Getting the paint to stick to aluminum.

[jhferguson]

So I have painted and sanded my enclosure down and painted it twice with almost the same exact results. You can just about peel the paint off with little effort. The paint I am using is Rust-oleum Automobile Primer (wet sandable) and Rust-oleum Gloss Protective Enamel (Red). Any suggestions on how I can stop the paint from peeling. Thank you for your help.

[Kesh]

how i do it
clean hands with pure soap
clean case with pure soap
wet sand case
clean case with pure soap
rinse very well
air dry
clean case with alcohol
air dry
spray acid etch primer, two coats, 10-15 mins apart
dry over night
spray plasti-kote super paint, maybe 6 or 7 thin coats, 10-15 mins apart
dry over night
attach decals
dry overnight
spray plasti-kote clear kote, maybe 6 or 7 thin coats, 10-15 mins apart

[LucifersTrip]

maybe the primer is not the best selection or is old, or you're not painting in the proper conditions (ie, I can't paint on a cold winter or humid day)?

I've had very good results using the self-etching primer:
http://www.rustoleum.com/CBGProduct.asp?pid=397

[totes]

It probably sounds basic but check if that primer is recommended for use on aluminum. Steel responds to primer differently than aluminum, such that aluminum usually requires more prep to hold paint as well. I know most people recommend powder coating for paint, and it is indeed the most consistent and durable solution, but it is more expensive and requires more effort than just spray painting. I use the rust-oleum Multi-surface primer+paint after light sanding and cleaning of the surface and it turns out just fine if you don't rush the painting process.

[chromesphere]

I used to use an etch primer when i enamel painted my enclosures (i powdercoat these days).  I gave the etch a light sand before the first painted coat.  Pretty sure i used to sand in between coats as well.  I also found baking in a toaster oven for 20-30 mins on about 60-70 degrees C helped harden the paint and also made the process much faster.
Paul

[deadastronaut]

sand it with a course grade wet n dry...180, to 'key' the surface, and to get any grease off...

clean/dry

prime...

wet sand with 600-800....even 1200..

clean/dry

colour...thin coat...dry...thin coat...dry....full coat.

keep box warm..

[jhferguson]

maybe the primer is not the best selection or is old, or you're not painting in the proper conditions (ie, I can't paint on a cold winter or humid day)?

I've had very good results using the self-etching primer:
http://www.rustoleum.com/CBGProduct.asp?pid=397

I don't know much about paint but I figued that Rust-oleum is a trusted name brand. And I just bought it for this specific project so as of today it is like 3 days old (doesn't count shelf life though so not sure about the actual age) and as far as conditions go I have been painting inside of my bathroom because it has a good vent and I can lay down newspaper in the shower so that paint doesn't get everywhere. So 70 degrees, warm and dry.

[jhferguson]

It probably sounds basic but check if that primer is recommended for use on aluminum. Steel responds to primer differently than aluminum, such that aluminum usually requires more prep to hold paint as well. I know most people recommend powder coating for paint, and it is indeed the most consistent and durable solution, but it is more expensive and requires more effort than just spray painting. I use the rust-oleum Multi-surface primer+paint after light sanding and cleaning of the surface and it turns out just fine if you don't rush the painting process.

I haven't checked thouroughly but I know it says "for use on metal" lol. So you only sand your pedals and then use the paint and primer all in one? You don't have to use etching primer or the chemicals that stop the corrosion before you prime? I have heard both of those on several different websites a whole lot.

[GGBB]

Are both the paint and primer coming off right down to the bare aluminum or is just the paint coming off the primer?

I haven't used Rustoleum, but I have used Valspar and Krylon, in both cases using matching paint and primer.  I have no troubles with paint coming off.  I sand, clean with acetone, prime about three coats, sand smooth, clean with dish soap and water, dry, then paint three coats or more sanding lightly and cleaning with dish soap and water and then recoating until smooth.  Then clearcoat using the same process as paint.  Paint and primer need to be well shaken and warm, and surface must be clean, dry and warm.  Air temperature must also be within the recommendations on the can.  Also make sure you follow the recoat time very carefully - if you recoat or paint over primer when the previous coat is past the recoat time and not fully cured, you risk pulling it up with the new coat.  This usually looks bad so normally it would be easy to spot.

[jhferguson]

Are both the paint and primer coming off right down to the bare aluminum or is just the paint coming off the primer?

I haven't used Rustoleum, but I have used Valspar and Krylon, in both cases using matching paint and primer.  I have no troubles with paint coming off.  I sand, clean with acetone, prime about three coats, sand smooth, clean with dish soap and water, dry, then paint three coats or more sanding lightly and cleaning with dish soap and water and then recoating until smooth.  Then clearcoat using the same process as paint.  Paint and primer need to be well shaken and warm, and surface must be clean, dry and warm.  Air temperature must also be within the recommendations on the can.  Also make sure you follow the recoat time very carefully - if you recoat or paint over primer when the previous coat is past the recoat time and not fully cured, you risk pulling it up with the new coat.  This usually looks bad so normally it would be easy to spot.

The paint peels off the easiest. The primer takes more of a light scratch to remove it. But yes they both come off. I have washed it but I may have let it set for too long and also handled it before trying to prime and paint. So after I wash the enclosure with soap and water I need to then use acetone? I read on one forum where someone suggested vinegar. Would that work as well? Also, there has been no thyme or reason to my timing and that may be the problem. I notice that the primer looks good and the 1st coat of paint looks good but the second coat of paint is what messes things up and makes my enclosure look like a dried up lake or something. Incidentally, it could be a nice effect if done properly but I am not on that level.

[GGBB]

I notice that the primer looks good and the 1st coat of paint looks good but the second coat of paint is what messes things up and makes my enclosure look like a dried up lake or something.

Two things usually cause that - either painting incompatible materials over one another (e.g. lacquer over enamel), or recoating after the recoat window (usually an hour or so) and before the cure period (a day or two).

I only acetone after sanding the bare aluminum.  I only clean the primer, paint, and clear coats with soap and water because anything solvent based or otherwise harsh can dissolve, soften, or lift the finish.  I have tried using acetone, isopropyl alcohol, and methyl hydrate to clean the sanded paint or primer and if you use very little, rub very lightly, and work very fast, you will be okay.  But dish soap and water works as well or better and doesn't require that kind of caution so I can do a more thorough job.  I never sand, clean, or even touch the surface until it is safely past the recommended cure time which is typically 24 hours.  I'm not saying my finishes are great or anything - they are decent but I could learn to be more careful and patient - but I don't have problems with the finish coming off easily.

[PRR]

> look like a dried up lake

"Crackle finish". Used to be popular. Does require very specific chemistry to stay-on and stay-crackled for 70 years.

As Gord says: this is the top-coat dissolving the undercoat.

Aluminum has to be CLEAN. Finger-grease may be the #2 worst contaminant.

Scuffing before CLEANing may be helpful, but should not be essential.

Aluminum for household objects, if clean, probably does NOT need a primer. Aluminum "rust" is a lovely thin coat of tough oxide which resists further attack. This is different from "automotive" steel which favors an anodic coating (or body-repair where you need a cheap bulky coat to hide imperfections). And your pedal probably won't drive salty roads all winter.

You can probably use just the one can, Rust-oleum Gloss Protective Enamel should be fine. READ the re-coat instructions.

Painting: Shake can vigorously for one minute after mixing ball begins to rattle. ..Shake often during use. Hold can upright 10-16" from surface and spray in a steady back-and-forth motion, slightly overlapping each stroke. Keep the can the same distance from the surface. Keep the can in motion while spraying. Apply 2 or more light coats a few minutes apart.

Dry & Recoat Times based on 70°F (21°C) – 50% relative humidity. Allow more time at cooler temperatures. Dries to touch in 2-4 hours, to handle in 5-9 hours and fully dry in 24 hours. Primers may be top coated immediately. Apply a second coat or Clear coat within 1 hour or after 48 hours. Apply Clear in 2-3 light coats a few minutes apart.

http://www.rustoleum.com/cbgimages/documents/xxxxxx_0711_SRT_12oz_ProtectiveEnamel_Gloss_f.pdf

i.e.- you can re-coat while still fully soft, *OR* after TOTALLY dry (not just feels dry). If you re-coat when partially dry, the fresh solvent attacks the partly-cured coat and makes trouble.

[seedlings]

i.e.- you can re-coat while still fully soft, *OR* after TOTALLY dry (not just feels dry). If you re-coat when partially dry, the fresh solvent attacks the partly-cured coat and makes trouble.

^ This. 

Light coat, wait couple of minutes, light coat, wait couple of minutes ... repeat as necessary.  If you have to step away for more than 15 minutes, then don't come back for 24 hours.  Not 8 hours or 11 hours, but 24 hours.

CHAD

[R.G.]

II notice that the primer looks good and the 1st coat of paint looks good but the second coat of paint is what messes things up and makes my enclosure look like a dried up lake or something. Incidentally, it could be a nice effect if done properly but I am not on that level.

I like it. From Geofex:




As noted, this happens when a top coat partly dissolves an undercoat. I spent some time with spray cans finding the right combination of undercoat and top coat to get those. In general, the top coat to use is a clear lacquer, the undercoat is not, as lacquer thinner is mean, nasty stuff.

A car-fanatic buddy of mine told me to stop using acetone to clean surfaces for painting. He thinks is always leaves a trace coating of oils. He prefers lacquer thinner, saying it removes much more oil and doesn't leave a thin coat - which sounds like some of the problems described earlier. TSP is good, I understand.

In all cases go get some nitryl disposable gloves. None of this is good for your skin.

[PRR]

> don't come back for 24 hours

That particular can says 48 hours.

Seems long to me, but I figure they done testing and have a reason to make you wait days.

A lot of the old-school rules are changing as they re-formulate paints for VOC and other environmental sins.

Here, it looks like they have two solvents. One flashes-off in an hour. The other is still coming-out in the 24-48 hour period. (Maybe the VOC test only runs 12 or 24 hours, and they put in slow volatiles to fool the testing?)

[deadastronaut]

dry lake bed effect:

that happens if you mix cellulose with synthetic paints. (painting over one another)..it doesn't like it.

[jymaze]

I had similar problems when i painted my first enclosures and here is my solution to avoid that "dried lake effect": THIN COATS.

After the primer, the first 2 or 3 coats of color should only be something like a fine mist, even if the paint looks a little rough or bumpy. It is called a "dust coat'". You make 2 or 3 coats like that at 10 minutes interval (they dry very quickly, almost instantaneous). So when these coats are dry enough (I wait several hours to be sure), the subsequent coat can be a little heavier, but not too much, just enough to have a smooth finish.

[petey twofinger]

ot but , the problem i have is the paint cracking and chipping around the screw holes on the back plate .

[davent]

^I always use black, rubberized  rockerpanel paint for the backplates so no such problems (out of sight out of mind anyways). I'm thinking Hammond enclosures with a beveled recess for the backplate screws here, so you might try just masking off the recesses so they remain paint-free or remove that bit of paint before tightening a screw down into the recess.

dave

[jhferguson]

Thank you all for the replies. I believe that I was waiting too long/not long enough before putting a 2nd coat on. I just primed, waited an hour or so, painted, and then applied a 2nd coat when I woke up. So far it has been much better with all of your advice. I sanded it down (again), washed it with soap and water and let it air dry, applied some vinegar to help with the oxidizing and then applied 2 coats of self-etching primer. After 15 minutes I wet sanded, washed with soap and water again, let it air dry and applied another 2 coats. It has been 2 hours now and I am about to try the first coat of paint. Like I said before so far so good thanks again!