I can be rather more positive about the SPL process than some of the posts above. I had my 3500S base unit and panels chemically stripped, cleaned and electrophoretically (E-coat) primed back in 2012. I found their service and process to be excellent, and would have no hesitation in recommending it - BUT as Colin says, you have to apply some of the laws of physics to your expectations. At no point did they guarantee to me that all rust would be removed from folded edges like door skin edge seams, and spot welded lap joints in panels. It would be impossible to get their solutions into such places without opening up the seams slightly, which to be fair I did with a small flat chisel in such areas where I could see rust had formed.
I did an awful lot of research into the process before I committed to it, including a visit to their works. It is not a simple acid dip, the shells and panels go through a multi stage immersion process which removes different elements at different stages. The later stages remove rust with no erosion of the parent steel, and the final stage is a neutralising bath which will deal with any corrosive residue left behind, and leave the surface clean enough to paint. The primer E-coat is an optional additional process and is not applied at their site, but is only available through them. My P6 base unit and panels were sent to an MoD contractor in Mildenhall to be done, but I know that facility has since closed. The last shells I have had done were E-coated at GKN on the Land Rover chassis line in Shropshire. It is worth remembering that the E-coat process also involves eight immersion tanks, six to remove all possible contaminants, the last two being full of the special PPG primer containing £450'000 of the stuff, according to the site manager, so they have to be absolutely sure that anything going into it is free from any contamination.
It's worth mentioning that SPL recommend that a shell is fully cleaned by them first, then returned to you for repair, and then back to them to be cleaned again and E-coated. This is ideal as once the shell is clean all rusty areas can be clearly seen, and the steel is so clean it welds like brand new sheet. In my case, I couldn't afford the extra cost, so opted to repair my base unit first, then have it stripped, cleaned and E-coated in one hit, which with the exception of some totally unexpected perforation in the boot floor, worked out well for me.
As I said, I have personally found them to be very proffesional in what they do. There is no other process which even comes close to theirs for comprehensively removing rust and other contaminants from difficult to access areas like inside box sections, and protecting these areas again afterwards. I would say it's as close to a factory new finish as can be achieved today on an old body shell. I had heard all the stories referred to above, like handling damage and shells hanging about their site for ages, but I didn't see any of that. My P6 base unit was handled very carefully, and compared to some of the exotica they had in, was of very low comparable value. There is quite a long waiting list for their process, it was about five months when I last used them on another project last year, and once shells are booked in they are generally turned around in about two weeks. They do not have the capacity to store shells for long due to the amount of them that they are processing at one given time, so only give a few days grace for collection when completed.
If anyone is interested I will dig out the photos of my P6 base unit when it was done.
