Today I removed the tar undercoating material from the tops of the floorpans. This material is supposed to act as an insulator for sound and heat. It was applied to the bare metal by Nissan prior to painting. I want to get under there as part of my process of fully stripping the body in order to find and neutralize rust.
The two most popular way to remove this stuff are (1) using a heat gun to soften it and then scrape it off and (2) using dry ice to freeze it so it becomes brittle enough to shatter-off. Having used the former method I would highly suggest that anyone else use the latter. It would have probably been faster and less messy to use the dry ice.
Here are a couple of pictures of the undercoating, which was in two sections (front and rear) on each side of the cabin. I began with the rear section on the passenger side. I applied heat to the corner with my Harborfreight heat gun.
When the material started to bubble on the surface, I used a metal scraper to lift it at the corner. I pushed underneath, scraping up the material and moving the heat gun to stay ahead of the scraper.
I opened up both garage doors because the smell was pretty strong. I worked my way across the front edge, and then back along the door opening.
Next I worked across the panels and up the opposite side (front to back) along the transmission tunnel. Then I scraped all in between to remove the bulk of the material.
Then I turned my attention to the front section of undercoating on the passenger side. I started on the floor.
Then I moved up the firewall using the same scraping procedures. It took around 90 minutes to complete the passenger side.
Next I did the driver’s side, which took about another hour.
After the scraping was completed, I moved the body outside. There was still a lot of tar residue remaining on the floorpans because the scraping just removes the bulk of the material. I used a tar-removing solvent known as “Goof Off” to remove the residual tar.
The solvent has some fairly awful fumes and can be tough on skin, so I used my heavy stripping gloves. I poured a bit of the solvent onto the floorpans and then agitated it with my scrub-brush, as recommended in the product instructions.
Then I wiped the residue off using a clean rag. The solvent did an effective job of loosening the remaining tar from the metal but I had to physically remove it by wiping. The solvent was oil-based but tends to evaporate fairly quickly, so it was important to remove the material quickly.
I used the same method on the other side of the car. In no time the bare metal floorpans were exposed. The verdict is good, at least from the top: there is minimal rust around the drainage holes only and the floorpans are largely solid. Here are before and after shots:
The solvent I used was pretty nasty stuff, although effective. For this reason I would recommend trying the dry ice method.
While I was working with the solvent I decided to remove the remaining horsehair padding stuck on the top of the front wheel wells. I applied some Goof Off and then scrubbed the hair and adhesive with my scrub-brush.
That got them pretty clean. I applied a bit more solvent and used a scouring pad to remove any remaining adhesive from the rear shelf and side areas, as well as the wheel wells themselves.
Then I used a wet rag to wipe away any remaining solvent.