I'm renovating a 1960 ranch-style house on slab. I removed the tub to repair termite damage to the alcove and since the tub had previously been refinished but was peeling. The tub is part of an overall plumbing upgrade. When getting estimates for the job I got different input on the tub. (Note: it's a long story why it's a DIY and not being done by professionals. The short versions are A: would not explain bid, B) did not even provide written bid, and C) too busy on other jobs to do mine).

The tub/shower has a cast iron P-trap under the slab. The trap was soldered to the drain via a short section of flared lead drain pipe. OD is just under 2" of the lead, ID is just under 1.5". The trap doesn't leak and drains clearly. One plumber wanted to jack hammer out the slab and original terrazzo floor and replace the functional CI with PVC all the way to the main stack. A second plumber made no comment and a third plumber suggested trimming off the flare and using a flex Fernco without the shield to connect to the lead and tailpiece. He specifically advised the non-shielded to compensate for the slightly irregular surface. There's a slight kink in the pipe about 3/4 down from the top, but the top is quite round and cut cleanly.

I went that route using a Fernco 1056-150/125. It fit snugly on both sections of pipe and I was confident that would work. During my rough-in inspection the inspector said it had to be a shielded coupling and wouldn't permit the flex coupling. I found a Mission Rubber T-150 that also appears to fit and is shielded.

Here are the questions:
1) How likely is the lead pipe to deform/crush if using the shielded coupling to the 60 in-lb limit?
2) Assuming it seals correctly, what's the best way to seal the area around the drain?

For #2, there was a soft/fragile cement/mortar mix around the drain when I removed it for the termite treatment. It wasn't complete and looked like it was added as part of some repair. I've filled the hole with sand to within about 1/2 - 3/4 inch of the bottom of the where the coupling ends. Should this be a thin layer of concrete? I asked the inspector and he said "in the old days they used to use tar" but that was about it. If cement, what sort of mix to make it more frangible for possible future repairs? Add extra water? Or is a 1/2 inch non-reinforced cement layer draped on sand about right?

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