I have a beautiful but probably impractical natural slate tile on the floor and walls of my bathroom, including the shower.
The shower floor has stains on it that seem to be beyond soap scum, perhaps lime or hard water stains.
What would you recommend for cleaning it before re-sealing?
Thanks for posting a picture, as this helps me tremendously to understand your problem.
Unfortunately, I see this problem almost every time we see slate tile in a shower location.
You can try a few different things before re-sealing.
First you can try cleaning the best you can with a soap-scum remover and a razor blade.
It looks like it could be some soap scum and calcium build up.
This is how we attack the cleaning, with varied results.
Remember the sealer will not last very long in such a wet setting, so it will have to be done more often than you think.
One thing I also see in the photo, is the slate seems to be shiny. Is there coating on the slate tile?
If so, this could be even more challenging than just a cleaning.
To re-coat your slate tile, you may need to strip the coating.
Not sure what's going on exactly, but if there is coating on it, then maybe more challenges await you.
I wish I could be more help, but slate tile should not be in a shower and any coating should not be on any natural stone.
Always use penetrating sealers and if you want some finish, use a color enhancer sealer to darken the stone.
Thanks for your advice. The shine is, I think, from the original sealer used on the stone.
The sealer appears to have worn away from the edges in on some of the tiles, leaving the white marks you see.
We will try a soap scum remover, as you suggest. Would something like CLR do us any good, or is that a no-no?
You can try CLR, as it does cut soap scum. As I said before, the sealer that was there before is a coating and is starting to wear off the stone.
This is where your challenges will begin. What you need to find out is what coating was used so you can re-coat using the same product.
Or, if you don't re-coat, you will need to strip, which can be challenging.
You will need to make the call. Usually CLR will not break down the coating, but will help with the soap scum.