foam filled plastic bags????

[Burntboot]

So I am in the middle of a "small" repair to the rear 1/4, behind the slider. Seems to be a common area of rust.
Gotta laugh every time I see someone refer to it that way.
I started off thinking I was into a 3-4 day repair, that was 3 weeks ago.

Anyway, when I pulled the rear bumper off, stuffed inside the rear box section, outboard of the bumper brackets, I found a plastic bag filled with foam on both sides.
I have no idea why they are there or what purpose they are supposed to serve or if they are even "original equipment".

This van was supposedly accident free and original paint. What I found was a 1/4 skin poorly welded on with lap welds and a ton of bondo hiding the mess. Gotta say whoever did it, while not a competent welder was a master with mud, I had no idea what was hiding in there. Further, they used expanding foam in the lower sections which, turns out, does an excellent job of holding moisture against the panels, promoting rust.
I am nearing the end of this nightmare but am undecided about the little plastic bags.
I am tempted to assume they were an add-on and delete their existence but figure maybe someone out there can advise if they actually serve a purpose.
Seeing as they are actually real foam - not the expanding type, there is a small possibility they are original???

Thanks
BB

[timsrv]

They are factory. I've also encountered these in the same area on more than one occasion. Purpose? I think they might be for sound deadening (Just a guess)? I can't think of any good reasons to leave but I know long term contact with other materials can accelerate rust, so I usually remove. Go with your gut. Tim

[Burntboot]

Thanks Tim

Out they will be, I would rather deal with a little noise than more rust.

BB

[boogieman]

so today doing a little bumperectomy...need to fab up a hitch for the bicycles....i pull the little baggies out, fire up the compressor and begin to blow out the 30yr accumulation of dirt rocks and whatever...well in my forward thinking i closed the hatch to keep dust inside the cabin down...haha no dice...i pretty much blew all that dirt up inside the van as my cargo has no side panels right now... think those bags are a barrier to the inside of the van..dirt, fumes etc

[Carbonized]

.... and wild life like rodents, lizards, insects etc..

Expending foam (the 2 parts polyurethane) is ok if rust isn't already there and you can guaranty drainage in case of water intrusion. In areas like the bottom of the quater panels where water will get, through the tail lights, it is better not to have any thing.

It is amazing how hard its is to find a real good sheet metal craftsman these days. I' m having to get my own hammers and dollies back to work to redo a job that I paid good $ for. That is after grinding between 1/4 and 1/2 inch thick of bondo off. Not to mention the rust that was left under that mud!

[spacecruisers]

i was planning on installing some insulation/sound deadening material in my van since i have all the panels removed currently, but the van does have a bit of rust. i saw this thread and it got me worrying that this is going to exacerbate the rust problem. am i understanding correctly? Is there anything i can do? I do a bit of camping out of the van and it would be nice to be able to get it ready for the cold weather this fall and make the cabin quieter on the highway.

[boogieman]

Noooo expanding foam!!!!!! i just spent most of an afternoon digging that stuff out of my panels slicing my arms up in the process...PO filled the panels and yes rust was staring to grow...i can see maybe using a dollop or two to secure some sort of hard insulation but thats it...

[spacecruisers]

What about something such as this? There are quite a few Dynamat-style alternatives out there that are pretty cheap? Or perhaps just stuffing it with good old fiberglass insulation that they use on houses? or will that cause the same rust issues?

[Carbonized]

i saw this thread and it got me worrying that this is going to exacerbate the rust problem. am i understanding correctly? Is there anything i can do?

Yes: deal with the rust first! Remove and/or etch before putting anything over it.

Light surface interior rust caused by repeated condensation : wire brush + etch with "ospho" or alike. Heavy, flaky, bubbly rust caused by standing water: Find and remove cause + grind + etch + seal /prime. If you are using sound dampener material, use the proper Butyl base stuff not the Home Despot roofing asphalt based one (it's your health!) and pink fiber glass insulation retains water forever so stay away! I prefer Blue Styrofoam glued(3m super77) to body for no squeaking

Hope that help.

[boogieman]

yeah that stuff looks good for insulating the walls and engine compartment/lids...keep the drains clear at the rockers...and actually for what it did at the rear bumper, the foam filled plastic bag is not a bad solution...

[Carbonized]

Noooo expanding foam!!!!!! i just spent most of an afternoon digging that stuff out of my panels slicing my arms up in the process...PO filled the panels and yes rust was staring to grow...i can see maybe using a dollop or two to secure some sort of hard insulation but thats it...

I totally agree with you on that! If you can avoid it stay away! On the other hand if you absolutely need it, using the right foam the proper prep. and technic for the area I would consider it. Like the rear bumper box for exemple, I would blow the foam into a zip-lock bag inside the cavity.
I never used it myself but they have been blowing insulating foam inside metal building for years, same in steel and aluminium boats. I think the trick is not to create yourself a reason to have to dig it up latter, like existing rust or moisture , or plan in making it removable.
I could see pouring the 2 part urethane in an heavy duty garbage bag between the body work and interior panel, and there you go, perfectly shaped and removable insulation brick. I used to make race car seats inserts that way