cockerstar Posted October 21, 2008 Share Posted October 21, 2008 I know that Bondo isn't supposed to be exposed to moisture because it is a very porous material and will soak up water which leads to the rusting of the metal underneath it. I reskinned the sunroof on my 240z and I'm about 85% of the way done with the filler work, but in the down time when I haven't been able to work on my car the bondo has been rained on a handful of times and it gets the morning frost on a daily basis. I was wondering if there is any way to remove the moisture from the bondo so that all of the work I have done so far isn't lost. I was thinking something along the lines of bringing the car into the garage and using a hairdryer to heat the filler up and evaporate any moisture that it's holding onto. The only problem that I see with this is that bondo degrades under heat. Although I am unsure as to what temperature it goes at though. If I have to sand everything down to the metal again I am considering having a body shop do it so my roof comes out 100% straight and true. It all depends on their quote though Any input you guys have is greatly appreciated! Thanks in advance Quote Link to comment Share on other sites More sharing options...
Tony D Posted October 21, 2008 Share Posted October 21, 2008 Grind it off, start over. next time, work it till it's done. A whole roof skimcoated should be able to be worked with a long board to completion in less than 6 hours of concentrated effort. The SEAL it with epoxy primer. In the old days if it was going to sit you used lacquer primer and then whatever lacquer topcoat you had in the gun at the end of the day to stick a seal coat on it to keep moisture off of it. You don't need the filler frinish-smooth, you can always block-sand back into it at a later time. But the KEY is to SEAL it before you set it away and let the moisture get onto it. Any time you work it, and expose filler, make sure to seal it completely before finishing the day. I have had projects in the tropics that went on for three years not have a lifting problem following that simple standard. Seal it well at the end of every working day. And I'll tell you what, before I did the final primer/surfacer and final block sanding, I think I had just about every color of the rainbow of topcoat sealing where I worked. Metallic Purple, Turquoise, Yellow, Red, Midnight Blue Metallic...oh gawd it looked horrible. Black primer covers a lot of that, and added just the right 'blood red' look to my otherwise 'bright red' top coat! Live and learn, eh? Quote Link to comment Share on other sites More sharing options...
SteelToad Posted October 21, 2008 Share Posted October 21, 2008 Grind it off, start over. What he said (every word of it). Even if you get the bondo to completely dry out, the moisture has already wicked its way to the metal surfaces. Quote Link to comment Share on other sites More sharing options...
Evan Purple240zt Posted October 21, 2008 Share Posted October 21, 2008 Start over as Tony said. Bottom line, you don't want to find out you didn't get the moisture out after your nice paint is laid down. Quote Link to comment Share on other sites More sharing options...
AK-Z Posted October 21, 2008 Share Posted October 21, 2008 next time mix some fibergass filler resin in with the bondo. It won't stop moiture, but it will help. Quote Link to comment Share on other sites More sharing options...
cockerstar Posted October 21, 2008 Author Share Posted October 21, 2008 Darn Not what I was hoping to hear, but definitely what I expected! At least it's in the archives now for search purposes. Is there anything in a rattle-can that can be used as an acceptable sealer? Quote Link to comment Share on other sites More sharing options...
AK-Z Posted October 22, 2008 Share Posted October 22, 2008 "Rust Zero" or "POR 15" You can use the crap rust converter stuff that they sell at any schuck, napa, .... so on, It will do the job, but that stuff doesn't adhere to the metal very well. So when you start sanding, on the edges, where the "paint" is exposed, it will start peeling like rubber cement. Quote Link to comment Share on other sites More sharing options...
Tony D Posted October 22, 2008 Share Posted October 22, 2008 For a Rattle-Can, you can spray primer to cover the bondo and give proper adhesion (that is what primer is supposed to do) but then spray over that with lacquer TOPCOAT. Basically any paint meant as a final finish at the viewed surface of the car. That will seal the primer, and it's what primer is meant to be covered with in the first place. You could even do clearcoat. I specify Lacquer because it's pretty much universal, anything can go over it. EPOXY is similar in that it's cured and seals so you don't need to top coat it. But if you are using rattle can primer, likely it's lacquer, and then you have to use lacquer topcoat as it will simply act like another coat of paint later on if you don't sand it all off. Really, the more colors and layers of colors you have, the better you can gauge your depth of cut when sanding later on. Each layer is usually not more than a couple of thousandths thick, and having multiple bands of color exposed in tight rings means VERY likely you will see a divot in the finsihed paint. They need to be wiiiide bands of paint so a ripple or 'work dip' will not be visible in the topcoat. "Feather Edged" is the technical term I suppose. Another thing, final wetsanding should not uncover ANY bondo spots. If you did, your prep and blocking dry was inadequate. Personally I will dry block till I see nothing but even removal of a preliminary guide coat all over the body, taking most of the original primer off...then on respray alternate different colors of primer to give 'depth guides' as to how close I'm getting to the orignal worked area. If you know you put three light coats alternating between red oxide/grey/black and then a thick coating of primer surfacer you can get a real good indication when you have come really close to the working surface and may need to chill out on sanding in one spot. It always amused me when I saw guys wetsanding over bondo. Kinda not the best practices guide to bodywork in play there! Quote Link to comment Share on other sites More sharing options...
Evan Purple240zt Posted October 22, 2008 Share Posted October 22, 2008 Tony, I never thought to shoot more than one color guide coat. Cool idea! Evan Quote Link to comment Share on other sites More sharing options...
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