After my frescos are finished, dried, etc., I notice they cannot get wet; the pigment will smear...In fact, the putty will soak up a lot of moisture and get soft. Doesn't the pigment and putty turn to stone and become impermeable? Is there a curing time for a finished fresco in which it will turn to stone. My friend wants me to make fresco tiles as part of the splash board behind her sink in the kitchen. Aren't there frescoes outdoors on the sides of cathedrals and the like?