Got this email some suggestions on cause and a remedy
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Begin forwarded message:
I am sendding you some pictures.
this projecctwas done in mid March. Mason told us that these stains will disappear as it is caused by moisture absobed by stone . we have been waitng for. five months with not much luck. He thinks is caused by alkaline staining.
I wonder if there some way to remove these stains. He is suggesstig paiting the fireplace.
Thanks for your very prompt response