Newly installed shower drain, hole too large?

[jimmyfo]

Hi, we have a company doing the plumbing for a new bathroom going in. They were going to do the shower drain fittings and the membrane on the same visit, but I asked them to come put the drain on first so I could add some preslope, then they'd come out to do the membrane after that. They agreed for a price, so we went ahead and did that. My expectation was that the hole they needed would be about 4" wide and the drain piece would be a little above the subfloor for the slope.

However, as per the pics attached, they drilled a 7" hole (angled edges) and set it flush. My main concerns are:

- Is this stable? It's new 3/4" ply on 16" on center, with blocking at transitions. However a 7" hole seems huge and there is some play (not much) in the fitting.
- How can I slope at this point? I can feather it out to the edge of the drain, but it seems kind of pointless, won't the mortar break up in the future with how thin it is?

Should I cut out a 16" square section and replace with a new fitted piece myself? Is it not worth it? I tried added some cleating from underneath, but it's not that great.

Thoughts? I've been really happy with them so far, but I'm concerned about potential longevity issues.

 

[Jadnashua]

Deck mud is strong in compression, but lousy at bending strength. Without support under the drain it can move and fail. Ideally, a patch would span two joist bays so that it isn't hanging on the edges but if you can add good blocking, then yes just cutting one bays width can work. Industry standard call for a minimum deck mud thickness to be like 1.25" in each layer, but people seem to get by with around .75" under the drain. It looks like it's a bit low to me. If it was over a slab it could taper down to much thinner as a slab would not flex and you can bond it to it. The wooden subfloor ends up floating so it needs lath and thickness to survive.

Www.johnbridge.com has a good description in their liberry (sic). I'd read that for guidance. The TCNA handbook has specs on how to build most anything tiled and is the industry's bible. The biggest problems with a conventional tiled shower are preslope, curb dam corners, how to handle anchoring the bottom of the cbu ,and the curb itself, but there are lots of ways to mess up. It's not difficult but is very detail oriented. Get one item wrong and the whole thing is impacted.

 

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[jimmyfo]

Thanks for the reply, I'll check them out.

My main concern (I opened up the ceiling below) was it was so thin by the edge of the 7" hole that the holding screws were basically splitting the plywood. I added 2x4 cleating to try to connect, but I'm just not comfortable with it and think I may go the rout of cutting off the 2" pipe and a 16x16 square of the floor and adding new blocking and plywood. It's frustrating since I JUST laid all the plywood and now it's time to cut it up and out again.