Projects When to apply body filler?

Anthony you snuck in on me. LOL. Lippy

 

The old rule was apply filler only over bare metal. Any old paint must be ground off and feather edged. Grinding roughens the surface and gives the filler something to bite onto. After finishing and sanding the filler, primer and paint.

The epoxy primer came out and it was ok to apply filler over epoxy primer where it is NOT ok to apply it over lacquer primer or old paint.

I have to say, I have seen work done where they weren't too careful about removing all the paint or primer and it did not cause a problem.

The other rule is weld seams must be CLEAN no flux and no slag and no pin holes. Get down with a shop light and your nose almost against the metal and make sure, pin holes will allow moisture to penetrate from the back and lift the filler. Brazing flux will draw water from the air and puff up like popcorn. This is where the myth began that you can't put filler over a brazed joint. Bullshit, all old time bodymen and customizers brazed including the factory. Yes I have seen brazed joints from the factory, with lead fill over them.

So there you are more long lost customizing secrets of the ancients revealed.

 

Body shop teacher I use to work with stressed the three P's.
Piss Poor Preparation means Piss Poor Paint.

 

The filler is porous like a sponge and a really dense air filter.
Metal sweats with temperature change.
So depending on what part of the country what time of the year, shop conditions and what stage you’re at in the body work it’s not really to difficult to get rust started behind the filler. And also depending on the exact same circumstances it’s pretty difficult to get rust started behind the filler,,,, depending.

 

I have found rust under filler and lead.
But let’s look at the causes.
Lead was often applied over a spot welded seam. Not s solid joint. The heat from the process plus time allowed moisture to get under it.
I have seen a lot of lacquer primer wet sanded, even seen filler itself wet sanded in production shops to skip priming steps.
Lots of ways to cause future issues.

 

Same here, though after filler I'll hit any exposed metal with self etching primer, then hi build primer and block sand, finish with a primer sealer before spraying color.

 

Metal rust thru from the back and bubbles the paint/ filler. Got it right now on a race car from the Bonneville salt flats. Also trapped salt and moisture between 2 layers of metal and rusts the top layer behind the paint and filler.

 

I have wet sanded a TON of lacquer primer back in the day. LOL. Never gave it a second thought. I noticed someone here uses 3M green spot putty. I didn't think that stuff still existed. Lippy

 

Oh Jimmy the Metal rusted through from the backside!!!!!! Jeez. On a racecar that would be automatic acid dipped. LOL. Lippy

 

The best argument for epoxy, my own worthless opinion, is on bare metal cars.
Unless you handle the car with gloves and you have a shop with very low humidity, it’s gonna rust during the repair.
Epoxy on a fresh blasted/stripped car saves a lot of extra sanding and work used to remove rust that forms during the work.
Newer higher end fillers adhere to coatings and smaller grit scratches than older or cheaper fillers.
I was taught grind with 36 grit to bare metal then apply filler. Now I’m teaching DA existing factory paint with 80 grit then apply filler.
Both methods are covered.

 

Same here. A painter friend told me he was taught this was a no no due to lacquer being porous. I later learned he was correct. Same applies to many thicker primers like some polyesters.
I always read the tech sheets now.

 

Back in the old days we used DP-40(now DP-90?) over fresh stripped and bodyworked corvettes. Waited 30 minutes and nailed it with three or four primer coats while the DP was tacky. Let her sit for a week or so then get after it. Course back then you had to figure out your own concoctions sometimes. LOL. Lippy

 

I believe the old red and green spot putty were ok to use as intended as the poster is using it here. For little pinholes. But I knew some guys who attempted to use it thicker in gouges in filler and primer and it would shrink up and look like hell later. But used as intended it was pretty good for then. Lippy

 

We used it between coats of lacquer primer. 3 coats then sand. Apply lacquer putty to scratches and pinholes left. Then prime again.
That crap takes a long time to dry in thick coats. And dries top down. Used to hate that stuff.

 

Didn't mean to hi-jack this thread. I get carried away at times.

 

When I worked in a shop that built higher end show cars, I asked the body guy why he used so much filler, when the metal work seemed really straight. He said that a skim coat of filler is a more reliable surface than a heavy coat of high build primer. Its definitely not a time saver, well compared to metal finishing, it is. Most of the applied product ends up on the floor. They also believe that each layer should be a continuous surface, with no break throughs (coat of filler with no metal poking through followed by coat of primer with no filler poking through). I guess that is to eliminate future problems with shrinking of feather edges.

I've tried doing it this way, but I keep going back to just using filler in the problem areas and finishing with high build primer. I guess my standards just aren't that high. One advantage to skim coating with filler is you have better control of where the product is applied. I had a rock chip in a 3 window door hinge that was nearly 1/8" deep because I kept priming and blocking the door and didn't realize how much material had built up on the hinges.

Dave

 

Back to the regular scheduled program.
You can do it either way.
Here are a few suggestions for epoxy.
Make sure the bare metal is clean and sanded. Use a quality epoxy and follow the tech sheets instructions.
I personally recommend waiting at least 24 hours before starting filler work.
Get the metal as straight as you can get it. Don’t pile on too much filler a one time. Thin layers are better than one thick one.

 

Before I fade into the sunset...Richard FWIW I still don't skim coat the entire car. I spend my time getting it straight and I believe with the new primers you can prime and block it straight without a problem. Now I'm not talking 80 coats of primer to get it straight!!! But most of the primer ends up on the floor also. Guide coat is your friend. Lippy

 

Dp-40 was green and Dp-90 was black. The last time I bought some (many moons ago) the new stuff was DP-40LF, which I still have. I haven't painted with anything new in a while and I'm still using my left over Acrylic Urethane. Squirrel said Acrylic Enamel, do they make that again?, here in California they outlawed it in the early 90's? (but I still have some). I like the way the Acrylic Urethane flows out as it dries......but it's kinda toxic.

To add to the post, I've done it both ways without ill effects, just use a good filler. But I'm with Squirrel, easy, semi quick and not a show car (but a driver).

 

I feel that the liquid consistency of epoxy primer allows it to flow into and therefor coat the pores of the metal surface better than the far less liquid consistency of filler.
In this method the metal surface is completely sealed before filler is applied.

 

Truth.

This is the very reason I put down epoxy primer first.

I wait 10-days after filler.


And that filler is under epoxy primer.

 

Spoken like a true Zen level "Slack-Master"...a philosophy I've lived my life by

 

I'm with Anthony. If i strip a panel to bare metal, I'll spray a coat of epoxy, DTM, or self etching primer. But i always grind my area to be filled. I've never had an issue or a comeback.

 

I’m not too sure how many people will understand stand what the Rockwell scale is. Hrc is most common! I saw a 65 number and that’s very hard.


Sent from my iPhone using The H.A.M.B. mobile app

 

Telling on myself here but It happened a lot in the 70's and early 80's at least. I knew better too but when I chopped the 48 in 1981 I got in a big hurry when the event I wanted to take it to was just days away and I didn't take the time to work the metal as well as I should have nor did I weld it up so there were no holes. Hence the rust lines and cracks now.
I remember some local know it all charactors back in the 70's saying that you wanted to leave the holes and have the filler squeeze though the holes to help it hold the filler to the metal better. Probably the source of a number of rust out behind the bondo rigs around.
Still this shot shows why you don't leave holes in the metal when you go to put filler on and also shows why you don't lay in the mud in place of doing a better job on the metal work.

 

It amazes me that some jack leg body man could slather bondo on a rust bucket a half inch thick and it will stay there for decades. We all go to all this trouble to make certain that we do it right. In spite of that, it will occasionally separate and will always shrink...eventually. I guess that's just life.....

 

LOL Rockable. I like you have seen shit that looked wonderful. Magnet fell on the floor on a whole quarter panel. Customer said does that mean trouble? I said yeah you could probably say that.

 

metal sweats?
heat draws in moisture?

 

I have just purchased back a vehicle that I customized from '72-'74. Some off the earlier panel work was painted with red oxide primer then had a skim of polyester based filler. Towards the end a panel beater friend told me they just skimmed over bare clean metal which is what I did. About 50% of the areas done with the red oxide have rust in the steel however the areas where there is filler over bare steel are going to need new steel panels welded in. The original paint is still there but it has been scuffed and repainted. The complete underside and sills were undersealed within a couple of months of the original paint job. I am now going to epoxy paint any bare steel before any filler. I may also use marine expoxy filler this time.

 

Thanks guys! I'm definitely leaning towards using the epoxy primer first, especially because this was my first time doing metal work, so it is far from perfect. It definitely doesn't look professional, but I'm learning. Another question; what should I use to clean off the sanding dust after sanding the filler I have (Evercoat Z-Grip) before laying primer over top of it since it absorbs moisture? I have some prep-all wax and grease remover, would that work?