Originally Posted by
JazMan
You can't waterproof grout, but you can apply a sealer which slows penetration and makes cleaning easier. Any waterproofing required is done before the tiles are installed by the use of membrane either sheet or liquid.
I disagree with ballenger about installing new tile over old tiled floors in good condition. It can and is done with good results. The old floor must be in good shape and solid with not loose tiles, cracked or missing grout which would indicate movement in the substrate. Clean the floor, abrade using a carborundum rub stone or belt sander. Use a high quality modified thin set that states it's OK for that purpose.
You say the floor is lower than the rest of the floors. That's kinda unusual, why is that? Do you know how the tiles were installed...the method I mean? Is it original, how long has it been in place?
Jaz