I think it is the grout . maybe there is no moisture barrier and the grout being the weakest point is releasing ( due to vapor transmission) the pigment from the grout into the absorbent rough cut edge of the limestone staining it. Its a small area so maybe you could remove all the grout down to the thinset.Then let it dry and find a poultice to place into all the joints easily removing the stain. Ok I was just kidding about easily removing the stain but I didnt know how else to finish the sentence. If you can find a poultice to actually do this you would have to vacuum it out. I may know a company that could formulate such a poultice I will check it out if you are interested.Then you could fill the grout lines with a epoxy or urethane type grout. It would probably be better to replace the 100 sq ft with another product by the time this all got done. 

 
On Fri, Sep 24, 2010 at 11:46 AM, <info@restoreyourtiles.com> wrote:
Maybe the grout stains the stone?

Sent via BlackBerry from T-Mobile

From: "info @surfaceshawaii.com" <info@surfaceshawaii.com>
Date: Fri, 24 Sep 2010 05:34:27 -1000
To: Restoration and Maintenance<sccpartners@stoneandtilepros.com>
ReplyTo: "Restoration and Maintenance" <sccpartners@stoneandtilepros.com>
Subject: RE: [sccpartners] Dark brown stains on limestone

I don't have any idea what the staining is but I have seen it happen on the same type of stone that has been sitting in a shipping crate, left out in the weather and this had occurred prior to installation. I had thought it was some sort of brown manganese staining but not sure. They ended up removing the stone and the stain does not go all the way through, it is just about 1/16 - 1/8 beneath the surface and only along the grout joints. I am pretty sure it involves moisture that is reacting with some type of mineral in the stone, but what I don't understand is that the grout also has the staining all the way through.

Thanks 

On Fri, Sep 24, 2010 at 12:32 AM, Fred Hueston <fhueston@gmail.com> wrote:
Rule number one in stain removal....ID the stain. you have any idea what the stain is, once you do than you can apply a poultice or the new Stain Sponge

On Fri, Sep 24, 2010 at 2:51 AM, Stephen Webb <stephen@newlifemarblerestoration.com> wrote:
Greg, maybe try a diluted ammonia poultice. I've seen similar stains and had some success.
----- Original Message -----
Sent: Thursday, September 23, 2010 2:38 PM
Subject: RE: [sccpartners] Dark brown stains on limestone

the area is outside, about 100 sqft and I have tried just about every form of acid or flouride cleaner, and even mold cleaners. What seemed to work the best are the acids, but they just etch off what is on the surface and whats in the picture is what is left over. Also tried grinding but to no avail. The only thing I can think of trying next is some form of poultice.
fiAny ideas?

thanks

On Thu, Sep 23, 2010 at 2:21 PM, <info@restoreyourtiles.com> wrote:
You need to include more info like is this inside or outside, how big is the stained area, possible orgin etc...

Sent via BlackBerry from T-Mobile

-----Original Message-----
From: Greg Cook <info@surfaceshawaii.com>
Date: Thu, 23 Sep 2010 11:29:00
To: Restoration and Maintenance<sccpartners@stoneandtilepros.com>
Reply-To:"Restoration and Maintenance" <sccpartners@stoneandtilepros.com>
Subject: [sccpartners] Dark brown stains on limestone

Does anyone know if these stains can be removed?

Kindly,
Greg Cook
surfaceshawaii.com
808.891.1963

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Surface Solutions Inc.
808.891.1963

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Frederick M. Hueston PhD
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www.stoneandtilepros.com
Recommended stone care products  http://www.stonecarecentral.com/?Click=2149

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Greg Cook
Surface Solutions Inc.
808.891.1963

See what our clients are saying about us  http://www.surfaceshawaii.com/what-our-clients-are-saying.html

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Regards,
Stu Rosen
201-446-1200
www.mbstonecare.com
www.stoneshine.com
"A posse ad esse "