Is my plan to replace a bathtub faucet reasonable?

Question

I recently bought a house. It has an upstairs and downstairs unit. The previous owners refinished the bathroom prior to the sale with crappy PVC siding for the bath walls. According to YouTube videos, the ultimate authority on these things, this is not a totally invalid way of paneling a shower, if done right, which they didn't.

The hole for the shower head nipple had an enormous, ragged hole cut for it that exposed the plaster - it's clearly impossible to use the shower in that state without rotting the walls instantly. Thinking they just couldn't be bothered to measure their holes correctly (they couldn't, but that's beside the point), I poke around and realize the issue.

1. The nipple has a metal collar around it.
2. Since the nipple seems to have been a straight length of pipe that was bent downwards, the collar will not slide forward because of the deformed cross section - so I can't just pop off the shower head attachment, pull the collar and replace.
3. Behind the collar, the pipe is straight, and so the collar could be slid backwards and removed that way, if I could remove the section of the pipe.
4. The joint of that pipe is well within the plaster, meaning a pretty significant demo/rebuilding project to get at the joint, which is probably brazed. I have concerns about getting it detached assuming I was even able to get at the joint and apply torque enough somehow to pull it loose.

My current plan is to:

1. Take a Dremel, and cut/grind the narrowest part of the metal collar off, allowing me to slide it down and forward, and remove it that way. Discard it.
2. Install the plastic panel, as shown in the photo, with a small hole. Place a 1/2" split plastic escutcheon flange on the faucet, sealing the split, its contact with the faucet and it's contact with the wall with silicone caulk - a water proof seal.

My hope is that someone with more experience knows of a simpler/better fix before I do something irreversible like cut the metal collar.

Also I know the real solution is, gut reno and redo the bathroom. That's on the list, but between roof, paint, floors (cat piss stains/stink everywhere), windows and weatherization, I need to get a little money coming in before I can hit any larger projects. The minimum solution has to be something that is water tight for at least a year's use before I can shell out the dough for a pro to do things correctly, top to bottom.

Answer 1

The shower arm is, in point of fact, nearly always a threaded (pipe threads) joint, as that's how standard chromed shower arms come. If the other plumbing is soldered, it's usually (should be, for sure) a "drop ear elbow" so that it's properly secured to the framing - assuming it was put in by competent workers, of course. With plaster and wooden lath, it's probably galvanized pipe, unless it was replaced more recently.

Consider that if it were brazed, the escutcheon would have the same problem sliding on from the end of the pipe as you have sliding it off the end of the pipe.

An inexpensive borescope camera (that works with computer/phone, in the modern era) may be worth its price for examining the actual situation with minimal destruction. Though with exposed lath next to the hole, a strong flashlight and an eyeball may be all that's needed to see it.

Honestly, given the state of the wall there and that it will end up hidden behind plastic when finished, chopping an access hole would add almost nothing to the patch you'll need to make before putting the new plastic over the plaster already in need of a large patch.