Wet white marble shower floor turned gray!
During my bathroom remodel, I had Green Ming Basket Weave mosaic marble installed on shower floor. The pan was properly installed w/Portland cement, cured for a few weeks before mastic & tile was layed down. The white marble looked beautiful for weeks. I believe it may be thassos marble. After the plumber turned the water on, the tile darkened to a soft gray. After weeks, the outer areas of the floor returned to white color but the center area is still gray. I used a heat gun on a few tiles, they turned white but the next day they were gray. Could this be a moisture problem? We have tried blowing a space heater over the floor for 2 days, but no change. Has anyone had a similar problem? Thanks.