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Thread: Vacuuming rocker panels and spraying-in expanding foam insulation - thoughts ?

  1. #1
    PhatAssXJ
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    Default Vacuuming rocker panels and spraying-in expanding foam insulation - thoughts ?

    So my '93 XJ I sold about five months ago had a strange problem... it was rusting everywhere. Hah, yeah, real strange. An XJ rusting?! Unheard of!

    Anyway, that rust bucket is long gone; no more 2' rust hole in the PS front floor, no more rusted-through rear rockers, etc.

    But now my new project vehicle, a '93 2-door XJ... well, I wanted to explore an idea, but I'm not gunna do it until I run it by a few of you guys. I thought I might vacuum-out all the rockers and the inside bottom of the rear quarters (thus removing all the loose rust, dirt, debris, silt, etc.) and fill them with spray-in expanding foam insulation (tan foam crap in a can). The idea here is that since that crap is as tacky as can be, seals really well, and is oil-based, it should seal-out moisture and therefore rust, right? I thought spread around some POR-15, let it dry, then spray in the expanding foam, filling the not yet rusted rockers as well.

    Before everyone shoots this down, consider this. . . I took a look in both my '95 Audi 90 Sport, and my '03 Audi Allroad, and BOTH have this SAME expanding foam down in their rear quarters (down in the rocker section). Both Audis are 100% rust free, and the stuff HAS TO insulate against road noise to an extent as well.

    Having read the Audi tidbit, any thoughts? Has anyone done this before? Good experiences? Bad experiences?

    TIA guys!

    Matt

  2. #2
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    Default

    It definately sounds like a good idea for people in areas with lots of road salt.



    Patrick

  3. #3
    PhatAssXJ
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    Which is me.

    This project XJ is from the south, so it's pretty rust-free, right now, but the IL winters will make quick, bittersweet work of it's current state.

  4. #4
    Registered Jerod2099's Avatar
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    The expanding foam alone will not keep water and stuff out. Water will and does find its way through that stuff. I worked at a boat plant that used the same thing (on a larger level) to help the boats float. It will probably help alot but it won't stop it. If you can line everything with that POR stuff then do it you might be ok but the foam holds water very well. When they filled the boats with foam (under the decks and stuff) they used trashbags to help control the foam and to help keep some of the water from getting to the foam. I think the idea is great as long as you line the inside panels with a rust preventative like POR then put the foam in but try to seal off any holes and such that might alow water in otherwise you might hold the water there and cause more damage.
    85 CJ7 258, 105000 miles and counting, motorcraft 2100 and TFI upgrade nuttered, I think it may have a small spring lift but not real sure, 31" tires and 1-piece rear axles.

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    that foam is called polyurathane and you can get VERY different kinds of formulas. I market the stuff here in PR as a roof tile adhesive. It is a CLOSED cell foam thus absorbs very little to no water 6% at 100% humidity for two weeks. that means the XJ has to be under water for two weeks for the foam to absorb 6% moisture...

    the real problem is the curing process.. poly-foams cure from heat created by the mix of the foam and the glue (A+B) and if you pour too much in a cavity the center wont cure well. Especially the stuff you buy at Home Centers in a can. you can use the stuff I sell but it isnt cheap...
    91 XJ black few mods, ARB bumper AND ROOF RACK!!! OME 3" lift & shocks, Mickey Thomson 10x15s, 32" BF Ta Kos, RECARO SEATS, K&N, HELLAS, MoMo Steering wheel, Bushwackers, 1000 watts of hifi and a led foot.... many wishes... mainly that it does not die on me.

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    100% humidity is not synonomous with being underwater. 100% humidity just means that the air is holding the maximum amount of water vapor that it can, ie. saturated. So, in these conditions the foam would absorb about 6% of it's mass of water in two weeks. I'm not sure if that is necessarily bad, but it seems like that particular kind of foam would draw water into itself. Shrug, but nonetheless, this foam will absorb water - and when put in direct contact as opposed to just air humidity - probably a lot more than 6%, as that statement implies no limit on the maximum amount of water the foam can hold. Just some thoughts do what you want.
    2001 XJ - getting there, as fast as paychecks allow

    93 XJ - SOLD

  7. #7
    Registered Stick 89's Avatar
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    Default foam

    If the foam does draw moisture,would this not cause mold to form?If the mold does form wouldn't it eventually rot,if it rots would it not smell like somebodys socks that hadn't been changed ...............ever?
    I really like you people...You remind me of when I was young and stupid

  8. #8

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    get some por-15 in there, that should be all they would need to be rust free.
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    Default Re: foam

    -=- originally posted by stickboy -=-
    If the foam does draw moisture,would this not cause mold to form?If the mold does form wouldn't it eventually rot,if it rots would it not smell like somebodys socks that hadn't been changed ...............ever?
    Exactly.
    I bought a 67 mustang for restoration. The dork that had it before did an excellent job on preserving it....except the rear bottom quarters. He shot foam in. They were the only rust on the vehicle.
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    umm... they can't rust if they're not there












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  11. #11
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    They used something like this on Monster Garage when they made the VW Swamp Boat. It did absorb water and nearly sink, so I guess that means it's not a "closed cell" foam. Maybe fill it with foam and then cover it in rhino lining, or something?
    Brad Bray
    Savannah, GA
    1996 OME XJ, "Badger"

  12. #12

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    There are different urethane foams available for different purposes, and they cure in differnt manners.

    Do NOT use the home center-type of stuff. It requires atmospheric moisture to cure. Will NOT cure in a closed metal space.

    The two-part foams cure like an epoxy, where the catalyst combines with the resin and a chemical action commences. It gives off a little heat which helps with the chemical reaction, but the heat itself isn't the cring mechanism.

    For several years, the european and japanese manufacturers have been injecting Structural Urethane into stressed members like rockers and A,B,&C pillars to stiffen them and deaden noise. These are much denser than urethane foams intended for thermal insulation.

    I don't have any links, but I recall a similar discussion 3-4 months ago either here or Naxja regarding the proper material and sources for it.

    -Rick

    PS: Be sure there's no active rust inside the panels. If there is, just sealing it with POR or something else will allow the rust to continue eating it's way outward.

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