A shower arm that moves more than 1/4-inch in and out of the shower wall usually indicates the shower riser needs securing. The shower riser is the pipe behind the wall that runs from the top of the shower diverter to the top of the shower. Usually the shower riser secures to the top sill at the ceiling, but occasionally the board that the bracket attaches to shrinks and swells, resulting in the mounting screws becoming loose. Securing the shower riser might involve cutting a hole in a wall to access the riser.
Find the access panel to your shower plumbing. The access panel is normally in the room opposite the shower fixtures. Open the access area to determine if you have room to work on the shower riser. You only need room enough to reach the center of the riser.
Cut the drywall at the center of two studs near the top of the shower riser with a utility knife if there is not enough room for you to work from the access panels. Cut out a piece of wall that is 1 foot tall. Remove the piece of drywall carefully to reuse it later.
Place the end of a tape measure on the inside of the stud to the left of the shower riser and measure to the inside of the stud to the right of the shower riser. Add 1/8 inch to the measurement and cut a piece of two-by-four board to the measurement with a circular saw.
Slide the board behind the shower riser and shower wall between the two studs. The edges of the board should be facing up and down with the face of the board facing you and the shower wall. Tap the board in between the studs with a hammer. You are wedging the board between the studs.
Pull the board against the shower riser. Place a riser clamp around the shower riser with each ear of the clamp against the face of the board. The riser clamps looks like a “C” with two tabs that straddle each side.
Secure the riser clamp to the board with wood screws and Phillips screwdriver. Place the cut piece of drywall over the hole you cut out and secure it with drywall screws and the screwdriver.