Acid dipping of the classic Porsche 356 Cabriolet restoration currently undergoing full bare-metal rebuilding here at DSD Motorwerks in Essex has just been completed. The fully exposed metalwork shares some unhappy secrets.
Enthusiasts call this paint strip process acid dipping, but no acid is used on the bodyshell. Our preferred method uses an alkaline solution to remove surface contaminants including paint, but only after the bodyshell has been heated, or baked using the pyrolysis to lift much of what is attached to the metalwork.
One objection often raised against acid dipping is that some stripping solution may be trapped in the body seams and leak out when the car is being painted. On a shell with this many holes that is highly unlikely but, even on good shells, the stripping solution is completely drained from the bodyshell before the entire shell is two-pack etch primed for maximum rust resistance.
While these concerns are the main objections to the process, the major benefits of this process far outweigh any issues. Media blasting will heat and distort metal – especially wafer-thin rusty metal – until it is completely mis-shaped and no longer usable. It also fires a lot of sand or soda into body seams and crevices at incredibly high pressure: that material will be coming out of the car for years afterward.
Acid dipping can also get into crevices that no sand blaster could ever hope to get to, flushing out issues and giving a clean surface for primers and body wax to flow through. It is important to make sure maximum access is available into all closed body sections for the fluid to do its best work by drilling access holes, or removing parts of chassis box sections for later refitting.
There is some debate over how body lead is affected by dipping (it is normally removed), but with the depth of restoration normally undertaken on our classic Porsche projects, that is a non-issue for the DSD Motorwerks team. DSD can add new lead later on if the job calls for it, but we can also afford to take more time than the factory had to get the bare metal right in the first place.
Take a look at these photos to see the extent of the rust and corrosion on our Porsche 356 Cabriolet restoration. Rest assured that we will make it as good if not better than new! Contact DSD Motorwerks to discuss your classic Porsche 356 project today: these cars are wonderful. Thankfully, their increasing value nowadays makes them well worth saving.