My Putty Cracked

Hey everyone. Some of you know that I started up the V-dub GTi project and have loads of thinly applied layers of bondo. Every time I sand it, it has been able to dry and harden for about 10 good hours. However, last night I was wetsandin with 150 and 240 paper and I noticed quite a few hairline cracks. I don't get it. I built some support bars from brass for the inside of the car so nothing is stressed while it's being sanded. So, I've sanded it all down.

Here's my question. Should I strip all the putty off and start over with Tamiya Epoxy Putty? Wait a few more days and apply thinner layers of bondo? Purchase epoxy putty (isn't this like the best damn putty in the world?) and apply that thinly over my bondo and let it dry a day then sand?

Well, hate to say this but that's what you get for using bondo spot putty. It's not ment for big project's like that. I recommend Bondo Body Filler. Sand that smooth and then the "pin holes" you fill with the spot putty.

Well, I just threw the car in the box and the projects on hold once again. I made the mistake of trying to cut out the doors (hatch was already cut open) and that warped the body, and cracked the hell outta the putty. So, its in the box... maybe in a few years I'll buy another GTi and fix this project back up. Thanks for your reply Josh.

I was going to warn you of that when I saw your project completely mudded, but last time I stuck my nose in peoples putty business I got bitched at like crazy.

You need to part putties unless you are filling pin wholes. Otherwise the putties shrink and crack as you've experienced.

Yea I was waiting for you to say something Mike... why didn't you!? lol Anyway, I'm gona try and get back to work sometime soon, with this stupid left hand, got stung and it swelled up like a baloon. only had time for modelling. Maybe in a couple months, like around December, I might pick up another GTi and start over again, what putty would you suggest, Mike?

I would suggest: Not putty at all. Build it up with plastic - styrene sheet, rod, strip, and whatnot. Use putty only to fill gaps.

kinda hard to do when I'm really just widening the fenders and their flares. I could just melt tons on plastic and sand that, but that's just too much work. Thanks for your post though.

Even if all you are doing is widening the fenders you can still use sheet styrene to make a "shelf" around the arch and then fill the gap with putty. Doing so supports the putty which is more brittle and less flexible than styrene. Take a look through some of the work my members like kunta - he as it down to a fine art. Of course you'll need to use two part epoxy putty for such big jobs. Air drying putty will never set.

Just like Phil and Will said, and then use some Tamiya Epoxy Putty. Dont be worried when it looks like a small amount in the box, it lasts awhile.