Fiber glass tub

Installed whirlpool tub that was fiberglass re-enforced. Poured mortar to support weight of tub, but the tube leaks around the drain. I used plumber putty and the drain has a small rubber gasket... Help

leak

The drain is not tight or maybe not level, the tub is defective, the drain is defective, or the gasket is the wrong one. Start with these four possibilities and work up to the real problem. It should not leak. The plumber's putty is to keep the water in the tub, not prevent a leak underneath.