I replaced 3 broken tiles 4"x4" tumble stone, and in the process decided to regrout entire shower stall. I removed grout and in some areas there was like a build up of either calcium deposits or lime or soap scum very hard. I actually had to used my Dremmel tool to remove the build up. I removed probably around a 1/4" of grout all around, regrouted entire shower stall and waited 72hrs. When I came back I noticed that grout had dry darker in some areas and light in others. The grout is Linen color it has to dry light not dark brown.