Shower Pan Leak Repair: Signs, Causes and When to Rebuild

Shower pan leak repair is the work of finding and fixing a failed waterproof layer under a tiled shower floor. You know the pan is leaking when water shows up below the shower, the floor grout stays dark for days, or the bathroom smells musty. A torn liner or clogged weep holes cannot be patched from the top. In most cases, a real fix means rebuilding the shower floor.

Key Takeaways

• The pan sits under the tile. It is a liner or membrane that catches water and sends it to the drain.
• Three main causes: a torn or punctured liner, clogged weep holes, and no slope under the liner.
• Grout is not the waterproofing. Regrouting can slow a leak, but it cannot fix a failed pan.
• Most failed pans need a rebuild. We replace them with a Schluter Kerdi foam tray or a new mud pan.
• Cost (as of 2026 pricing): replacing a leaking shower floor with a Kerdi tray and new curb runs $4,100 to $4,500 in Greater Boston, MA.

How Can You Tell the Shower Pan Is Leaking?

A leaking pan shows itself below and around the shower, not on the tile face. Look for these signs:

• A stain on the ceiling below that darkens after showers.
• Floor grout that stays dark long after the shower dries. That means water is trapped in the mortar under the tile.
• Water at the base of the curb or on the bathroom floor outside the shower.
• A musty smell or black spots in the floor grout that come back after cleaning.
• Loose or hollow floor tiles near the drain or the curb.

Some of these signs also come from failed grout or caulk. That is why we test before we quote a rebuild. A flood test plugs the drain and fills the shower floor with water. If the ceiling below gets wet, or the water level drops, the pan has failed. If the floor holds water but the leak comes back when the walls get wet, look at the walls or the curb instead. Our guide on a shower leaking through ceiling below walks through those checks.

Seeing a ceiling stain under your shower? Get a free estimate for your shower pan leak repair. Send photos of the shower floor, the curb and the stain below, and we reply the same day.

What Causes a Shower Pan to Leak?

Most pans fail for one of three reasons: the liner breaks, the weep holes clog, or the liner was laid flat. All three hide under the tile. You cannot see them until the damage shows up somewhere else.

What Is a Shower Pan Liner?

A shower pan liner is a sheet of PVC or similar plastic under the mortar bed of an older shower. Water soaks through the grout and the mortar, hits the liner, and runs to the drain. The liner clamps into a two-part drain. It also wraps up the walls and over the curb.

Torn or Punctured Liners

Liners fail at their weak points. Folded corners crack with age. Nails or staples on top of the curb punch holes right where water runs. A loose drain clamp lets water slip past the liner at the drain. Each of these sends water into the subfloor instead of down the pipe.

Clogged Weep Holes

The drain in a liner pan has small weep holes at the level of the liner. They let water that soaked through the mortar escape into the drain. If mortar or debris clogs them, water has nowhere to go. The mortar bed fills up like a sponge. The grout stays dark, mold grows, and the water finds the next weak spot in the liner.

No Slope Under the Liner

A good liner pan has a pre-slope, a layer of mortar under the liner that pitches to the drain. Many older pans skip it. The liner then lies flat on the subfloor, and water pools on it. Standing water on the liner keeps the mortar wet all the time. The finished floor itself should slope 1/4 inch per foot toward the drain, per common shower building practice.

Dark floor grout that never dries can look like a cleaning problem. Our guide to why is my grout turning black explains how to tell mold on the surface from water trapped below it.

Can a Shower Pan Be Repaired or Must It Be Rebuilt?

A true pan leak almost always needs a rebuild of the shower floor. The liner sits under the mortar bed and the tile. There is no way to patch it from the top. Anything sold as a seal-over fix only treats the surface.

A repair without tear-out does make sense in a few cases:

• The flood test passes. The pan holds water, so the leak is in the grout, the caulk or the curb. Full regrouting and fresh silicone may solve it.
• The leak is only at the curb. A cracked curb can sometimes be rebuilt without redoing the whole floor. See our guide on why is my shower leaking from the bottom.
• The pipe below is leaking. A drain pipe or trap leak under the floor is a plumber's repair, not a pan failure.

If the flood test fails, plan on a rebuild. We remove the floor tile, the mortar bed and the old liner. We usually take off the bottom row or two of wall tile as well. That lets the new waterproofing overlap the walls the right way. Then we check the subfloor for rot before building anything new.

Mud Pan vs Kerdi Tray: Which Is Better for a Rebuild?

Both work well when they are built right. We pick based on the shape of the shower, the drain location and the floor height. In both cases, we connect the Kerdi drain ourselves. A plumber is only needed if the drain or the valve has to move.

Schluter Kerdi Foam Tray

A Schluter Kerdi-Shower tray is a pre-sloped foam base. We set it in thinset and cover it with Kerdi membrane. The waterproofing sits right under the tile, so the mortar never gets soaked. Schluter calls for 2-inch overlaps at membrane seams. Where the tray or curb meets the wall, we seal the corner with Kerdi-Band. The walls above get RedGard liquid waterproofing.

Mud Pan

A mud pan is a sloped mortar bed floated by hand. It works for odd shapes, long showers and drains in unusual spots. We float it to the right slope, waterproof it, and tie it into the drain. It takes more skill and more drying time than a foam tray.

On the rebuilds we have done since 2016, we recommend the foam tray for most standard showers. It is lighter and faster, and it removes the wet mortar bed that causes so many old leaks. We go with a mud pan when the shower shape calls for it.

How Much Does Shower Pan Repair Cost?

A leaking shower pan repair cost depends on whether the pan has truly failed. Surface work is cheap. A rebuild is priced like new shower floor work. These ranges are based on current pricing in the Boston area.

These prices are labor plus setting materials, based on current Greater Boston rates. A full shower rebuild takes 4 to 8 days. A floor-only rebuild is shorter, but the mortar or thinset still needs time to cure. You buy the new floor tile, and we can recommend suppliers. We supply the tray, membrane, thinset and grout.

Is It Worth Fixing a Shower Pan Leak Right Away?

Yes. Every shower on a failed pan adds water to the subfloor. Wood rots, the ceiling below stains, and mold grows in the wall cavity. In winter, many Boston bathrooms stay closed up with little fresh air, so wet framing dries even slower. Waiting turns a floor rebuild into a framing and ceiling repair too.

Get Your Shower Pan Leak Fixed for Good

Good shower pan leak repair starts with a test, not a guess. If the pan holds water, the fix may be grout and caulk. If it fails, the floor comes up and a new tray or mud pan goes in. The Tile Council of North America guidelines cover the slope and membrane rules behind a good pan.

Aguirre Modern Tile has rebuilt shower floors across Greater Boston since 2016. We are a registered Massachusetts home improvement contractor (HIC #655072), fully insured with $1M liability coverage. In our experience, the sooner a pan gets fixed, the less framing has to come out with it.

Ready to stop the leak under your shower floor? Get a free estimate for your shower pan rebuild. Send a few photos of the floor and any stains below, and we reply the same day.

Back to shower leaking repair | Shower Tile Repair Complete Guide