Powder Coating?????
Blackace, I'm really glad you asked because, as you said, not everyone is familiar with the processes involved and there's no such thing as "too much information" regardless of the subject matter. I have to assume your part(s) has some cosmetic issue you want to fix before getting it coated.
Though body fillers are decent for skim coating the outside of your car for a perfect finish, they WILL NOT WORK under powder coating. I have addressed a term called "out gassing" on numerous occasions (usually in reference to pot metal and old used aluminum parts like an intake manifold). It can be either a noun or a verb depending on the context. Basically, it's what can happen when air bubbles and/or impurities get heated up when your part is getting powder coated.
Most everyone on this board has used plastic body filler at one time or another and knows how hard it is to get all those itty bitty air bubbles out. We all remember from science class that heated air expands and rises to the point of least resistance. Keeping that in mind, I'm going to compare plastic body filler with pot metal because the same thing can happen to both.
Without trying to violate any confidences, this is a copy/paste of an email I sent out earlier this week that will help illustrate out gassing. It's long, but necessary to understand what happens. (Ya'll already know I don't just answer questions. I tell you WHY too. :-D)
]"J***, as you may already know, the bezels and grilles on your 64 Galaxie are probably made out of pot metal. Sometimes pot metal can be coated and sometimes it cannot. Results are impossible to predict, and honestly sometimes it works and sometimes it doesn't.
The problem with it is that it's comprised of lots of different types of metal (usually the left over crap LOL) all melted down into one, and then formed into a particular part. With all those different metals melted together, the result is a lot of impurities and air trapped within the part when it's formed.
During the preparatory process of powder coating, the part has to be heated up to a rather high temperature. Most of those impurities and trapped air are usually brought to the surface at that time so they create no additional problems. But sometimes all of it isn't removed no matter how hot you get it, and when the powder goes on and the part gets heated up to cure the powder, the leftover air and impurities come to the surface again. This is called "out gassing." The end result is that your part can look like it has a bunch of little teeny volcanoes on the surface. Sometimes there will be one or two and they won't be overly noticeable, but sometimes it will pretty much cover the entire part. It can also be so extreme at times that you can feel them when you run your hand over the finished part.
I've had both really great and really bad results when working with pot metal, and most coaters won't touch it with a ten-foot pole because of its unpredictability. You just never know what's going to happen until you try.
Some eras of pot metal are better than others (i.e., during war times, all the best metal goes towards ammunitions, tanks, etc., and the auto makers get stuck with the left overs). I can report that I've had fairly good luck when working with pot metal from the 60s and 70s (check out the Mustang and Six Pack emblems on my website gallery, and the Road Runner horn ring coated in Alien Silver for examples), but you still need to be fully aware of the possibility of outgassing before sending your grilles and bezels out to be coated. Assuming your parts will fit in my oven, I'd be happy to try but unfortunately couldn't offer any guarantees of fabulous results.
I know this isn't what you wanted to hear. But unlike some other shops, I'm not going to pull your lariat and tell you "Oh yes send it! I'll fix it!" when the very real potential exists for less-than-desireable results. (Guess I'm one of those rare ladies out there who's honest and isn't just after your wallet. :-D)
If you do want me to give it a shot -- after all, it's a 50/50 chance that it will work and they'll look good -- please forward a photo or two of your parts, as well as measurements (since I'm working with a smaller sized oven at the moment) when you get the chance and I'll get back to you with a quote. If you decide to send them to a "real" chrome shop to get them redone, I'd recommend my buddy Darrell at ChromeMasters in Nashville -- he does great work.
Thank you very much for your email and for the opportunity to earn your business. Don't hesitate to give me a call if you have any questions or want to discuss this further. And I'd enjoy seeing a photo of your baby too -- we just love our car **** around here. Thanks again!"
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In a nutshell, the same thing can and will happen if you try to powder coat over body filler. Even though both Bondo and powders are essentially made out of plastic, the heat's just too much for the filler and it will either blow up into a crater field and/or just fall out of the repaired area altogether.
But there's still some good news amidst all of this for your less-than-pristine car parts.
Permatex makes this awesome high temp metal filler -- called uhhhhhhh "High Temp Metal Filler" LOL -- that was originally formulated for exhaust leaks and is marketed to be good to 2000 degrees. It's a single stage (no mixing!), extremely easy to work with (though admittedly takes some practice to get all the little bubbles out just like Bondo), sets up fast, can be baked, and has proved to be pretty effective on some repairs I've done on customers' parts.
It is kind of expensive though, about $20 shipped for a little blister tube. Compared to the other fillers out there I've tried that were designed specifically for use under powder coating (like Lab Metal, Thermobond-3, etc. which suck in my opinion), I'll stick with my Permatex. Best price I've found is from Caswell Plating since I can't find or order it locally.
PERMATEX® Hi Temp. Metal Repair Compound ... Makes long-lasting repairs to high-temp, low pressure exhaust leaks from the exhaust manifold to the muffler. Gets stronger with heat up to 2000°F. One part, water-based ceramic is safe and easy to use. Suggested Applications: Cracked and broken exhaust manifolds, headers, furnaces. Product No. 26346
Just like with Bondo, it works best when used in several thin layers and allowed to set up in between than one thick one. It might still have a bit of outgassing but it's better looking than that half-inch long crack you were trying to repair. :-)
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Yes, the cleaner your parts are when they arrive here, the cheaper your bill will be. There's a lot of info on my website's Pricing & Shipping page [ http://phoenixs.dot5hosting.com/page4.html ] about this too. The prices listed DO include basic media blasting and a bunch of other services, but are ballpark guidelines since every job is quoted individually. (BronxMopars will recognize his ultra-spotless Cal Customs in my clean parts vs. dirty parts example photo and the bracket owner will remain safely anonymous. :-D)
