Filling Pits for Powder Coating

leo

leo

Well-known member
I want to prepare some not sheetmetal (steel) parts for powder coating that are quite pitted. I'm told that bondo does not work because the 400 degree bake process for the powder coating frys the bondo. I'm also told that JB Weld will hold up to the 400 degree bake process but some powder coating places will also heat metal to 600 degrees prior to sandblasting to remove any oily contaminants from the surface. I know that the pits can be filled by brazing or lead but I really don't want to go that route if possible. What is the easiest way to do this?
 
Looks like there are no easy answers to this task. Are there any other products which anyone has used?
 
Dave, while I appreciate your compliment, the problem is I don't know how it can be done on a hobbyist level. The Lab Metal needs to be heated and cured ...and in the perfect world needs to be done prior to leveling. If you fail to do this you will see imperfections in the finish.

Another method is to apply the powder and do a partial cure followed by sanding the partially-cured paint to level the pits and then re-apply the powder and do a full cure. Again, having the equipment (oven) at our disposal makes this an easy option for us but not a hobbyist w/o an oven.

Leo, I will also tell you that we/I do not (intentially ;) ) preheat to 600° to remove any contaminants. There are chemicals that are much cheaper to use than the energy necessary to get items to that kind of temps.

JB Weld is not real conductive and as such, powder does not like to statically attract to that area which can create performance issues. Brass & Lead are options but brass can be a little difficult to flow uniformly and tough to metalfinish. Lead has a melting point of around 600° the best I can remember, so you would need to be careful using Lead. Have you consulted with the P/C shop to see what they can recommend and/or offer?
 
What I have learned.

There are two types of lab metal. One needs the full 24 hours or you will get outgassing. The other needs to be oven cured first. Check out their website. Lab metal is kind of interesting to work with, but JB weld may be fine.

I tried the JB weld and it did just fine with my home powder coating using the Tiger Drylac black that Brent had recommended at one time.

You need to discuss with the person doing your powder coating to find out what they will allow you to use.

You can pick an oven out of the trash and buy your own powder coating stuff. Not very hard to get good results. I bought the cheaper Powder and just switched to the more expensive stuff Brent uses. I suggest you spend the extra money. I have one of the cheaper guns and it does waste a lot of powder. The real guns are some real money- not in my budget.

Go to Caswel plating as they have a forum on powder coating and you can see what others have done.

My oven was too small to do wheels so I added a metal box out the back. I have done some longer items like brake cross shafts. The catch is you need to make so odd jigs to hold the parts.
 
Though I'm not an expert in powder coating, couldn't one use a hard solder to fill in holes prior to coating?
 
HI: I never power coated any thing but I've had metal that had pits some really deep and I took a grinder and ground the metal down to where it's smooth again I did this on some old bumpers that I didn't care if I ruined it or not but it was cheap but the time. The funny thing is it came out smooth and level it surprised that it came out like that but it did about fell over but when we had it re-chromed the guy said he didn't have to do a thing to it other then the normal stuff but I seen the bumper not to long ago and it still looks nice. It was on a Model A coupe reggiedog
 
Some of the projects I've been in used the 2X's or 3X's powder coating process ( maybe
4X's...can't remember) with a sanding in between. The parts came out " CHERRY ", BUT
it ain't cheap....
 
Regular JB weld worked perfectly for me. The backing plates, frame and rear axle assembly including tubes and trailing arms were quite rust pitted. I sandblasted everything and coated a million rust pits with regular JB weld then sanded it smooth with a DA orbital sander.
*In regards to JB being non-conductive...TWO different shop and FOUR different people did my powdercoating as I restored the pieces in batches. I know they experimented with preheating some of the smaller pieces which had larger areas of JB weld, but they didn't mention having severe problems, nothing bubbled or lifted and the pieces came back looking great. I think it helps that I sanded the JB weld completely flat so that ONLY the pits were filled and plenty of bare metal was exposed between the pits.
Powdercoat is quite forgiving and doesn't shrink and sink after you get it back (like regular paint)...in fact to the best of my knowledge once it leaves the oven it's cured...period. For this reason the filler can be leveled further, with courser sandpaper even, than in regular bodywork as it isn't going to shrink & leave a ring around each repair. In the event you push the limits and have any bodywork showing through, it can be wetsanded & cut-polished with ease.
*Tip* If you warm up the JB weld & your metal with a hot air gun, it will flow deeper into the pits and spreads like icing.

1)I tried solder and it melted in the powdercoat oven.
2)I also tried bondo and USC all-metal on a sample and it came back slightly blistered. When I dug into this sample with an awl, the bondo and all-metal had been "cooked" and flaked off like soft chalk.
3)I bought a small can of Labmetal from a POR15 vendor, but it sat for about a year (unopened) and was rock hard when I opened it.
4)I didn't experiment with the HIGH TEMP JB weld ... as the regular JB worked excellent.
 
Bob, look at the temp range for that product. Many shops cure at 400 degrees +/-3%. A person that uses it woud need to make sure his P/C shop did not exceed the temp ratings.

Craig, your thoughts about using a Heat Gun may be useful in curing Lab Metal for the home hobbyist. Good tip.
 
Yes Brent thanks, I had seen that. It overlaps with TDs recommendations for their PC materials however, and I believe they are the largest supplier (?). Just offering it as another option.
 
You must log in or register to reply here.
Back
Top