VCCA Home Forums TECHNICAL - GENERAL Body - Sheet Metal, Paint & Wood Body filler....

OK....so the age old question. Filler straight on to sheet metal or epoxy primer between the two? Or does the type of filler change your answer? If so I'm using duraglas right now.

The mantra that was pounded into me in body & fender trade school was to put it on bare metal only. The reasoning is putting anything between the metal and the filler is only adding one more possibility of failure. The filler could stick to the primer well but if the primer fails the filler comes off with it.

Tiny, the body filler over bare metal or over primer may be an old subject and very debateable but technology has improved in the last decade or so. In the days of laquer primer I agree it was best to fill over bare metal after derusting and passifying the surface with a light acid treatment( I have used 10% phosphoric acid sprayed on with a squirt bottle and spread with a blue wipe). However, the body shop pro's today rely on two applications of epoxy primer followed by 'roughup' with purple Scothbrite then filler and more epoxy after sanding. It's alot more work, yet i'm convinced you get a better more lasting finish (hard for me to admit it since I'm really old school!) The source who got me to try it initially was Larry Lyles, the Amarillo, Tx restoration shop guy who writes feature articles for Auto Restoration magazine. He has been expousing this method for many years with believeable data to back him up. I was educated as a chemist and often worked with epoxy coatings in the industry so I could see the advantages.
BUT, like all modern two stage reactable materials you better use full body covering and a high grade respirator or fresh air supply when applying. Alot of unwise body shop or hobbiest's have major health problems from neglecting that!
Anyway, I have done it both ways and prefer modern technology. ON the other hand I like the look of enamel topcoats so still use 'em. Thanks for listening.
DFC

The first thing to do is to remove the dent as close to the original surface as possible. If you are using chopped glass strand material to fill imperfections then your initial body work needs some serious attention.
On clean bare metal properly prepared, you can directly apply "All Metal" and glass strand resin type fillers. Sand out and then epoxy primer.
Over the expoxy use the "Bondo" type filler. Block out and prime with epoxy primer. This method will provide the longest lasting type of repairs I have found.

I am with DFC,
I straighten it up as much as possible, clean with acid and then epoxy the repaired section (whole body if a total repaint.

Epoxy has a better chance of staying on the metal. It also keeps moisture, from a chip in the final finish, from working under the bondo.

Then spray epoxy over the finished repair before lacquer primer.

I used to guarantee all of my body work for one year (even rust repair) and in all those years had only one job come back, for warranty,

My body guy thinks like Coley. I had stripped all my sheet metal and then sprayed it with self-etching primer. I thought he would stip only the areas where body filler would be required. He made me restrip everything and give him the parts in bare metal. He then applies epoxy primer on the bare metal, then the filler, some of it the new sprayable type, then sand, sand, sand, buid up primer, then sand some more. Then if required scratch filler then sand again then paint. Or something like that.

My body repair guy recommends the same epoxy primer first method.

He explains that the most common reason for a repair failure is moisture migrating under the repair material. He says that it is critical to "sandwich" the filler in between two layers of epoxy.

I must stress that I ain't a painters backside, just passing on what was explained to me when I enquired.