Here are a couple of points to help - further to what has already been said. 1.) To get old tile adhesive off the back of tiles that you wish to reuse, then soak them for 2-3 days totally submerged in water. This leads to the second point. 2.) Make sure that any bathroom is well ventilated, as if moisture has no where to go then it will travel through the grout lines. When buying grout and adhesive people make the mistake of buying "water resistant products" rather than "water proof". 90% of grouts and adhesives are water resistant - what this essentially means is that water won't damage or