Painting the aluminum top plate

mingles

New member
I'm frustrated. I've been trying to paint the top plate of my Crack for the past few weeks. The paint I'm using is Krylon gloss red. I think it's epoxy-based. Really nasty toxic stuff. The project started out good. I sanded the plate with 220 grit and wiped the surface clean with rubbing alcohol. It looked perfect. I set up a 2'x'2' box to paint inside. I figured it would keep the dust out and contain the spray. I had a fan blowing out the window about 6 feet from the box. Another window was open on the other side of the room for ventilation.

I propped the plate on 1x4s to keep it from sitting on the floor. I shook the can for 2 minutes and sprayed with gentle even sweeps. I let it dry for 15 minutes. The coat was thin, but looked even. I turned the plate around and gave it another sweep. 15 minutes later, it looked great and was fully covered, but I was determined to give it a thick coat, so I gave it another sweep. This time dust settled in a few places near the front. It was very noticeable. I debated living with it because everything else looked so good. Two days later I used some fine steel wool to rub out the imperfections. I went over the whole top to make sure it was smooth. I'm a hopeless perfectionist!! I wiped it clean with rubbing alcohol and let it dry. I made sure the spray box was dust-free by wiping it down with a wet towel. Everything looked good. Ready for launch. I shook the can and gave the plate some gentle sweeps, but I think I put on a little too much. I came back 30 minutes later and found some of the paint crinkled in a funky way -- like ridges. The temperature was a bit colder this day... maybe 45-50 degrees. A few days later I tried sanding them down, but they weren't going away easily. I gave it another spray and the ridges came back more prominently. I couldn't think of any way to salvage it at this point, so I let it sit for a few weeks.

When the motivation hit, I used a belt sander to remove the paint... down to bare aluminum.

For my second attempt, I did my best to keep the paint area clean. I wiped down the box. I wiped down the plate. The temperature was perfect at 65 degrees. I sprayed with gentle sweeps and made sure not to put too much on. I waited 20 minutes between coats. The can says 10 minute drying time. After the third coat, a weird moire pattern appeared in a few places. I buffed them out with steel wool, cleaned the surface, and gave it another light coat. The moire came back! What am I doing wrong?! This is so frustrating! A few years ago, I painted my Seduction without any of these problems -- same paint, same method. I don't know what's going wrong this time.

I suppose this is a rant more than anything. I'm giving up. I can't stand the fumes or the frustration of not moving forward. I'm going to look for an auto body shop to see if they'll paint it. I can't imagine it costing that much. If you have recommendations for places to have this done, please let me know.

Thanks for listening!

Mark
 
I had problems with my Crack top plate too. This was the first time I had decided to go for a paint finish rather than get the top plate anodised. In my case I tried several different undercoats which claimed to be suitable for aluminum alloys. I finished up with a spray "etch primer". I tested these on a scrap sheet of alloy before I even started with the top plate. The worst of the primers I tried left a coat of paint which could be lifted with a thumbnail.

The finish coat was spray hammer-finish copper. I did my usual (potentially dangerous) trick of three kettles of boiling water in a plastic bucket (in a far corner of the garden) then drop the spray can in to heat for ten minutes. Always seems to give a good finish but you need thick rubber gloves to handle the hot paint tin.

I accept no responsibility for injuries caused by exploding paint cans - I am just saying what works for me (have painted this way for over 20 years and haven't had one pop yet but I suppose there's always a first time...).
 
mingles said:
... The coat was thin, but looked even. I turned the plate around and gave it another sweep. 15 minutes later, it looked great and was fully covered, but I was determined to give it a thick coat, so I gave it another sweep. ...

Ahhhh, Mark... the agony of anal retentiveness... I know it well, personally.  With the Krylon stuff, anything that resembles a heavy coat will ripple immediately.  If you want to build the finish to a heavy coat, you'll need to apply a dozen thin coats.  It's a chemistry issue, and I've actually seen ripples/moire pattern form when I give a surface just a bit more paint...  that being said, when properly applied, the Krylon paints have excellent durability.  I shot the transformer end bell on my Crack amp with satin black Krylon, and it looks like it was powder coated.

That being said... have you considered using a primer, first?  As Fred mentions, an etching primer like Rust-oleum #249322 will help adhesion.

Your final comment about the body shop - yep, that'll work, and they'll generally do it for a pittance.  My wife and I, in leaner days, had a refrigerator repainted twice at a local body shop - and it stood in three different kitchens over 25 years.

Cheers,

-Don
 
When I did the Crack top plate, it was Krylon Hammered Finish straight onto freshly sanded aluminium. The Hammered Finish is a VERY sticky paint, and it came up a treat with four light coats.

But yes, an etch primer first can certainly prepare things for a better finish.
 
Whenever I needed an aluminium top plate painted, I had it done at an automotive paint shop, and had them "VINyL WASH" the metal first, Then finish with an automotive base coat clear coat. I insisted that the top plate should come out like a sheet of glass. For me, that's the only way to go.

Bernie.
 
Thanks for the suggestions and comments. I thought I could get this right with one or two attempts, but I'm gonna bail out. I don't want to be exposed to any more toxic chemicals. Have you ever read the label on the Krylon can? I should have my head examined!! I've been spraying this in my apartment. I set up good ventilation, but it still takes a day or two for the fumes to completely disappear. I don't have a garage or workspace. It's insane to spray this stuff where you live.

Bernie, thank you for this advice:

> I had it done at an automotive paint shop, and had
> them "VINyL WASH" the metal first, Then finish
> with an automotive base coat clear coat.

I want the top plate to look perfect. The Crack will be on a table next to my listening chair. I've always had a thing for Cary's Jaguar Red top plate:

http://www.upscaleaudio.com/media/catalog/product/cache/1/thumbnail/9df78eab33525d08d6e5fb8d27136e95/s/l/slp98.jpg

I'm planning to build a custom base out of Zebra wood. I think a gloss red top will be a nice compliment.

In any case, thanks for the moral support!
 
This guys says Krylon has a piquant finish and should be enjoyed... well, he can't remember the rest ...
0721051gold1.jpg
 
All this red!  I love it.

So far, the only project I have in the works that doesn't have some red on it is my stereomour -- that will be highly spalted birch with walnut trim and recently got the top plate back from the chrome shop with a mirror-like show chrome finish.  The rest of the trimmings on that one will be black and gold exclusively.

Mark, please don't spray that stuff in your apartment anymore -- that's crazy man.

-- Jim


 
I like the HammerTone look, but for colored surfaces on metal I use 1 of 2 techniques for my guitar effects pedal boxes.

1) Lightly sand surface (steel wool works great), give it a few coats of your paint (it should not be too cold), then once the paint has set at least 48 hours I hit it with a few coats of lacquer (warning: polyurethane will yellow with time). Krylon makes a good lacquer for metal surfaces that's cheap in price. Let it sit for a couple of weeks (you could try a week, but if you live in a humid area then you may be disappointed with the results,) and then you can start the polishing process.

2) Use the same as above, only I bought a toaster oven and put my pieces in there for 60-120 minutes with the setting on low-med or 200 degrees. Just make sure you never use the oven for food in the future. This technique works well and gives you a baked-on paint surface. You still need to let the paint cure completely before polishing and this can take a few days depending on the humidity.
 
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