What would you do to fix this shower? Very bad soap scum. Stonetech Restore mixed medium and then strong strength took off a little but not nearly enough.
Most soaps for cleaning are alkaline on the pH scale. Restore is an acid that's why you've had little success. Try an alkaline product. Having said that, it's gonna be tough! All that build up on the verticles and no real means for dwell time. Pioneer eclipse makes a gel stripper for base molds. Dwell time is always important on nasty jobs.
So, baseboard stripper on a slate shower? I would have never thought of that, but makes sense. Clean that up and then try on the rest with an acid. I'm in.