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Removing Sound Insulation From Chassis

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  • Removing Sound Insulation From Chassis

    New post: April 9th, 2020: On a street car you will want to have some insulating materials to keep hot bits from the engine or exhaust radiating heat inside the cabin, as well as road and exhaust noise from driving you nuts. BUT whenever we prep a car for dedicated race use there is "easy" weight that can be removed in the sound insulation, which in most cars over the past 30+ years covers the floorpan, firewall, trunk, and often the door skins. This stuff is adhesive backed and made out of some sort of asphalt like substance. There are two proven ways to remove this garbage, which I detailed originally in this forum build post and have re-posted here.

    You CAN damage the floorpan finish if you aren't careful, so maybe read these tips below from previous forum build thread post on our Team Vorshlag endurance race car build using a BMW 330 coupe chassis. This car is still a work in progress as I write this, but we have used this job many times in the past on lots of cars.


    We already removed all of the carpets, dash, door panels and other useless interior bits in the first week of work back in April 2019.

    What we were left with inside was a LOT of floor pan sheet metal covered in this adhesive sound deadening material, which I will refer to henceforth as "tar paper". Its really more complex than that, but tar paper is easier to write. We would fight getting this heavy, sticky, brittle crap out of the BMW for weeks, employing a number of removal techniques. Some here have even called it the Tar Paper Wars. One technique worked better than others...


    We did a cage job back in early 2018 on this EVO X, which had a welded 4-point roll bar we had to cut out and got a proper 6 point roll cage installed in it's place. This car still had all of the tar paper installed, which we had to remove since the entire interior and cage would later be painted grey.

    The method we used to remove this tar paper was suggested by one of our fab guys at the time, Aaron, who had used it successfully on Japanese cars before. The idea is the dry ice gets the adhesive holding the tar paper to the sheet metal so cold that the adhesive breaks loose, and then the tar paper comes off in whole sheets! I wanted to see this witchcraft in person, so we gave it a go on the EVO.

    With a 5 gallon bucket filled with crushed dry ice, isopropyl alcohol was added to make a chunky slurry that looked like a witches caldron. This slurry was carefully poured onto the top of the tar paper (the flat portions), then was allowed to sit and chill a bit, then light percussion with a hammer or scraper was used...

    It was like magic. This stuff just popped out in whole sheets! I never would have believed it, but damn, the results were real. In this EVO. That one time... on that one car.


    We had high hopes and bought two 8 pound blocks of dry ice and a butt load of isopropyl alcohol to try this again on our E46 BMW's floors.

    At first we tried a twist - putting the dry ice + alcohol slurry into a black trash bag, that could let us re-use the stuff in several sections, as well as the vertical paper applied at the front firewall, transmission tunnel, and back seat shelf around the fuel tank.

    Well we gave up quickly on the trash bag, as it did not work at all. We went to straight dry ice + alcohol applied directly to the tar paper, as we did on the EVO. Problem was it was not working well on this car. Not at all.

    We tried this method again another work night, with two more blocks of ice and more alcohol. And more "percussive" persuasion. After many hours over two work nights, $100 worth of dry ice and alcohol, we barely had the passenger and driver seat flat floor sections done, and it looks like a 12 year old's patchy beard. This just did not work on this BMW, maybe due to more advanced age or possibly different tar/adhesive materials the Germans used? I give this a solid FAIL rating.

    I can NOT recommend this method to be used on a BMW. Not to mention that the alcohol poured out of the many plugged drain holes in the floor and trashed my new polished & coated concrete floors. I was less than happy about this - the alcohol/dry ice method is now banned in my shop.


    We were still fighting this battle weeks later, and on the 3rd work night attempt to remove the tar paper, I insisted on trying my old proven method that we have used on dozens of BMWs in the past - a heat gun + scraper.

    This worked so much better on this car. With heat applied to a small section of tar paper for a number of seconds, a 1.5" wide putty knife was used as a scraper, and this stuff peeled right off. Not in entire sheets like on the EVO, but in manageable chunks and in a timely manner.

    The work went much faster than the dry ice, and no hammering was involved, just gentle scraping. It was like peeling fondant frosting off a wedding cake... came off in long chunks, after the heat nuked the adhesive.

    The video above shows this heat technique used on some vertical sections of the transmission tunnel - which would be nearly impossible to do with dry ice, even if it even worked. Like all methods, this still leaves an adhesive residue behind, which we cleaned up on other work nights.

    Tim tried a number of adhesive removers, from Acetone, to Goof Off Pro Strength, Brake Parts Cleaner, and finally Mineral Spirits/Paint Thinner. The Goof Off worked well enough, but its $15/gallon. The cheaper $7/gallon Mineral Spirits / Paint Thinner worked the best - just apply liberally to a blue shop paper towel, wipe it onto the adhesive, use some elbow grease, and the brown stuff comes off. Sometimes it took some work with a red ScotchBrite pad soaked in the same stuff as well.

    I wouldn't call this adhesive removal step "easy" by any stretch of the imagination - its not a "spray on / wipe off" kind of effort. You gotta get in there, use some pressure, and a lot of heavy duty paper towels and a little ScotchBrite to get it off. Just takes time.

    And sure, we could have used some power tools and abrasive discs or wire wheels, but that would have made a giant mess and we would have to prime the floors to prevent them from rusting before the interior is painted (after the cage is installed). I have heard from others that blasting or sanding this stuff only turns it into a fine mist of tar, which re-applies itself to the floorpan and other areas. As well as all over you and your shop. This heated peel + paint thinner method keeps the stock paint/primer clean and intact on the inside. We will just remove the paint near the "mounting feet" of the roll cage.


    Once we had the tar paper out it was a good time to stop and power wash the chassis, while it still could be rolled outside. On one of the work nights (during the middle of the "tar paper wars" above) we rolled the E46 outside and pressure washed everything.

    Under hood, inside the cabin and trunk, exterior - all the things.

    As you can see below, this is with some of the "rear seat" deck structure is removed.

    So much nicer working on a car that has the stinky interior removed, grease and other nasty "road funk" washed out.


    The two ways we have shown have varying degrees of success, and the dry ice method is very hit or miss. We used the same technique on this BMW that worked SO well on the eVO X, and it just sucked. Maybe it is a chemical make-up of the tar or adhesive on the Mitsubishi, but it was a bust on the BMW.

    HEAT + patience always works. There is no mess, less danger, and no cumbersome chore or expense of finding dry ice.

    Thanks for reading!
    Last edited by Fair!; 04-09-2020, 06:24 PM.
    Terry Fair -
    2018 GT / S550 Dev + 2013 FR-S / 86 Dev + 2011 GT / S197 Dev + C4 Corvette Dev
    EVO X Dev + 2007 Z06 / C6 Dev + BMW E46 Dev + C5 Corvette Dev