I finished grouting my new bathroom tiles a weeks ago. I have noticed when I wipe the tile down with a damp cloth the grout darkens as if it has absorbed water. The grout is Bal superflex colour limestone. I have since applied two coats of Fila grout protector. But the grout still discolours when wet. Do I need to apply a waterproofing agent or is this normal. I do not want to start using the shower until I am sure the grout is waterproof.