| Yes you can tile over tiles but only once. If the existing tiles are shiny score them with a tile scribe or angle grinder for better adhesion. You can also use a latex addative that can be mixed in with the floor adhesive. The laytex is used when laying tiles on wooden surfaces such as upstairs wooden floors in bathrooms for flexability, it also makes the adhesive very sticky when mixed. Ihave tiled over many floors using it and did not have to score the existing tiles underneath. Scoring is cheaper, laytex is cleaner |