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Applying Clear-Coat to Polished Aluminum


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The frame of the rear window in my convertible is either aluminum or pot-metal.  In preparation for the new canvas top, I sanded and polished to frame until the finish was highly chrome-like.  

 

I decided to clear-coat it to prevent corrosion.  Being a thrifty kind of guy, I bought a can of Premium Decor Clear Gloss spray enamel (contains toluene and acetone).  The next day it gleamed, and I took it (and the car) to the top shop.

 

When I picked the car up a week or so later, my window frame looked awful.  (See photo below) The finish had turned splotchy!   I have no idea what happened, but it happened between the time I left the car and when I picked it up.  I don't blame the top guy, of course.

 

Can anyone offer a suggestion as to what happened?

 

Now I need to fix the problem.  First I need to find the right spray.  Then I have to strip the clear-coat from the frame (which will entail removing the frame and glass from the rear curtain of the top) and remove the bad clear coat (with lacquer thinner or stripper, I guess).  When that's done, I have to either re-spray with a different product, or bite the bullet and take the window frame to a body shop to have it clear-coated (but with what?).  Then, somehow, I have to fit the window back into the opening in the canvas curtain and re-attach it.

 

Or, maybe I'll just leave it on the car, in all its glory, as mute testimony to the wages of thriftiness.

 

Anyway, any suggestions on a good clear-coat and/or refinishing technique would be gratefully received!

 

lo-rez window 2.JPG

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It's the porosity of the die cast material, something is leaching up through the clear paint.  That porosity sometimes causes similar issues if it was chrome plated and not prepared correctly.  I've never had luck in clear over buffed trim, so I stopped doing it years ago.

 

I don't think I cleared mine after buffing, I should look at it to see how it looks after 4 years. I'd bet mine just got dull, and did not notice.

 

50 years ago the H.S. shop metal shop teacher said aluminum hazes over and that thin haze prevents more damage.  Die cast/ aka potmetal is zinc based but has differing amounts of aluminum mixed in.

 

Call the top guy to ask if you will get wrinkles in the rear curtain if you remove it. .

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Hi Jon, hi Frank !

Getting on to 60 years ago,(important time line), I was working on my super cool XK120 MC Jag. I had pulled the cam covers to adjust the valves, and was replacing the intake manifold with one from a 140. I needed to have the manifold bored for a set of 2” SUs I had got. So when I went to the machine shop, I took the cam covers along and had the three pieces buffed to the maximum polish they were capable of. Looked so good that I left the hood off for a while. Impressed the guys at the SCCA races who knew my car well from the days Toby owned and raced it. Lots of pictures were taken of it. Now here is where the time period factors in. Seems to me , but remember, this was a long time ago, that I might have waxed the shiny surface. Honestly, I can not say for sure. But I would NEVER coat aluminum or pot metal with some polymer of dubious adherence, and questionable durability. If it were a product specifically engineered for that purpose, hey ! maybe I would try it out on some disposable piece of similar metal and see how it held up. I think porosity would be another factor which could make wax work. Since my memory is like that of most guys my age, I would have to research in order to find what wax would work best, and then try it on a sample , too. But I think there must be some specific product for this purpose. So many things I wish I could remember from days of old.   -    Carl 

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I don’t know the answer, but I have had problems with aluminum alloys.  Recently thought I would have a part ceramic coated, and the ceramic ended up with pinholes in it.  I wonder if anodizing is the answer.

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There has got to be some kind of contamination on the aluminum.  I also think that the aluminum should have been prepped.  The POR -15 folks have a clear that is made to be used in places like this.  I used some on cast aluminum running board about twelve or thirteen years ago and it worked fine and is till there and looking good.  

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From my experiences with trying to clear coat aluminum is that the clear won’t last. It will start flaking off. It seems to not adhere to the aluminum. Just look at aluminum rims on older trucks and you will see what I mean.             Now when you paint aluminum after a thorough cleaning to remove contaminates the first coat should be self etching primer, the primer, then color, then clear. If you miss the first step of self etching primer, it will start bubbling.  Any scratches or dings that exposes the primer will let moisture in and it will start to bubble. I do know that when it is polished, there are several steps of finer and finer grit compounds are used with the last is a polish which is some type of wax, silicon, or polymer. Paint doesn’t like any of these. That’s why a good cleaning with a good grease and wax remover is needed before painting. I don’t know what the splotches are, but I would suspect it’s a contaminate on the metal that the clear just doesn’t like. This is just my two cents worth. Mike

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An update on a clear for aluminum.  The POR-15 product is called Glisten pc.  It can be brushed or sprayed.  You just need to be sure that the surface has been thoroughly degreased and cleaned with something like acetone.  The product has to have a hardener but is easy to use.

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