Tub drain leaking

I discovered our fiberglass tub was leaking and thought it just needed new putty under the drain (between drain and inside of tub). Didn't work though. I ended up getting a new tub drain shoe, drain and rubber gasket. Installed that with new putty. Still leaks. It is really rough on the underside of the tub. Can I expect this to ever seal? See pic below.

Sealing doesn't happen from the underside, and you shouldn't be using putty underneath the tub.

I didn't use putty underneath the tub. I used it where you are supposed to on the other side. I just posted this pic to show where it is leaking. The discoloration is from what is probably years of leakage. I have tried it about 5 times and it still won't stop leaking. When I unscrew the drain there is a nice, even bead of putty around the lip of the drain every time. Thus, why I am thinking the irregular surface and gasket on the underside are at fault. Maybe I am not tightening it enough. I don't want to really crank down on it and risk cracking the fiberglass, though. Thanks for your reply.

The ONLY sealing is on the underside of the tub, with the rubber gasket. Putty on top just keeps the water in the tub when the plug is closed, (and if you have a "trip lever waste" it would not be needed at all). IF the underside is NOT smooth, and sometimes not "level", it WILL leak.

When I run my finger around the underside (rough, unfinished side) of the drain hole, before installing the shoe, it is very irregular and rough (which you can pretty much tell from the photo above, I think). I have only installed a few steel tubs prior to this and never had any issues. I just thought there must be tons of these fiberglass tubs out there, and that maybe there was some special trick that I wasn't aware of (e.g. put a bead of silicone caulk on the underside gasket first?). There are a few fine cracks in the tub finish well away from the drain. I obviously don't want to put in a whole new tub if I don't have to, but it seems this tub might be circling the drain....It is about 26 years old. Thanks for the reply.

If the fiberglass strands have been debonded and or broken, you'll proably never get it to seal. If you could sand it flat and smooth back to solid material, you have a chance, but the thing is often thin to start out with.

Basement_Lurker said:

Sealing doesn't happen from the underside, and you shouldn't be using putty underneath the tub.

Click to expand...

Ugh, what I meant to say was that "waterproofing" of the tub happens from the top, not the bottom. But unless you crank down the basket enough, the shoe will never seal to the underside of the tub properly; the rubber gasket will compress a little allowing you to get the joint fairly tight without destroying the tub. As always, Hj's answers are %100 correct and concise. If you are finding that you have rough patches of fiberglass around drain hole, you can carefully scrape them flat with a flat bade screwdriver or take the safer route and sand them.

I cranked it down pretty tight previously, but will give the sanding a go... Thanks to all.