I would frist try a simple cleaning with a heavy duty cleaner. If there are any stains after that perhaps a Hydrogen peroxide poultice

On Thu, Nov 5, 2015 at 7:45 PM, <csantospago@gmail.com> wrote:
Hi Partners,

This commercial building in Boston just went through an exterior renovation. After the cleanup they noticed staining on these granite steps and part of the walls.
Not sure what it is.  Any ideas on how to approach this?

Thank you, Chris


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