My mason laid a bluestone porch and when he grouted with portland the grout left stains around the perimeter. I dont want him to clean it with muriatic acid as he suggested. Another mason said to use a floor polisher with a nylon abrasive pad and a solution of water and ammonia 16:1, and then a color impregnator #511(?). What is the best solution?

 

Dear Rob:

Without actually seeing your installation I can't tell for sure. You're making reference to staining, but are we actually looking at a discoloration, or only a residue of grout film sitting on top of the stone?

It is quite possible that it is a film residue and, if we have to go by that assumption, the words natural stone and acid (especially Muriatic!) should never appear in the same sentence. Water and ammonia? I never ever heard that ammonia could remove grout film and I actually highly doubt that it would. I'd rather consider using a specialized heavy-duty alkaline cleaning agent with chelates in its formula like MB-3 with a floor machine and a scrubbing brush instead of a nylon pad; the nylon pads would get shredded pretty quickly – not to mention that is not as effective as a scrubbing brush. MB-3 is indeed very effective and is rated “for natural stone”.

Finally as for the sealer, it is never a good idea to apply an impregnating sealer to stone installed outdoors.

May I ask you now to please read and e-sign our Statement of Purpose at: http://www.marblecleaning.org/purpose.htm?

Ciao and good luck,

Mauri z io Bertoli

 

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