Why is my tile shower leaking?

A tile shower usually leaks for one of five reasons: water escaping past the door or curtain, failed caulk at a corner or around the trim, a loose shower head or arm, a leaking valve or pipe inside the wall, or a failed pan, membrane or drain connection under the floor. The tile and grout are not what keeps water in. Cement grout soaks up water, and membrane makers state that mortars and grouts for tile are not replacements for a waterproofing membrane.^[2] When a properly built shower leaks, something in that hidden layer, or one of the joints around it, has given way.

The good news is that you can usually narrow it down yourself with water, a bucket and some patience, before anyone opens a wall.

Start with when it leaks

The timing is the best clue you have.

• Only during or right after a shower. Look at splash-out, caulk, the shower head, the drain and the pan.
• Only when someone stands in one spot, or only with the door open. Usually splash-out or a specific failed joint.
• All the time, even overnight. Suspect the supply pipes or the valve. EPA's simple test: read your water meter, use no water anywhere for two hours, then read it again; if it has moved at all, you probably have a leak.^[1]

The easy causes first

Splash-out. A curtain that does not reach the curb, a gap at the door hinge side, a worn door sweep, or a hand shower aimed at the door can all put water on the bathroom floor, where it runs under the baseboard and shows up in the ceiling below. Watch a normal shower from outside before blaming the tile.

Caulk. The inside corners, the joint where the walls meet the floor, the top of the curb, the door frame and the gaps around the valve trim and tub spout should be caulked, not grouted, because those joints move. LATICRETE recommends flexible silicone caulk at corners and changes of plane.^[3] Cracked, peeling or moldy caulk is a common and cheap leak. Recaulk, and let the caulk cure before testing; LATICRETE's 100% silicone caulk, for example, fully cures in 24 hours.^[3] For the method, see how to recaulk a tub or shower, and for how long caulk should last, how often to recaulk a shower.

The shower head. A drip where the head meets the arm can run down the arm and into the wall. EPA suggests checking for a tight connection between the shower head and the pipe stem and using pipe tape.^[1]

The causes inside the wall

The valve. A shower that keeps dripping from the head or spout when the handle is off has a worn valve cartridge or seat. That is a nuisance, not usually a hidden leak. A valve body or pipe joint leaking behind the wall is different, and often shows as a stain on the other side of the wall or in the ceiling below whether or not anyone showers. EPA's advice for more complicated valve leaks in showers that drip when not in use is to contact an experienced handyperson or licensed plumber.^[1] For valve-specific causes, see should I hire a plumber to fix my shower valve.

The causes under the floor

The drain connection. Pour water straight into the drain with the shower off. If that alone drips below, the leak is at the drain body or the pipe under it, not the tile.

The pan or membrane. If the drain test is dry but wetting the tiled floor leaks, the pan or membrane is the likely cause. Shower drains made for a liner or membrane have a bonding flange or clamping ring, and HYDRO BAN's data sheet, for example, calls for one with weep holes.^[2] In a traditional mortar-bed shower, water that soaks through the grout runs down to the liner and out through the weep holes. If those holes are clogged with mortar, or the liner is torn or was never turned up the walls and curb, water sits in the floor and escapes at the edges. Grout that stays dark long after a shower, loose floor tiles and a musty smell can be signs of a wet mortar bed.

The walls. If the floor and drain tests are dry, spray one wall at a time. A leak that appears only when one wall gets wet points to a failed membrane, an unsealed niche or a cracked board seam on that wall.

Why it matters to move quickly

Water that gets behind tile soaks wood and drywall where you cannot see it. EPA notes that mold can hide inside walls around leaking or condensing pipes,^[4] and that, if wet materials are dried within 24 to 48 hours after a leak, in most cases mold will not grow.^[4] Stop using the shower until you have found the source, and dry anything you can reach.

Stop and call a pro if

• Water is coming through a ceiling, especially near a light fixture, or the ceiling is sagging. Turn off the shower and keep people clear.
• The water meter test says there is a supply leak, or the valve or pipes in the wall are leaking. Altering the drainage or water supply system needs a permit under Virginia's building code,^[5] and Virginia requires a master tradesman licence as a condition of licensing plumbing contractors,^[6] so this is work for a licensed plumber.
• The floor test leaks, tiles are loose, or the floor feels soft. The pan or membrane needs to be opened and rebuilt, and there may be rot under it.
• You find mold inside a wall or across a large area.

For leaks elsewhere in the house, see how to find a hidden water leak. When you are ready to have it repaired or rebuilt, read what to ask a tile installer first. You can browse shower tile installers, look up flooring and tile businesses around Blacksburg, or read the other flooring and tile answers. To get the leak looked at, describe it on Loclis.