oxide layer on the surface - it can be made to take a colour (many colours are available,) and you can make the oxide layer harder than the base metal (a MIL-spec hard anno on aluminum that has been mildly knurled will make a part that can be used to literally saw through an aluminum plate. Not sheet - plate!)

4) Powdercoat. Powdercoating isn't as hard as a good hard anno, and it's an applied finish (instead of a surface-layer conversion,) but it's stuck on better than most epoxy finishes.

I'd honestly say that option #3 is your best bet if a specific colour is desired, with #1 or #3 (clear anno) for metal "in the white." Powdercoating aluminum is reasonably effective, but anno is a better option.

Depending on the size of the parts and what means you have available, you can get anno or powdercoating kits to use at home. You can also fully DIY your anno setup with a little research. (Powdercoating requires heat, so you will be limited by the size of the oven you have available.)

Another option - if you need a muted colour - is an interesting PTFE/Moly finish that is available for use with firearms parts. I've seen it through Brownell's, and I've been wanting to get it for my refit to use on certain parts (mainly underbody stuff - brake calipers, backing plates, axle covers, and the like.) The colour selection may have expanded by now, and it's something that may bear looking into, depending on your needs.

 

2) Sand or brush the oxide layer off, wipe it down immediately with mineral spirit or denatured alcohol, and spray down as soon as it's dry with acid-etching primer (and you'll usually end up with an oxide layer anyhow.)

Try using a faster evaporating solvent than mineral spirits, like lacquer thinner... In fact in a non booth, they recommend even letting that sit 15 minutes before painting. Mineral spirits is one of the slowest evaporating solvents out there, and any left on the surface will cause problems when you try to paint over it.

I just did another test piece.

Should i have cleaned with mineral spirits immediately before spraying the primer? I followed the directions and did this

1:Washed thoroughly with mineral spirits
2:Wiped off residue
3:Heavily scuffed the entire piece with scotchbrite
4:Wiped off dust
5rimed ASAP. 3 light coats 2 minutes apart.

How long should i let it dry, before applying paint?

Also, i feel like i should have done another mineral spirit wash after scuffing, should i have?

What process are you using to scruff it? Car paint is much softer than metal so using a gray or red scotchbrite pad is usually good enough. For metal itself, I like to use even more coarse stuff... I don't use metal etch as I prefer epoxy primers (I spray 2k stuff though, not rattlecan). I usually finish bare metal down with 40 grit sandpaper on my DA sander. It doesn't actually leave 40 grit deep scratches as the metal is so hard, but it ususally gives it enough teeth to bite into. Also, any oils on your hands or from not a good thorough cleaning before hand will actually be sanded INTO the metal when you go to scruff it up. I also scruff with my scotchbrite pads or sand paper in a case like this using water with a small amount of dawn dish soap mixed in... This will prevent you're sanding from putting oils and other contaminates into the 'pores' of the metal.

Last, after I got everything set up ready to spray (as in, I wont have to touch the panel again until after its been painted) I'll do a final wipedown using a fast evap solvent, like lacquer thinner.

The best way to wipe things down is to spray it on, or wipe it on with a wet cloth, (cotton is best but make sure what ever you use doesn't leave lint) and then wipe that off with a clean dry cloth.... Without going into too much detail, what is happening here is the solvent is wiped on, and that lifts (solvent will suspend oil and other contaminants, but not break it down) contaminants to the top (they float), and then your dry clean cloth following the wet cloth will pick those up.

I know this sounds like overkill in some aspects, and it is, but this is the best way to make sure your part is cleaned and prepped for paint. By eliminating these variables from your procedure, you will possibly solve your problem or get closer to finding out what is wrong.

What metal etch are you using? It could be that it is weak... Also, your flash time in between layers sounds way too fast, but I'm more used to auto body paints... What could be happening is that your quick flash times aren't allowing enough time for the solvents to evaporate, and your trapping them in between layers... I know you said you waited 3-4 hours after laying down a few coats of primer, but this is something that can and has happened. Last, what is the temperature your spraying at...? Temperature plays a HUGE role in how fast something takes to dry... An example: A couple years ago my Jeep had a thin floor due to rust. I wanted to strengthen it without having to cut it out and weld in a new one, so I laid some fiberglass and resin down on it. This was, for all intensive purposes, outside at 40 degrees, since my garage doesn't have heat. It took over two weeks for that resin to dry, and I could still stick my finger nail deeply into it... This is a very similar scenario to how paint dries at too low of a temperature. Ideally you want a minimum of 60 degrees for paint to dry, whereas 75-85* is easiest to work with (as far as automotive paints go).

Hope I gave you some helpful suggestions.

-Joe

P.S. There are acid etch chemicals you can also use. You spray it on, let it bite into the metal and then wash them off (wearing gloves throughout the whole time!). They work pretty well but they are more of an old fashion way imo to do this. It has kind of evolved from acid etch chemical, to acid etch primer, to epoxy primer. The prior work, but as the products evolve, they save steps and cut down costs and time it takes to get something painted (which = more $ profit).

 

I am really set on painting it black, if i can. Worst case i will leave it natural and polish it...


I just did another test piece.

Should i have cleaned with mineral spirits immediately before spraying the primer? I followed the directions and did this

1:Washed thoroughly with mineral spirits
2:Wiped off residue
3:Heavily scuffed the entire piece with scotchbrite
4:Wiped off dust
5rimed ASAP. 3 light coats 2 minutes apart.


How long should i let it dry, before applying paint?

Also, i feel like i should have done another mineral spirit wash after scuffing, should i have?

 

I am really set on painting it black, if i can. Worst case i will leave it natural and polish it...

I just did another test piece.

Should i have cleaned with mineral spirits immediately before spraying the primer? I followed the directions and did this

1:Washed thoroughly with mineral spirits
2:Wiped off residue
3:Heavily scuffed the entire piece with scotchbrite
4:Wiped off dust
5rimed ASAP. 3 light coats 2 minutes apart.

How long should i let it dry, before applying paint?

Also, i feel like i should have done another mineral spirit wash after scuffing, should i have?

Black? Aluminum? Don't paint - anodise! You can get a regular anno or a MIL hard anno in black without any trouble - it can stay flat, or they can do a gloss anno, or probably even put a clear anno overtop of the black anno to give the glossy colour some "depth."

And I'd forgotten about MS being slow to evapourate - it was the first thing that came to mind, although I tend to use whatever solvent is handy (lacquer thinner, denatured alcohol, mineral spirits, acetone, xylene - Hell, I'd be still using thrichloroethane if you could get the stuff! I was cranky when I finally ran out of carbon tetrachloride for cleaning competition rifle brass...)

 

I've used that bedliner in a can. Good stuff......however you need to give it several days to fully cure before messing with it.

I Painted my grill with the stuff after prepping and priming, then I waited almost a week before I put it back together, now the finish is hard as nails.

good luck

 

my grill
before

after

 

Try using a faster evaporating solvent than mineral spirits, like lacquer thinner... In fact in a non booth, they recommend even letting that sit 15 minutes before painting. Mineral spirits is one of the slowest evaporating solvents out there, and any left on the surface will cause problems when you try to paint over it.

What process are you using to scruff it? Car paint is much softer than metal so using a gray or red scotchbrite pad is usually good enough. For metal itself, I like to use even more coarse stuff... I don't use metal etch as I prefer epoxy primers (I spray 2k stuff though, not rattlecan). I usually finish bare metal down with 40 grit sandpaper on my DA sander. It doesn't actually leave 40 grit deep scratches as the metal is so hard, but it ususally gives it enough teeth to bite into. Also, any oils on your hands or from not a good thorough cleaning before hand will actually be sanded INTO the metal when you go to scruff it up. I also scruff with my scotchbrite pads or sand paper in a case like this using water with a small amount of dawn dish soap mixed in... This will prevent you're sanding from putting oils and other contaminates into the 'pores' of the metal.

Last, after I got everything set up ready to spray (as in, I wont have to touch the panel again until after its been painted) I'll do a final wipedown using a fast evap solvent, like lacquer thinner.

The best way to wipe things down is to spray it on, or wipe it on with a wet cloth, (cotton is best but make sure what ever you use doesn't leave lint) and then wipe that off with a clean dry cloth.... Without going into too much detail, what is happening here is the solvent is wiped on, and that lifts (solvent will suspend oil and other contaminants, but not break it down) contaminants to the top (they float), and then your dry clean cloth following the wet cloth will pick those up.

I know this sounds like overkill in some aspects, and it is, but this is the best way to make sure your part is cleaned and prepped for paint. By eliminating these variables from your procedure, you will possibly solve your problem or get closer to finding out what is wrong.

What metal etch are you using? It could be that it is weak... Also, your flash time in between layers sounds way too fast, but I'm more used to auto body paints... What could be happening is that your quick flash times aren't allowing enough time for the solvents to evaporate, and your trapping them in between layers... I know you said you waited 3-4 hours after laying down a few coats of primer, but this is something that can and has happened. Last, what is the temperature your spraying at...? Temperature plays a HUGE role in how fast something takes to dry... An example: A couple years ago my Jeep had a thin floor due to rust. I wanted to strengthen it without having to cut it out and weld in a new one, so I laid some fiberglass and resin down on it. This was, for all intensive purposes, outside at 40 degrees, since my garage doesn't have heat. It took over two weeks for that resin to dry, and I could still stick my finger nail deeply into it... This is a very similar scenario to how paint dries at too low of a temperature. Ideally you want a minimum of 60 degrees for paint to dry, whereas 75-85* is easiest to work with (as far as automotive paints go).

Hope I gave you some helpful suggestions.

-Joe

P.S. There are acid etch chemicals you can also use. You spray it on, let it bite into the metal and then wash them off (wearing gloves throughout the whole time!). They work pretty well but they are more of an old fashion way imo to do this. It has kind of evolved from acid etch chemical, to acid etch primer, to epoxy primer. The prior work, but as the products evolve, they save steps and cut down costs and time it takes to get something painted (which = more $ profit).

Thank you for the really in depth response but you are referencing things wayyyy out of my league. I am a guy with a can of spraypaint in my garage. I.spray it and bring it inside to dry in normal temperature.

I called rustoleum today and they told me to let it dry for a week before messing with it. It takes at a minimum 72 hours to obtain full hardness.

 

Makes sense, the only bedliners I've dealt with are the 2k style ones (catalyst is mixed into the bedliner) that you'd see if you brought your car to be sprayed by a professional. The 1k ones that are available as roll on or rattle can I've herd take days to dry... What could be happening is the solvents in the bedliner are re-activating the primer because the primer itself is also a 1k style paint (aka possibly not solvent resistant once it dries, just like rustoliums normal paints are) and its losing it's adhesion again. I guess I'm not the best guy to answer your questions, I only know information about how auto body shops paint lol, I've never tried 1k (rattlecan) stuff before, outside of random completely unimportant projects.

 

Black? Aluminum? Don't paint - anodise! You can get a regular anno or a MIL hard anno in black without any trouble - it can stay flat, or they can do a gloss anno, or probably even put a clear anno overtop of the black anno to give the glossy colour some "depth."

And I'd forgotten about MS being slow to evapourate - it was the first thing that came to mind, although I tend to use whatever solvent is handy (lacquer thinner, denatured alcohol, mineral spirits, acetone, xylene - Hell, I'd be still using thrichloroethane if you could get the stuff! I was cranky when I finally ran out of carbon tetrachloride for cleaning competition rifle brass...)

Lol il get it.annodized if you are paying.for it.

 

A glass shop that deals with commercial window and door repairs can sell you a spray product for aluminum that works real well. I've used these products to paint thresholds and replacement parts that were installed raw.

 

Short of anodizing. Look into Alumiprep and Alodine. They make two kinds of Alodine. Alodine 1201 is used extensively in aviation and is a gold color. Alodine 1001 is clear and makes more of a chromish finish. Alumiprep is basically phosphoric acid and etches the aluminum, removing all oxidation and contaminants... the Alodine adds a protective layer to the metal, preventing oxidation. Follow it up with a high quality Zinc Chromate primer and shoot with your paint of choice

 

I think il stick o mineral spirits.for now... if.I need all these solvents im gonna leave it.chrome.