HI, We just had a bluestone patio installed next to our house. We had two days of heavy rain, and the mortar between the stones went from cement colored to brown/dark brown...What could cause this? The grout is no longer wet. I have contacted our contractor who is quite reputable. The grout also seems to be creeping onto the stone giving the geometric shapes an uneven/wobbly appearance. It's not pretty...Any thoughts?