The work on the undercarriage continues now after the problems I had last fall. As the new paint did not stick to the undercarriage at all, I have to redo the entire project I started in the fall of 2015 once again. The car already looked fantastic when I found out that I have a problem. The paint shop wanted to have the undercarriage media blasted this time, to make sure that everything is 100% clean, and that the paint can stick to the metal much better due to a rough surface.
Personally I´m not a big fan of media blasting a non disassembled car, as so many things could go wrong and I do not recommend to do it to anybody else. The paint shop really wanted to go this route though, and they said that they have a very experienced media blaster to perform the work. They did tape the car for hours to make sure that the blasting media would not go close to any mechanical or fragile parts. The blaster worked with very low pressure (1bar - 14psi) to get the old paint off and it really came off within minutes. He did not want to risk anything and so there were some areas with the old paint left after he was finished.
We then spent a whole day trying to get rid of the rest of the remaining paint, by hand. With 240 grit paper we worked on all the areas we could reach. After a whole day under the car it was clear that we could not reach all the areas and that the job would not be good enough.
I then contacted a dry ice blaster who took over to remove the rest of the remaining paint. Normally you cannot remove paint with dry ice blasting, but as the paint on my car´s undercarriage does not stick, it works. It took him a couple of hours to get everything off. The undercarriage is now completely clean and back to bare metal once again. He even was able to remove some of the old undercoating in the rear wheel wells which the other dry ice blaster could not get off.
We will now degrease everything multiple times and then scuff all the metal. Then its time to mask all the necessary parts and repaint everything once again with 2k paint. I will keep you updated here on my website about the progress.
The media blaster at work Media blasting the undercarriage. The bare metal wheel housing after blasting. The rest of the paint was removed later by hand and by dry ice cleaning. After blasting Ready for dry ice cleaning. The dry ice cleaner managed to get the last undercoating out of the rear wheel housings. Dry ice cleaning Everything is perfectly clean now. All the suspension parts were perfectly cleaned as well.
I´m restoring the undercarriage of my 1974 Cadillac Coupe DeVille. See below. As I want to do it as perfectly as possible, I wanted to remove all the undercoating which was applied when the car was new. I do not like rubberized undercoating, as you cannot see whats going on underneath. It can trap moisture and once it flakes off due to corrosion, there is already some major damage in the metal underneath.
There are different methods for removing the undercoating and most of the methods are a pain in the a**. This stuff can be removed with a scraper and chemicals, or with heat and a scraper. Both methods will damage the metal underneath and scratch the paint on the underbody, and it takes forever…
As I did not want to use any of the methods mentioned above, I decided that I wanted to try dry ice blasting.
Dry ice-blasting is a form of carbon dioxide cleaning, where dry ice, the solid form of carbon dioxide, is accelerated in a pressurized air stream and directed at a surface in order to clean it. An alternative media for non-abrasive blasting is water-ice, known as ice blasting. The method is similar to other forms of abrasive blasting such as sand blasting, plastic bead blasting, or soda blasting but substitutes dry ice as the blasting medium. Dry-ice blasting leaves no chemical residue as dry ice sublimates at room temperature. Dry-ice blasting involves propelling pellets at extremely high speeds. The actual dry-ice pellets are quite soft, and much less dense than other media used in blast-cleaning (i.e. sand or plastic pellets). Upon impact, the pellet sublimates almost immediately, transferring minimal kinetic energy to the surface on impact and producing minimal abrasion. The sublimation process absorbs a large volume of heat from the surface, producing shear stresses due to thermal shock. This is assumed to improve cleaning as the top layer of dirt or contaminant is expected to transfer more heat than the underlying substrate and flake off more easily. The efficiency and effectiveness of this process depends on the thermal conductivity of the substrate and contaminant. The rapid change in state from solid to gas also causes microscopic shock waves, which are also thought to assist in removing the contaminant.
Unlike abrasive media blasting you can not remove rust with dry ice blasting.
I found a company through the website of a classic car club, which is only a little over an hour away. I wanted to have it done before the first snow and as soon as possible, so that I could continue working on my car during the winter. The owner of the company did a great job. He is a very friendly and competent gentleman and it was a pleasure working with him. Here is a short video how it was done: (make sure to watch in HD for proper image quality)
The car was lifted with a forklift and then covered in plastic.
One of the rear wheel-housings before blasting - you can see the undercoating everywhere. The same wheel housing after blasting - all the original paint was still very well preserved under the undercoating. As you can see originally the wheel housing was brown. During painting a lot of overspray from the body landed in the wheel housing. Then Cadillac added rubberized undercoating to protect the metal from stone chips and to keep the car more quiet. Luckily there is no rust to be found anywhere. During blasting. The original brown paint showed up underneath the undercoating. The paint is still in perfect condition.
The original paint showed up underneath the undercoating in the wheel housings as well. After cleaning - it came out really nice! I will touch up some areas and conserve the others with a special transparent coating. I´m very happy with the result of the cleaning and will now have to protect everything and paint some areas.