The floor and shower walls are now starting to stain and turn white. How can I clean them?
That white film may just be soap scum.
The reason why phosphoric acid is the most commonly used active ingredient in bathroom cleaners is that it will cut through soap scum like a hot knife through butter, but won't attack chrome plating.
So, buy any phosphoric acid based bathroom cleaner or toilet bowl cleaner and see if it cleans the white film off your bathroom slate floors and walls. Bathroom cleaners will typically have about a 5 to 10 percent phosphoric acid content, whereas phosphoric acid toilet bowl cleaners will typically be 15 o 20 percent phosphoric acid. So, you need to be a bit more cautious using a toilet bowl cleaner, especially on any unsealed grout. 20 percent phosphoric acid will eat your grout, so maybe dilute it with water a bit. Also, the toilet bowl cleaner will be gelled so that it sticks to surfaces better.
I'd check to see if phosphoric acid removes the white discolouration from your slate, and if so, it's probably soap scum and any bathroom cleaner will remove it.
And then what is the best product to seal with?
To seal the slate, I'd probably phone up the places listed under "Janitorial Equipment & Supplies" in your yellow pages phone directory and find out who sells "Johnson Professional" or "S.C. Johnson Wax" products. Anyone carrying either one will know the local Johnson Wax sales rep, and he'd be the first person I'd turn to for advice on what acrylic sealer to use to seal a slate floor.
Johnson Wax is well respected in the janitorial business because they make good sealers and finishes for commercial flooring like vinyl composition tile floors (many janitorial service companies make much of their income maintaining VCT tile floors). And, they train their sales representatives well. I'd ask for the name and phone number of the local S. C. Johnson sales rep, and go with his recommendation.
There are two different kinds of acrylic sealers. Sealers that form a waterproof film over the masonary are called "film forming sealers". Sealers that penetrate into the masonary and occupy all the highest capillary pressure sites, and then harden up in those locations are called "penetrating sealers". In my view, it's best to have a film forming sealer on the walls of a shower so that you can clean that shower with an acidic cleaner to remove the soap scum without harming the grout, but to have a penetrating sealer on the floor of a shower or bathroom so that the floor isn't slippery when wet. Similarily, you want to use a film forming sealer on kitchen floors and on counter tops where soft food would otherwise get mooshed into porous grout and provide a food source for bacteria.
I don't know if Johnson Wax makes a penetrating sealer for masonary floors. I do know that "Technique" is an excellent sealer for vinyl composition tile floors, but it works by forming an impermeable film, and wouldn't be appropriate to use on a bathroom or shower floor because it would make the floor very slippery when wet.
If you can't get hold of the S. C. Johnson Wax sales rep, you might want to try using Tile Lab "Gloss" Sealer & Finish on your slate bathroom walls and Tile Lab "Matte" Sealer & Finish on ONLY the bathroom floor grout lines (not the slate itself) which are available at Home Depot. The reason why I'm suggesting these two products is that they can both be easily removed using Tile Lab's "Heavy Duty Grout Cleaner & Stripper". Both sealers stick to the grout well and last a long time, but one advantage is that they're easy to remove should you want to.
Also, if you're going to use the Tile Lab Gloss or Matte sealers, be sure to give the walls and floors a good cleaning with a phosphoric acid based cleaner to remove any soap scum first. The reason for this is that mildew feed on the vegetable oils that bar soaps are made from, and so soap scum represents a food source for mildew as well. If you put a sealer over soap scum, you can have mildew feeding on that soap scum under the sealer. So, a good cleaning to remove that soap scum first is in order, and having the ability to remove the sealer where you might see mildew growing under it is also in order. Mildew will never grow on clean grout under a sealer because, just like everything else, it needs food to survive.
