Bondo everywhere I dig!?!?!?!? What to do?

[techrat]

Was it/Is it considered a standard practice amoungst some folks to use a thin coat of bondo over the entire surface of a body panel? (Every Body Panel?) during preparation for paint? In the process of doing some exploratory surgery on my car I am coming up with a thin coat of bondo almost every where I "dig" .
I guess regardless of whether or not this was considered to be conventional wisdom at some point in time, it has been applied to my car.
How should I deal with this?
Will media blasting remove thin coats of bondo?
Does it need to be removed? (I should mention that I have spots of surface rust pushing the bondo up in some places.)
How do I deal with this properly?
Any help will be appreciated! - Techrat

[Bill77]

No easy answer here because it depends on the overall condition of the car, how well the bondo is adhering and how much time and/or money you wish to commit. If you want a really good paint job that you can have a reasonable degree of confidence will last for a while, the bondo should be removed. Media blasting will be able to remove the filler, but be prepared for what you might find underneath. The car was skimmed with filler for a reason! It might simply be to straighten out wavy or dented surfaces, or it might be to cover up rust or shoddy repairs. I stripped bondo from my car and found several sizable dents that were very poorly straightened.

As a rule, filler thickness should not exceed 1/8". Good quality filler applied to properly prepared surfaces should last for a long time. Bondo gets a bad rap, but "filler", when used properly, is fine. There are many, many bad filler jobs.

It could be possible that what you are seeing isn't Bondo or filler. It might be a sprayed-on primer-surfacer or high-build filler primer. These products are often used to allow block sanding to get to a perfectly flat and straight surface. No matter what it is, if there is cracking or if it is starting to come loose, you are better off removing it before spending time/money on new paint that won't last because material underneath is coming loose.

[tubut]

Techrat,

I'm not sure what car you have but I can tell you that bondo (or filler) coating up to 1/4 inch near seams used to be common on 2600 Touring Spider and on 2600 SZ cars manufactured in the 1960s.

The reason seems to be that these cars were essentially handmade by Touring and Zagato with panels that were warped and had poor fit. One 2600 SZ owner I talked to told me that after he stripped the car, he was surprised that almost all panels had hammer marks as if the car had been exposed to a hail storm. The bondo was used to cover these marks and even out the panels.

However, I would not expect that an awful lot of bondo was applyied in the manufacturing process from the 1970s onward.

With respect to your questions:

If rust pushes up through the bondo, as you describe, you need to strip the body to bare metal. Media blasting will remove the bondo, but keep in mind that what you paying for is time and material. It may be more effective to strip the car manually using a chisels, sanders and wire brushes.

Chances are that you'll encounter rust that has grown from the inside out. You'll need to tap down the car with a small hammer and listen to changes in sound.

Hope this helps,

Ruedi

[jrreeve]

If you have to strip the car...use an aircraft stripper, all the other crap doesn't work. Just paint it on, watch the paint bubble up and take a putty knife and remove it. I completely stripped my car before repainting and removed all of the body work that was on the car with a DA. A good sander/grinder will take it out fine.

Here is what the hood looked like after i stripped it with Aircraft Paint Remover.

Rob
'84 GTV-6

[ossodiseppia]

I like to watch car shows on cable like American Hot Rod, Rides and Overhauling. On every one of those shows, I've seen the body guys slathering on body filler like there is no tomorrow. They seem to coat the entire car with the stuff and then spend hours and hours sanding it and sculpting it. I can't imagine why.

Body filler does not seal or protect the metal. Body filler likes water. If there isn't any primer under it, it's can cause rust. The sandable primer filler that Bill77 describes is what any good shop would use. I hope that's what is on the car.

[Touringspider]

A lot of production or high volume bodyshops will use a "skim coat" of filler over panels. It is apparently faster and cheaper to slap on the filler and then block sand it flat instead of doing a bunch of hammer and dolly work and metal filing to smooth out dented or wavy panels. As was previously noted, modern (and good quality, since there is some cheap crap on the market) fillers definitely have there uses and can be quite durable if properly mixed and applied to a properly prepped surface.

Filler has gotten a bad reputation when bodgers apply it over holes and damage, an application which is totally inappropriate since it has little if any structural strength. There are some aluminum based fillers in a styrene carrier that claim to be "bridging fillers" to cover pinholes and such, but my experience with them has been spotty.

As for the original question from the poster, if it appears that there is rust underneath pushing the filler up, take it all off and start from scratch. The aircraft stripper (what is up with that name?) is great stuff, but remember that it will soften any filler underneath, so if you use it you better take the filler off too.

As an interesting datapoint, I recently finished stripping my 102 series Touring Spider back to shiny metal in preparation for painting. Although Ruedi mentioned that the Touring bodied cars had a lot of filler, I was fortunate to find a lot of lead instead of filler. Now, the car apparently took a hit on the nose at some point and some cowboy reshaped the nose with a couple inches of cheap bondo, but I count that as a bodge job. The body shop has been able to hammer everything back out and add metal where required.

Good Luck,

Arno Leskinen
AROC National Concours Chair
Gilbert, AZ
102
115
116

[tubut]

Arno,

I probably should have been more precise: Touring for sure used tin/lead in a lot of areas. The cars I've seen with filler are 106 Series 2 cars that used a combination of tin/lead (e.g. to even out the three segments of the rocker panels) and filler (on the side of the front fenders adjacient to the rocker panels).

Can't wait to see pictures of your car!

Cheers,

Ruedi

[techrat]

Thanks for all of your input! I suspect that what I am looking at is a job that was done with a skim coat of filler over the entire surface. The thickness is less than 1/16" in most places and I will likely remove it as I go. In many cases I suspect that I will be replacing entire panels with new metal so it may not matter so much. I am in the exploratory phase right now just trying to find out what I can do and in what time frame. MY first priority is to stop the rust from getting worse. By the way the car is a 65 105 Giulia Sprint GT
Thanks Again!

[CarPoor]

If you do end up needing to strip the car bare, I used Jasco stripper (household product, nothing expensive or special) to strip my Berlina's OEM paint to bare metal. It also softens the bondo and makes that ready to peel off also. One caveat: Make sure you thoroughly rinse the car with water when you're through with the stripper, cause they will play heck with the new paint if there's any left in the nooks and crannies when you respray.

[Bill77]

Does media blasting affect the lead fillers used in some of the panel joints? How about chemical stripping?

[tubut]

Bill,

Yes, media blasting does indeed affect tin/lead fillers: it creates holes in it and some blasting media particles may stay embedded in the filler. No matter whether you strip the car chemically or through abrasion, you need to put at torch to the tin/lead filler and remove whatever is there without overheating the metal around it.

Hosing the car down after media blasting or chemical stripping just leads to the next problem, known as "mill scale," "micro rust" or "surface rust": Oxygen and moisture in the air immediately start to react with the bare metal, resulting in new and often invisible rust (until the paint starts to bubble again 2 years later). Hosing the car down (or touching it with bare hands) makes the problem worse and accelerates that kind of rusting.

Hence, it makes sense to protect the car after stripping as soon as possible, by using a degreaser and etching primer. If applying a coat of primer is not an option (e.g. because you can not do the whole car at once), try an anti-oxidant such as www.picklex.com.

Ruedi

[Larry G]

I've had pretty good luck on stripped-bare panels using Oxi-Solve from Eastwood. It takes the (seemingly instant) rust coat formed on bare metal off and gets it ready for prep solvent and etching primer. Hang in there, it's all worth it in the end.
Larry G

[CarPoor]

Reudi/All:
I was told by the folks that did the paint on my Berlina that the "microrust" that forms so quickly after washin bare metal isn't a problem...then again, it might just be that it isn't a problem for them, cause they get repeat business after your paint job starts to fail in 2 years. It IS critical to remove the chemical strippers, though! I guess I will use the chemical stripper next time and sand the bare metal IMMEDIATELY before applying barrier coatings/primers etc. Pics of the Berlina's stripping process attached.

[SuperFab]

For my 2 cents...

I highly recommend chemical stripping...send out the parts whether they be a door, hood or entire body shell. Once the parts are done, there are no surprises later on. Everything disappears except the steel...where there was rust, you will have holes...period...no more paint, bondo, tar or anything dirty. Be forewarned, it isn't for the faint of heart!

[tubut]

In my opinion, a lot of the discussion about chemical stripping (and by that I mean dipping the car in a chemical solution, not using a bit of gel on a surface) depends on the age of the car and the knowledge and production processes that were in place at the time of manufacturing.

Cars of the '50s and '60s were pretty much hand made and spray painted. In the late '60s and early '70s, the manufacturing changed to high-volume production using machine-pressed panels for unibody cars that were dipped in paint. This is significant with respect to design of draining channels: If surplus paint could leave the body after dipping, hopefully chemical stripper (and surplus blasting media) will do the same. However, in cars of the '50s and '60s that were not designed or built that way, there are cavities that will trap chemical stripper and surplus blasting media.

With respect to micro-rust, the issue is whether or not (and for that matter, how quickly) the oxygen can be trapped to prevent oxidization of the bare metal. Many rust-converter primers do just that: prevent oxygen from reaction with the metal. The trouble starts if the bare metal is left untreated. I was told by a local media blasting company that they do not blast cars under certain weather conditions because customers cannot pick up the cars quick enough and surface rust starts to form.

At the end of the day, it seems to me that there are only to points to remember: (a) be gentle -- no matter whether you choose a chemical or mechanical procedure -- and (b) protect the bare metal as soon as you can.

Ruedi

Ruedi