The tile will crack off! You can't use thinset on the liner. You need a new drain to connect to the liner. Then, you need 1-1/2" or so thick setting bed that you could then attach the tile to. WIthout redoing the curb, it would be too low.
You're much better off trashing the whole thing and building it per one of the approved methods. While you're taking the rest apart, you may want to check out the drain and trap - if they're cast iron verses say pvc or abs, they may need repair or replacement.