Sorry is this is the wrong forum. Has any one ever experienced mold fungus growing from grout? I'll get some pics up this afternoon. I have 2 fireplaces in my home. The one in the basement (the one at issue) sits directly below the one on the upper floor and has never been used since I have owned the home. They share a chimney but not a flue. The fireplace masonry has been painted. I have a few grout lines that are getting a white chalky growth that is bubbling the paint and coming through the paint in a few areas. Like the grout is sluffing and turning to powder. I can't tell if this is a result of a poor regrout job or is a fungus. Nothing is damp or wet and it is only happening on 4 or 5 grout lines. I was going to scrape it off and apply a bleach solution to it and see if it cures it but I have never seen this before.