New Toilet Flange, Stone Slab Floor
Hi. I'm hoping somebody has encountered this situation and may have a suggestion.
The floor in our 2nd floor bath is a mashup. Most is 3/4" plywood, with some concrete sections around the borders. The toilet sits on a slab of some sort of stone -- slate or bluestone perhaps. It does flake. As you can see, the old flange has been removed from the drain pipe, which appears to be made of lead -- it's very soft. The pipe is not centered in the hole that has been cut in the stone, and it cannot be moved.
The stone slab is about 3/4" thick, and cut on an angle that increases the interior diameter from top to bottom. In other words, if the diameter of the hole on top of the slab is 5 inches, it flares out to a larger interior diameter at the bottom of the slab. It appears to be resting on the floor joists, so there is air underneath it.
A compression flange that fits around the exterior of the pipe does not appear to be an option. I could chip away enough of the slab so that it could fit around the pipe, but then it has nothing to sit on. My only option seems to be a pvc Sioux Chief flange with a metal reinforcement ring that fits the interior of the pipe and seals with a 3-ring rubber flange.
I would like to fasten the flange to the stone slab at three points, taking into account the fact that at least one of the fastening points will be close to the edge of the stone, so I need to cut clean holes in the slab, without destroying it. Then I would use toggle bolts to tighten down the flange. (By the way, the floor will be finished with 1/4" backer board and 1/8" ceramic tiles, all secured with modified thinset.)
Is there a tool that can give me a clean hole through the slab? If not, does anybody have an alternative solution? Thanks in advance.