The question about the best way to remove sound deadening material comes up quite frequently on several web forums I frequent. I thought I’d jot down some thoughts and what’s worked for me in the past.
Always wear protective clothing. Be sure to wear face & eye protection, ear plugs, long sleeved shirt, no open toes and gloves.
The best method is liquid nitrogen, but it’s a little more involved for the occasional build. First, you have to find a place that carries it (welding gas supply is your best bet). Second, you’ll need a wand to apply it which is a little more involved than most people want to get. The Liquid Nitrogen process has been known to take a 40 hour process and turn it into 4 hours with beer breaks. It will even freeze the seam sealer. Hit it with a chipping hammer and watch it shatter. KA-Pow… !
If you live in a warmer climate, dry ice is the next best thing. It is available several places -ice cream shops, grocery stores etc. You can get it for .17 to .25 per pound at ice companies. Look them up in the phonebook/online. The best trick I’ve come up with is to put it in plastic grocery bags, and crush it up a little so it conforms to the contour of the floor. Let it sit for about 10 minutes or until the underside is frosted over. Move the bags to the next area that you’ll want to clean and hit the frozen section with a hammer. I’ve had better success with a sharper edged hammer over a dead blow type hammer. Even better results with a welding/chipping hammer or an air chisel. Once the area is clear, move the bags again and do the next section. The bags will help keep the undercoating pieces out of the ice and makes cleanup easier. To do vertical sections takes a little creativity with duct tape, magnets or simply stacking the bags upon each other.
Cold climates have an advantage. The stuff sometimes just pops right off w/o much work.
Heat/Scraper. Depending on the chassis, one way will work better than another. Always try chisseling it out “cold” first. You’ll sometimes get lucky and have some bigger sections pop loose. Once you heat it, none of it will just pop off anymore.
What you can’t get off with the above methods will need to be wire wheeled. 4″-4.5″ grinder and a knotted wire wheel is the best and quickest. 1-1.5″ on a high speed drill or pnuematic die grinder will get the hard to reach stuff. A cup wheel is good to have as well for some corners. The wire wheel will take it down quick, but will leave some residue and will rarely take it all the way down to paint. 3M blackwheels or similar will clean it down to bare metal (for cage pad prep).
Once it’s all chipped/wheeled out, wipe down with mineral spirits to get the remaining residue off. You can go harsher (laquer thinner, aircraft stripper etc), but mineral spirits smells less, less caustic, and cheaper. If you want really clean, wipe down with Acetone or Alcohol.
How much weight can you pull out of a chassis? It really depends on the chassis. Miata’s, maybe 10-12 lbs overall. Higher end BMW’s and Porsches, at least 60lbs if you do the entire car. Remember to think about where the weight is. It’s down low next to the CG. Strip the drivers side front for sure, but think hard about removing it from the PS and rear. That’s good weight when you’re not allowed to ballast the car.