What is behind the tile

Inside a typical shower wall are the valve body, a riser pipe running up to the shower arm, a pipe down to the tub spout, and the hot and cold supply lines feeding the valve. In older Fullerton houses those lines are usually copper or galvanized steel, joined with solder or threads, and every joint is a possible leak point.

Supply lines and the valve are under pressure all the time. The riser, arm and spout pipe only carry water while the shower runs. That difference is the key to finding the source without opening the wall first.

Signs of water behind the wall

  • Paint bubbling or peeling on the wall on the other side of the shower
  • Swollen or stained baseboard in the next room or closet
  • Tile near the valve or arm that has loosened or sounds hollow
  • Damp carpet or flooring along the shower's back wall
  • A musty smell in the room behind the shower
  • The water meter moving with every fixture off

What the timing points to

  • IfDamp appears with the shower off and the meter movesThenA supply line or the valve body under pressure; check with the valve stops closed.
  • IfDamp appears only while the shower runsThenThe riser pipe, shower arm joint or head connection.
  • IfDamp appears only when the tub fillsThenThe spout pipe or spout connection, or the overflow.
  • IfDamp appears after showers but not with the head aimed at the drainThenWater getting through grout, caulk or around the trim.

Tracing without tearing out tile

  1. Use any access panel.If a closet or room behind has a panel, open it and watch the valve and pipes while each fixture runs.
  2. Isolate pressure from flow.Close the valve stops if the valve has them. If the meter stops moving, the leak is at or after the valve.
  3. Aim the head at the drain.Running water with no spray on the walls separates pipe leaks from surface water getting in.
  4. Check the shower arm.Rock the arm gently with the water running. A drip at the wall flange suggests a failed arm joint.
  5. Plan the smallest opening.Once the source is known, open from the back side if possible, and only where the leak is.

What to ask

  1. Is the leak under constant pressure or only when the shower runs?
  2. Can you reach it from the back side of the wall?
  3. How big an opening do you expect, and who closes it?
  4. Will you check the condition of the other joints while the wall is open?

Common questions

Is a constant leak behind the wall urgent?

Yes. A pressurized leak runs around the clock. Shut the water at the valve stops or the main until it is repaired.

Can a shower arm leak be fixed without opening the wall?

Sometimes, if the leak is at the threads where the arm meets the fitting and the fitting is solid. A cracked fitting usually needs access.

Why are both sides of the wall damp?

Water spreads along framing and backer board. The damp area is usually larger than the leak itself.

General information for Fullerton, not a quote or professional advice. In an emergency, call 911.