Years ago, acid dipping automobiles was confined to race cars. Leaving a car's body or parts in an acid tank would eat away the metal, making it thinner. The longer in the tank, the thinner the metal. This would mean a lighter car, and with racecars--lighter is quicker. Today the materials have improved but the process is very much the same.
Now, when using the stripping, acid dipping procedure associated with high-quality restorations, it is arguably the best process for a durable foundation for any renovation. Upon completion of this procedure, the client has a body free of all paint, body fillers, seam sealers, undercoat, and most importantly rust. You have a clean slate (although there are probably a few more holes than anticipated). It is by no means inexpensive; an average-sized body with the previously attached sheet metal will cost $4500.00 give or take. But when you are doing a higher-end restoration this constitutes a minor expense and is money well spent.
Whether performing the restoration yourself or sending it to professionals, the car must be completely disassembled. For the vehicle to be completely apart, bodies must be separated from the frame, all suspension parts removed, no wood parts, any aluminum pieces removed--vin tags and the like must come off. Only steel parts go in the tanks.
The vehicle is attached to a jig or cage to allow controlled movement in and out of the 3 tanks used in the process. At this point the project vehicle is immersed in the Hot Tank. The stripper in this tank has an average temperature of 200 degrees. After a 2-day bath, the vehicle is removed, pressure washed and examined. If the vehicle had a minimal amount of paint, body filler and undercoat, 2 days may be sufficient. If there remains unwanted debris on the body, this will require scraping to loosen any residual materials. The vehicle again goes into the tank and the process is repeated. In rare instances, the vehicle may have to go in a third time to remove everything. When the employee is satisfied it is as clean as possible, it goes to the acid tank.
The project is now lowered into the acid tank. The tank is filled with Phosphoric Acid which is most caustic. Only one day is needed to remove years of oxidation and any unwanted materials. What we are attempting to produce is a clean rust-free vehicle--one day should be enough time to accomplish this. The project is again pressure washed, as it is after removal from all tanks and moved to tank 3.
The body and/or parts are now dipped in the last tank, which is filled with a neutralizer, and rust-inhibiter solution. The process removes residual acid, and anything else remaining from the acid bath. It cleans the body and parts inside and out. A good pressure wash and air dry completes the process, with no residue left to leech out of joints and seams, ruining what would have been a great paint job.
A rust-inhibitor allows time to transport the vehicle and put it in prime. How long is the coating effective? There is no definitive answer on that, however, the project should not get wet. It should be prepared as quickly as possible for prime. A car sitting in a garage in arid Arizona is likely to remain rust free longer than one sitting in a damp garage in Louisiana.
When the vehicle is received and ready for prime it should be Scotch Padded with a mineral spirit solution and dried to remove the rust inhibitor. At this point wipe with a solvent-based wax and grease remover, blow off, tack and prime. A good corrosion resistant epoxy prime is recommended. The cost of good quality paint materials is not an area to attempt to pinch pennies. Inferior products are not a savings when the project may need to be stripped down to bare metal and redone.
The vehicle is now ready to go to the body shop for metal work. There are protective coatings necessary for inaccessible areas, but that should be done after body work and paint completion and before assembly.
There are numerous other methods of getting a vehicle down to bare metal. I personally had a couple of hoods sandblasted and upon receiving them, I walked the parts straight to the dumpster. I'm not saying that another media may not have been a little gentler or if the blasting company's employee more knowledgeable the outcome might have been different, but this process can't remove what can't be seen. Dipping cleans vehicles inside and out, gets to every crevice and is a safe way to remove everything. Again, it is necessary to apply protective coatings to all areas not accessible to primer and paint applications.
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