i am looking for a person or a product that can remove many many years of hard water deposits from a large slate shower (it is not a tub enclosure) - almost like a small room.
I suggest this experiment. When Zest soap first came out many decades ago, it advertised that it left no bathtub ring in hard water.
Suggestion: Buy one bar of zest soap, and made some very soapy water with it, and see if it dissolves your hard water deposits.
If it works, then let us know, so we can recommend it to others.
If it doesn't work, then let everyone know to not recommend it to others.
Kermit Rose < firstname.lastname@example.org >
Kermit, you're funny.
I concur with the white vinegar approach. The thing about vinegar is that its acid property is fairly weak and its effectiveness wears off quickly. In order to keep it on the job longer, I soak a small sponge or cloth in vinegar and let it sit on top of the offending deposits overnight. If it won't come off with a little scratch with a fingernail the next morning, squeeze out the old vinegar and add some more. Keep after it if the deposits are really thick.
I've tried Lime Away and a dozen similar products and they are all toxic and don't work any better than vinegar. Some of them play Hel with septic systems too.
You can buy gallon jugs of white vinegar at Costco pretty cheap.
Let us know how it goes.