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Thu May 10, 2018 2:30 am

I have been trying to "touch up" the body - so far without doing the 'full meal deal' of stripping everything down etc etc...

Last year I noticed a messed up area on the side of the van - I think it had been previously bondoed and the bondo cracked, water got in, and some light rust began...
...so I sanded off all rust and applied new bondo - smoothed that - painted with a similar colour rattle can. . .

I KNOW this is just a wimpy temporary solution, but I would like to at least be able to refine my technique so that the repair bondo will at least last for a couple of years without cracking!

My bondo job began cracking after a couple of months! ...now it looks worse than before I did anything :(

Not sure what I am doing wrong...

Thu May 10, 2018 2:51 am

"Bondo" is a great Auto body repair supply but it is often misused creating all sorts of bad reputation for the product.

Anything over 1/8" thick is not ideal....... 1/4" maximum.

Thick layers will shrink over time and crack.

There is no repair for or prevention technique for shrinking/cracking bondo.

The only fix is to work the dented metal to almost the factory shape which requires only the thinnest smear to level out irregularitues.

I suspect your dent is quite deep.

Dave

Thu May 10, 2018 3:07 am

No the dent is minimal and my bondo layer is certainly less than 1/8"... just very thin.

But in fact that bondo has cracked and I don't know why? I think I remember him saying something about 2 types of bondo: 1) base layer, and 2) top layer, and I think I only got one type and skipped the second type.
>>>>> yes I just had a look. What I bought was "FINE POLYESTER" so I guess this is the "top coat". So maybe that FINE stuff is only intended for paper thin applications, and I should have the 'base coat' stuff for the main filling >>>>>

Sound right? Could this be the issue?

Thu May 10, 2018 3:20 am

Ok, what did you apply it over?

Hardener mix? A 4" circle of putty needs a 4" strip of hardener.

Dave

Thu May 10, 2018 3:23 am

djkeev wrote: Ok, what did you apply it over?

Hardener mix? A 4" circle of putty needs a 4" strip of hardener.

Dave

What is Hardener mix?
The guy at the shop said:
1) base coat bondo
2) top coat bondo
3) paint primer
4) paint top coat

Am I missing something here?

Thu May 10, 2018 3:24 am

There are heavy, medium and lightweight fillers. Think of their application like a building a house: foundation, walls and roof.

There are obviously other variables as well. Proper surface prep: enough sanding for the filler to "bite", proper cleanliness of the area where it's being applied and proper sealing of the area after it's application.

Bodywork isn't rocket science but there are techniques that must be adhered to otherwise failure is imminent.

Thu May 10, 2018 3:42 am

I believe you have found out the answer to your own problem. You need to use the proper filler , what you described is for covering light scratches, not for filling dents. Your on the right track, and its a shame because other than that you did a nice job...

Thu May 10, 2018 4:33 am

Bondo is a two part mix. The putty and a squeeze tube of hardener.

Am I to guess you used what I would call a scratch filler on the entire job? Most often it is red but I've seen blue here in the States as well.

Your solution is to remove it all, prepare the surface properly and start again using the proper filler.

Dave

Thu May 10, 2018 4:59 am

Ive got a small section of bondo on a van I own. Was applied after an accident in 86. W/o a magnet most would never see it.
When you have the correct stuff and use as engineered to be used it seems to work quite well.
Im learning something new here though. Had no idea there were multiple types.
Agreed. It has a bad rep and its from rookies w/ putty knives filling holes 1" deep and 8" wide. Mine looks fabulous.
Keep us in the loop. I may need more for a new project Ive found. I'll keep watching and get learned up on the proper tech. :popco
By the way, just used some to fill small holes in my top. You have about a 10 second window to apply this stuff. At least here in the desert it sets real quickly.

Thu May 10, 2018 5:12 am

Thu May 10, 2018 6:41 am

epowell wrote:
Last year I noticed a messed up area on the side of the van - I think it had been previously bondoed and the bondo cracked, water got in, and some light rust began...
...so I sanded off all rust and applied new bondo - smoothed that - painted with a similar colour rattle can. . .

Yes, the single variety you applied is ONE of the issues you are having.

The other is not quite clear, as your description says you sanded off all of the rust. It does not say you sanded off all the bondo. Did you sand off all the old bondo?

Here is a suggestion: Sand off all the bondo, new and old. Get a sink plunger, they are a couple bucks at a hardware store, they are about half as wide as a toilet plunger. Wet the dent and push the plunger into the dent, so you can pull it outward a bit. You will need a hammer of some sort, most folks can invest in a cheepo body hammer set for $15 on the internet. Use one with a rounded face, not flat. It doesn't need to be a very high relief bulge, just some. Now, while pulling the center of the dent, lightly tap the outside most location you see of the dent. Tap tap tap, all around, coming in closer to the plunger as you keep pressure pulling on it. At some point, your pulling will produce a -boink- and the dent will have popped out. Just take your time. Give a little push where the dent used to be and if it pops back in, put the plunger on it again and do the same thing again, tap tap tap, -boink- tap a little more all around. Then pull off plunger. Then if you need bondo, the end product will not continue to have the metal under it flexing. You may not need any bondo at all, perhaps just a light skim of the stuff used for a final topcoat. Its called Glazing putty.

-bobby

Thu May 10, 2018 6:58 am

Generally, manufacturers provide very detailed instructions on how to use their products. They are the last folks that want to see their products fail.

The next time you are at the paint supply store, be sure to get a spec sheet with the manufacturers instructions and be sure to follow them. Most manufacturers have them online as well. Follow the manufacturers instructions and you can't go wrong.

For example:

http://www.evercoat.com/images/ePIM/original/TDSRageGold103612English.pdf

I'm currently doing some bodywork on my Bus. My thread may be helpful to you:
https://www.thesamba.com/vw/forum/viewtopic.php?t=689614&highlight=

Thu May 10, 2018 7:38 am

Most importantly, use good filler like Rage Gold, the metal glaze for the final coat.

Thu May 10, 2018 8:23 am

It looks to me that you may not have gotten rid of the rust behind. The rust is pushing out the bondo you applied.

J

Thu May 10, 2018 8:42 am

Strip the area to clean shiny metal. Straighten the panel the best you can with hammer and dolly. Fill remaining low spots with quality body filler. Shop for Evercoat products. Sand filler with 80 grit. Apply skim coat of same filler and sand with 180 grit. Apply two part exoxy primer over area. I like PPG DPLF. Don’t sand the epoxy. Apply two part primer surfacer (aka sandable primer) over epoxy. For this I like PPG K36. Sand with 400 grit. You can apply the color coat at this point or put an epoxy sealer on and then color. If you are doing a base/clear system then apply clear over the color without sanding the color. Optionally you can wet sand the clear with 1200 and 2000 grit and polish.

Thu May 10, 2018 8:51 am

djkeev wrote: "Bondo" is a great Auto body repair supply but it is often misused creating all sorts of bad reputation for the product.

Anything over 1/8" thick is not ideal....... 1/4" maximum.

Thick layers will shrink over time and crack.

There is no repair for or prevention technique for shrinking/cracking bondo.

The only fix is to work the dented metal to almost the factory shape which requires only the thinnest smear to level out irregularitues.

I suspect your dent is quite deep.

Dave

I mostly agree, but I've gotten away with some thick filler, provided it was fiberglass reinforced.

Thu May 10, 2018 8:54 am

jberger wrote: It looks to me that you may not have gotten rid of the rust behind. The rust is pushing out the bondo you applied.

J

That's my bet.

Body filler is generally very forgiving -- that's why it's so widely abused! But if there's rust underneath, the filler will fail.

Thu May 10, 2018 8:55 am

pbrown wrote: Strip the area to clean shiny metal. Straighten the panel the best you can with hammer and dolly. Fill remaining low spots with quality body filler. Shop for Evercoat products. Sand filler with 80 grit. Apply skim coat of same filler and sand with 180 grit. Apply two part exoxy primer over area. I like PPG DPLF. Don’t sand the epoxy. Apply two part primer surfacer (aka sandable primer) over epoxy. For this I like PPG K36. Sand with 400 grit. You can apply the color coat at this point or put an epoxy sealer on and then color. If you are doing a base/clear system then apply clear over the color without sanding the color. Optionally you can wet sand the clear with 1200 and 2000 grit and polish.

This sounds awesome but I don't think you know a lot about the OPs situation!

Thu May 10, 2018 9:50 am

There is a product called DuraGlass. It is a type of "bondo" body filler, but it has fiberglass strands in it that allow you to use thicker amounts. It is not as easy to sand, so you want to apply just enough that you can grate it to the dimension you want and then do the final fill with the easy sanding body filler. Heavy primer last step.

Thu May 10, 2018 10:04 am

Your lack of A/C is causing the dilithium crystals to precipitate endothermically, ending up in the fissures of shame. Don't. Be. That. Guy.