I have ten ceramic tiles that buckled between each pair at the grout joint. The tile was adhered to the concrete slab using a thin set mortar adhesive over some sort of a papery material. All ten tiles came off easily and I was able to get up about seven tiles worth of adhesive and whatever the papery stuff is, but the adhesive is tight to the concrete where the other three tiles were. It seems that no amount of chiseling is helping to get this stuff off. Any suggestions? I can't put down the replacement tile until I can get this thin set off becaause the new tile will stick up above the rest of the floor. Should I sharpen the chisel again?