Anybody fill the area between the trunk / fenders?

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airwoofer

airwoofer

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We are replacing the patch panels on my Demon and the trunk extensions are pretty much still there but are missing some in the front. This has been a race car a long time and I think the burnouts took their toll. The body guy is thinking of filling the area between the new patch panels and the trunk extensions. Supposedly this "structural foam" is the solution to moisture getting in there, as well as crud and debris.

Anybody ever do this? What do you body guys think?
 
I would really suggest against it. I am certainly no authority on current body work practices, though all my experience has lead me to find that foam and its many "pores" or basically all the tiny bubbles that make up a foam of any type, will have the potential to hold moisture.
There are of course "closed cell" foams, that are literally what the name implies. All the bubbles are closed and there are no passages from bubble to bubble. I would assume at the very least that it is a closed cell "structural foam" that is on the market.

However... As someone who has fixed many-a-rust-repairs, as well as the quarters on my little Valiant, I would say just repair it with sheet metal, drown it with Ospho, and leave the area accessible for future treatment.

Two things on that note. It took many years for the rot to become an issue, and most likely that was when the car was driven daily in who knows what kinda of weather. If the repair is done well, and then treated correctly with a sealer and rust inhibitor, it will last longer than it ever did the first time.

I cant take credit for this idea, however I have certainly used it and will again.
I used Ospho (a rust inhibitor / converter) and used it in two ways.
1. I poured it into the 1/4 panel at the rear most part and let it saturate the seam weld. It then poured out into a paint pan, and I continuously repeated the process for a few days, letting the 1/4 drip and dry.
Ospho easily has the same viscosity of water possibly less. It literally penetrates and saturates deep into all the seam and converts and stops the rust.
2. I put Ospho in a spray bottle and sprayed the entire inside of the 1/4. I sprayed the areas with under coat as well. Seems pointless, but in a few spots I noticed where the opsho must have found some rust as it discolored a few tiny spots as it did when it reacts with rust and bare metal.

Again, my take is to stay away from foam in the areas that have a great potential for moisture. Not to mention.... I have done the "foam repair" when I was in HS.... It turned out to be the major contributor to the repair being needed years later. It had actually trapped moisture. Granted..... It was the foam in a can "Great Stuff" and was NOT intended for the use I did! Hahaha

Sorry for the long winded answer.
 
No,dont foam it!!! leave it open after patching just like OEM, POR15 or rust paint treatment simular is your best bet! There was actualy a body plug in the extenssion that acted as a drain, not very effective but the factory did place one there.
 
when you see one of those large motor homes go by remember foam is about the only thing holding them together ,I would say use it. just my 2 cents.
 
teringer said:
when you see one of those large motor homes go by remember foam is about the only thing holding them together ,I would say use it. just my 2 cents.
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there mostly foam and ALUMINUM though, foam on metal is a really bad idea, foam holds water and will rot metal inside of a few years
 
Foam is great! :cheers:
 

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Foam....fender in a can! LOL....Just say'in :)
Now you know where the kids pillow went after that long road trip!
 
Yeah go for it. Then after time you'll know why you shouldn't have.
 
The guy just threw it out there and I said I would keep an open mind. It would have also hid the seam from the patches.
 
Darnut, Looks like to me a little more foam, sand paper and paint and you'll be good for another couple of hundred miles. I looked at a car about a year ago where the guy had used Hilti construction foam skim-coat primer and paint on the lower rear quarter panel. When I was looking over the car something just looked wrong when I was looking down the side for waves in the sheet metal. I wasn't sure what looked out of place but it just wasn't right. When I pulled out the magnet he told me what it was and said the rocker panel was just too expensive and when this one got beat up all you had to do was carve it out and apply some more foam and sand to shape, and unlike bondo it wouldn't crack and fall out. I will give him this, the Hilti foam has a very low moisture retention and is some of the strongest foams in a can you can get. That experience really made me look more carefully while I was searching. Remember once it's done your name is the one on it.
 
Use a seam sealer if you're gonna use anything for sealing seams. Down in that area, I would recommend 3M's Rust Fighter. Spays in with a wand in tight spots, never dries and has the consistency of petroleum jelly. Slide in the wand from the top and from the body plug on the inside of the extension panel.

Good luck. and I agree.........find a new body guy. Foam is horrible.
 
High end vehicles haxe foam in those sort of areas to serve as sound deadening and insulation. They have the foam fill and a plastic bag and shaped so it can be removed and put back again. This is likely what your body man has in mind.
It's my belief that all the nasty found in that area came from a failed trunk lid seal above rather than up from the road. What gets in around a quarter glass should stay in front of the wheel well.
 
I'd sooner fill it up with seam sealer, welding it up sounds right to me though.
 
The quarters are cut to the body line under the marker lights, patch panels (Goodmark, AMD won't make 'em) trimmed to fit. Trunk extension cleaned up as best as can be for a car that has had the wheel opening enlarged at the rear. The Goodmark patch panels seem thicker than the OEM metal BTW. Gonna lap seam them in on the backside and will grind and seam seal.

He just threw out the idea and I was gonna see if anyone had tried it. Not the cheap insulating foam, the part A / Part B foam, but the high dollah auto body stuff. I at first didn't like the idea cause I have seen too many cars that filled the area with whatever and bobdo'd the outside smooth and shot the paint.

The stuff we found in there... Drill bit, wing nuts, lotsa dirt and grime. No wonder they rust out.
 
Why not get a block of closed foam and make 4" tall form fitted insert plugs to block crap from falling in but still allow access incase you want to get in there?
 
Rice Nuker said:
Why not get a block of closed foam and make 4" tall form fitted insert plugs to block crap from falling in but still allow access incase you want to get in there?
Click to expand...

A 96 Camry ( among a few examples ) has plastic trays that sit there.
Not much for storage but a catch all anyway.
 
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