Customs How much filler is too much filler?

I'm working on a full custom build and it looks like the front fender had a bit of a bump awhile back and the repair was handled with a slide hammer and a lot of filler. I've ground off the filler in a few spots and it seems to cover the entire front end, both fenders into the rockers. I haven't seen any sign of rust after scraping away the undercoating on the non-filler side, or in random spots in the lower fender and rocker. The thickest filler seems to be less than 1/8", although it's difficult to measure.

I can't afford to have the car dipped or professionally sandblasted. It's a unibody and replacement panels are very expensive. All the gaps are good, everything fits nicely, doors close better than my modern car, there seems to be no rust and everything is straight. The filler seems to be good quality (not Bondo). The primer looks old and cracked in a few places (it has been in storage in Texas for decades; no idea when it was painted) So, what would you do? Fill in the filler divots I made and move on? Remove all that filler, assess, and likely have to reapply most of it?

 

Looks thicker than 1/8” to me. For one thing I’d never leave the slide hammer holes. And, if you can get to the backside, you will be amazed what a little time with a hammer and dolly can do. I doubt you could hurt it worse.

 

1/8" is fine, and for a car like that up to 1/4" would probably be acceptable....

Then again, there are a lot of variables in play, and it usually boils down to how much time/money you want to put into the car, and what will be done with the car when it's finished?

 

How is the final paint going to be ?

the fact you have disturbed the filler I would grind it all out and start fresh with new product .

you can metal work the areas and get it better or closer so less filler is used

I got a buddy who will not use more then 3/16ths of filler

I think up to an 1/8th is ok


Heck I’ve rebuild rocker panels and doors with INCHES of filler !!!!

All depends on what you want the end result to be .

 

1/4" is as deep as any filler company recommends.

If there were no holes I would say leave it and run with it but the holes are a kiss of death to filler as it will absorb moisture at some point through those holes and fail. If there are holes there there are probably holes other places as well.

If it was me and I planned on paining it I would take it all off fill the holes repair the metal work as much as your skills allow and reapply. If it just getting a coat of primer and I am trying to fix it on the cheap I would try and see if I can find any other holes from the back side of panels remove the filler in those areas fill the holes, fix the spots and live with the fact I might have missed something and I might have issues down the road.

 

You dont want holes under the filler. Its extreemly porous water and will corrode the surrounding metal. Looks a bit like an early 60s jag.

 

I strive for 1/16" inch max thickness, but settle for 1/8" max.

 

I should have specified that I will definitely fill those holes. The backside was covered with old undercoat. I don't think the car has been on the road since the 1970s, but I have no idea when the "repairs" were made.

The plan is for a nice paint job.

If the best approach is to strip it all off, what is the best way to remove that much, well-adhered filler? I have to strip at least some of it of to do some custom modifications, but ALL of it would be a lot of work.

 

I agree that some of that looks thicker than 1/8", so I'd work to get it closer to 1/8" myself. And I'd weld all the pulling holes shut, and dolly the areas wherever possible.
I use All-Metal filler direct on the metal for anything that's close to 1/8" thick first. Then once I knock down that filler, I shoot the whole car in epoxy sealer, and begin the process of skim coating, and doing the rest of the bodywork. I'm not a professional body man, but this has always worked for my builds.

 

I just double checked (with glasses on!). The thickest part is just a hair over 1/8, but it does look thicker than that. I'm not sure why it's so thick there since it's the furthest from the dented fender.

 

My can of Evercoat Rage Gold says up to 1/4". I feel like the people that make it know better than I do.

 

MAPP gas torch and a putty knife will take it off

 

My experience is that since you have disturbed the current filler, it all needs to come off.
The new filler will not stay bonded to the old filler very long. in about 2-3 years, you will have cracks form in the paint where ever you have tried to mix the old filler with the new filler. Doesn't matter how thick either filler was, or is, they won't stay bonded together.

A max thickness of a 1/4" would be the desired goal, but the fact is, after you have covered the metal, you won't ever know how thick it really is. So you do the metal work to as close as you can, then fill it and sand it smooth, and paint it.

Mapp gas and a putty knife will probably remove it the fastest, but don't catch it on fire, you just heat it to soften it up, and scrape lightly so you don't gouge the metal. The other option ( and maybe the final run at it) is to grind it off with course paper on an orbital sander, you need to remove all the old stuff.

 

A DA or a SCT (surface conditioning tool) should take it off pretty well. I've never used the MAP gas method.

 

I caught my 64 impala on fire after a backfire and it came off the hood pretty well.

 

I didn’t know about the MAPP gas/scraper deal years ago, but my Dodge had every dent filled with Bondo, no metal work attempted at all.
I used a fine wire cup brush on my angle grinder, made quick work of it, and a mess in the garage

 

Wear a good mask when grinding off all that filler.

 

Baking it off and scraping is a lot less dust.

 

If you take a small wire brush wheel and use an air tool the round shape will get down into the small dented areas and remove the filler. Since you plan to weld(?) the holes closed, the heat would ruin the existing filler and the filler might interfere with the welding.

 

Never enough filler! Just use the lightweight filler

 

An eighth inch wouldn't bother me, but cracked primer and slide hammer holes would. If this is intended to be a nice finished car, I'd do as others have suggested. Strip the fenders, weld up the holes, metalwork the sheetmetal to the best of your abilities (even if you can only get mild improvement, still seems worth it) and then skim coat the fenders again and re-block them. If you have to use an eighth in places to get it right, so be it, that's not the end of the world.

If I were intending to put real, finished paint on it in the end, I wouldn't try to tie it back into old filler work once it's been opened up. And I wouldn't want to paint over that old bodywork without seeing what's underneath, even if I couldn't get it any better than they did in the end.

 

I guess I'm going to be investing in some respirators and a truckload of filler.

 

Just my opinion with no practical experience.
The holes behind the filler will create a avenue for moisture. That will cause the bondo to fail.
How long depends on your climate & storage. ..... If the car lives in a garage & never sees rain it might last forever.

I agree with the typical answer on the can says 1/4". That's what the manufacturer will guarantee.

Lets ask famous car builder Barris "How thick can you go?"
I would suspect he does decent sheet metal work & keeps it to a minimum thickness, but has gone past 1/4" many times.

We could ask Bad Chad ..... makes me laugh so hard thinking about him ..... I'm sure he measures in gallons & not inches.

Point is, custom cars since the beginning have been piling on the bondo ..... difference is the initial surface preparation.
The past bondo needs removed to seal the drilled holes, once removed is possible you can do better then the last person ..... As others have said, new bondo wont last applied to old bondo so you remove the old.

You do not own a welder? .... fine, use J-B weld & seal the holes then fill it with bondo.
This is a terrible solution, but it would work. I'm hoping you can do better.

My only point with the suggestion is, do not let it stop you or discourage you from working on your project.
So many projects get side lined then sold off for pennies on the $$ because they think they need something they cant do or afford. Just do the best you can.
You can always re-visit this area later as you learn & progress your skills .... Just accept you are not a master craftsman & move forward. You learn as you move forward.
Do the best job you can

 

Lol , this was done on winter beaters as we call them up here .

mono foam , carve to desired shape , bondo , rubber rock gard , paint .

works for the 3-4 months I need the car then sell it or scrap it once I’m done .


Crappy body work in some instances is still better then rust and holes , but not on something I care about .

 

My experience from when I didn't know better says that those holes (that let the bondo grip better) let moisture in behind the filler and let the metal rust behind the filler.

This was back in1980/81 when a lot of didn't know better and our skills may not have been the best and the patience to take the time and effort to do it right was sometimes non existant. There weren't any internet photos of guys doing perfect metal work in those days, you just talked to your buddies who were well versed on how long you let bondo set up before you took the cheese grater to it to shape it and you were big time if you had a real long board to sand it with.

 

@K13 are there any fillers that don’t absorb moisture? I figure you’d know, was just curious.

 

Regular body fillers and putties? No. They all contain talc which is what absorbs the moisture. What we call specialty fillers that use substances other than talc for body/strength yes there are some that will not absorb water. Short and long strand fiberglass fillers, aluminum based fillers, kevlar based fillers none of these types of products will absorb moisture.

Generally most talc based body fillers will last about 200-250 hours in a salt spray test before they begin to fail.

 

Thanks for the reply. I don’t have a need, but figured you’d know things like that.

 

@VANDENPLAS ...... It's a Dodge!

I understand totally, I'm not good at bodywork. I'm working om my first truck project.
I bought it in 2018, I have no idea about creating patch panels. I did have a welder but had to learn how to use it .... I took almost 1 year off working on my truck while I taught myself to weld.
Now I'm comfortable welding in body patches ..... Sometimes just having the project is the fun.

I'm only suggesting, we need to learn to crawl before we can walk .... before you know it we are running.
Suggesting the fastest way to run, while the recipient is trying to learn to crawl .... not always the best advice.