Okay, so my shower is leaking. Narrowed it down to the cartridge valve. I have replaced all the fixtures in the other bathroom, so I have some familiarity. However I take off the backer plate and find this FNG situation.   NOTHING is ever easy for me.





So given what I am looking at, and the fact that I cannot access 2 screws, or the brass ring I am going to have to cut some of the fiberglass shell. Got 2 screws out, and it is hard to see in the picture but there is like black rubbery foam at the top and inside the hole, it blocked part of the top screw but seemed realtively easy to move.

How they hell can I do this and not F-up the process? I am not used to cutting fiberglass. I know to do it the first time, masking tape, pilot hole, hole saw, but the builder dicked that up. Should I use masking tape and a hack saw, or? I can clearly see what the backer plate would cover, and where I would be okay, but I am worried about cutting and vital pieces I cannot see.

Any help would be greatly appreciated.

whats on the back side?

easier to patch sheetrock then the fiberglass.

Do you own a dremel tool or roto-zip?

If so, that's what I would use.  Chuck up a cutting bit and control depth of cut on your own or use the router-like depth guide that can be purchased at a hardware store (I know Dremel has one).

Medicine cabinet on the other side, took that down and can see, but can't get to the screws. It should make cutting easier though. As I can see where I could cut.

Edit to add, you guys rock, thanks for the help and processing. Here is what it looks like now. All I have to do now is wait for the load of laundry to be done so I can shutoff the main and pull the valve.