removing mineral (rust-like) stains from slate and grout [Archive] - Ceramic Tile Advice Forums - John Bridge Ceramic Tile


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bobby brooks
04-26-2004, 02:40 PM
Is there a product that will get mineral stains (rust-like) off of slate and the grout between the slate tiles? Nothing I've tried to date has made any impact at all. Thank you.

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04-26-2004, 07:21 PM
Hi Bobby, Welcome! :)

What kind of slate do you have?

What kind/color of grout did you use?

What have you tried to clean it with?

bobby brooks
04-27-2004, 11:29 AM
John: This slate was installed about 4 1/2 years ago by a local area contractor who came up from Nogales, Mexico.

I'm not sure what kind of slate it is -- it came from Mexico and a friend thinks it is called cantera.

The grout is a light gray in color and I don't know what kind of grout it is.

At the suggestion of my neighborhood hardware store, I tried a Clorox bleach pen and then, when that made no dent, I they recommended CLR -- again, no dent.

Hence, my internet search for help.


Michael Meyer
04-27-2004, 12:43 PM
Hi bobby sorry to give you some bad news, I think your iron oxide may be permanent. Iron oxide staining is difficult to impossible to remove even in an optimum condition, however when sodium hypochlorite (bleach) is used the rust like staining becomes permanent. Sorry:( Michael of Stonehenge

Steven Hauser
04-27-2004, 12:57 PM
Hi Bobby,

The other potential is that the rust like stains are actually Pyrite. If that is the case then it too is permanent. Many slates and quartzites contain pyrite.



bobby brooks
04-27-2004, 06:42 PM
Michael and Steven: Thanks for your responses. I only tried the bleach on a very small section of the grout -- so, that is the only area that will be permanent for that reason. Any other thoughts on things to try? Also, still want to seal. I have this slate in different shower areas. Thank you.

04-28-2004, 07:36 PM

In the marine industry we use Oxalic acid in a gelled format to remove severe rust stains from gelcoat (very effective). Would this have any chance of working on these slate/iron oxide stains? [Realizing full well that in time they will most likely reappear]

John Bridge
04-29-2004, 05:22 AM
No stone expert here, but I would imagine the "rust" is emitting from the stone. I don't think it's going to go away. And in a shower?

Maurizio Bertoli
04-29-2004, 06:00 AM
You're damn straight, JB!
Cantera stone is one of the crappiest stone on earth! 4 1/2 years installed? I believe it's world record!! All others got rid of it much sooner!! ;) :(
But, oh, I forgot ... you're going to seal it ...
Oh well ... then everything is going to be all right!!;) :shades:
(Yeah, right!!)
Ciao and good luck,