TheSamba.com :: View topic - Epoxy Primer over Filler or Filler over Epoxy Primer?

Thu Mar 13, 2003 8:55 am

I hope someone can help me answer this question...I've bead blasted the body of my 60 type 1 and have welded in some new panels but now I am confused. I notice on other posts that they say to apply the primer over the filler but I've asked some local body shops and they say the opposite? Is it product dependent?
Thanks in advance
Grant

Thu Mar 13, 2003 1:38 pm

Not an expert but already gone through this on my bus.

I like to use USG all metal. Build up thin as it's a bitch to sand. Start with 36 grit to take high spots down quickly then go to the 80/150 etc.

I like to put filler direct to metal. Scuff metal up good for tooth (36 grit will do fine)...then scrub it good with denatured alchohol or acetone to make sure substrate is clean. Then primer/filler/sealer on top of that. Note: Don't use self etching primer on top of filler. The acid used in the etching can loosen or soften many fillers. Use an epoxy based product like Duponts DTM (direct to metal) epoxy. Now you have waterproof and corrosion fighting filler with a durable epoxy barrier coat to make sure the rust never comes back. If you have surface rust spots, sand or wire wheel them to clean metal (or sand blast....plastic media does not remove rust) and then hit with POR 15 (resto motives) Metal Prep to kill the rust you can't see. Follow their directions. Then sand that spot again before priming. You can use several dupont high build filler/primers right on top of the epoxy DTM. the DTM is designed not be sanded. You flat sand the high-build primer prior to your top coat. You can use another coat of sealer prior to top coating but many Dupont high-builds like 4004 and 4900 series have great top coat holdout so you can spray right on top. Use tint of primer closest to your topcoat for better coverage and less product to be sprayed. Good luck.

Doug

Thu Mar 13, 2003 1:39 pm

Clarification: USG all metal is filler like "bondo" in as much as it is designed to fair out imperfections like panel welds, small dings, etc...prior to primer or sealer.
Doug

Thu Mar 13, 2003 5:54 pm

Hey Doug,

Can self etching primer be used on partially painted/bare metal areas prior to mud work?

Thanks

Fri Mar 14, 2003 8:26 pm

Try not to get any etching primer on painted areas. A little over spray is OK but don't over do it.
No plastic filler will work directly on top of etching primer. Use a urethane primer over the etching primer, scuff it up with some 80 grit and apply your filler over that.

Done this way you will have a solid foundation to build up on. The urethane primer should be a high build primer and after your filler work another 3 coats and block sanding in between will be enough

Mon Mar 17, 2003 11:00 pm

59 is right on. I would recommend a courser grit on the rough up though. Grab some 36 grit to quickly put some good tooth into that primer. Don't push hard and overdo it. You don't want to go through the urethane primer. 80 is probably OK but I am always paranoid and want the filler to stick for good. Even though you shouldn't go over 1/8" thick with filler unless you are using a fiberglass reinforced filler like USG's long and strong or duraglass. They are both waterproof and can take a higher build than plastic fillers. You should drill a couple anchor holes if you go over 1/4" but the best thing is to work and/or replace metal to get it to within 1/16" to 1/8" max.

Doug

Wed Mar 19, 2003 6:35 am

I just had this conversation with my body guy. You HAVE to use either self etching or epoxy over bare metal. Nothing else will stick. The catch is, you CANNOT do bodywork over self etching, but can over epoxy. The best plan would be to lay down a few coats of epoxy, then do your bodywork, then your high build. This is what he did on mt 72, and it turned out great. So, I am repeating the preocess on my 78 . hope that helps.

terry

Wed Mar 19, 2003 9:50 am

terry is right..every custom painter i talked with says the same thing..

http://www.extrememetalpaint.com/ these guys are good and say the same...

Wed Mar 19, 2003 2:58 pm

As my first post said, you don't want to put etching primer on top of filler or vice versa. 2 part epoxy is always the best direct to metal bet when your metal work is less than perfect.

I still say with proper prep....putting your filler direct to metal and sealing that with DTM epoxy is better than the opposite. It will also help hide your feather edge prior to the high build. The key is to scratch the metal up well and clean with acetone or another fast flashing solvent to remove any wax, silicone, oil, etc. Most body guys will say it is OK to put your filler on top of primers and sealers that are not self etching but the ones that charge the most do skim coats and slight fills direct to metal prior to initial epoxy spray. It is really up to the person doing the work.

Doug

Thu Mar 20, 2003 10:23 pm

Ok, the question sort of goes out again: Can epoxy primer be used on partially painted as well as bare metal areas? I currently don't want to strip the entire bus to bare metal. I am working with thin original paint & areas that needed to be stripped for repair.

Sat Mar 22, 2003 11:53 pm

Epoxy primer can be sprayed over paint, as long as there is nothing bad under the paint (ie. moister, a little rust etc). Note that though epoxy primer is much more water "proof" than most primers, it is not like pure epoxy resins. Water can seep through it. This is probably not a problem for most VW fans, but where I live it is even wetter than Seattle! So these are the things we are concerned with, but we still use epoxy because it is the best, just don't think that it is completely water proof. (And no I am not just some shmuck who thinks this about epoxy primer, I am a chemist) I have used it on my ghia and it has been on there for 8 months and I have seen no problems with it, even in the areas that it was sprayed over paint. I totally understand not wanting to strip the whole vehical. Just a note about epoxies, the longer they spend to cure the stronger/more water "proof" they will be. After saying that follow the instructions on temperature the paint company says to do it at, they know what they are talking about, if you mess it up you can end up with a primer that never cures.

Skaven Xavier

Mon Mar 24, 2003 7:59 pm

The basic rule of thumb, and what you will read on most paint brands instructions, is it is OK to paint over "properly prepared original factory paint". That is as far as I would dare take it. And I would rather media blast to bare metal. If you aren't putting a super spendy and color sanded paint job on your rig it is fine to paint over mixed substrates and YES, epoxy would be your best bet for that purpose. If you are going to put an extra 100 hours into the final sanding and polishing after top coat, take the extra 5 hours and blast to metal.

Doug