I had to replace my shower arm. There is no clearance around the shower arm to make sure it is not leaking into the wall. I tried chiseling out some of the cement but it feels harder than thinset. Usually I can chisel out thinset or cement board easily. In this case I was not able to chisel it out successfully. I'm not sure what material they used but its hard like a rock. I went to the other side of the wall and cut out a piece of drywall. There is a piece of wood behind the brass fitting that the shower arm is connected to. I can see the copper pipe underneath it (see pictures). The pipe looks dry. The insulation feels dry. Is there anything else I should do to make sure its not leaking? Thanks all.

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