Why Is My Shower Leaking From the Bottom? 4 Causes and Fixes

A shower leaking from the bottom is water that escapes at the base of the shower, where the curb, the door and the floor meet the bathroom. The usual answer to “why is my shower leaking from the bottom” is one of four spots. It is failed caulk at the door or curb, cracked curb grout, a cracked curb, or a failed shower pan. The first two are small fixes. The last two mean rebuilding that part.

Key Takeaways

• Four usual sources: door or curb caulk, curb grout, a cracked curb, and the shower pan.
• The curb is the most common culprit. It takes direct spray and sits on the outer edge of the pan.
• A curb top must slope into the shower. A flat curb holds water against the grout and caulk after every shower.
• Caulk is a quick fix, not a cure. If the curb is cracked or the pan has failed, new caulk only buys time.
• Costs (as of 2026 pricing): a regrout and recaulk runs $700 to $1,800. A new Kerdi tray floor with a new curb runs $4,100 to $4,500.

Why Is My Shower Leaking From the Bottom? The 4 Common Causes

Water at the base of the shower almost always comes from one of four places. Check them in this order. It runs from the cheapest fix to the most expensive.

1. Door or curb caulk. Silicone runs where the door track meets the curb and where the curb meets the wall. It shrinks, peels and grows mold over time. Water then runs along the curb and out onto the floor.
2. Curb grout. Cement grout on the top and inside face of the curb takes a beating from the spray. Once it cracks, water soaks into the curb itself.
3. A cracked curb. Many older curbs are stacked lumber covered in mortar. Wood swells when it gets wet. That movement splits the grout and tile on top.
4. A failed shower pan. The pan is the waterproof layer under the floor tile. When its liner tears or its drain seal fails, water spreads under the tile. It often comes out at the lowest edge, right under the curb.

Tile itself is rarely the leak. Porcelain absorbs less than 0.5% water per ASTM standards. The weak points are the joints and the layers behind the tile.

Seeing a puddle outside the shower after every use? Get a free estimate for your leaking shower curb or pan. Send photos of the curb, the door track and the floor outside the shower, and we reply the same day.

How Do You Tell Which One It Is?

• Water only when you spray the door or curb: start with the door caulk and the curb grout.
• Dark, stained or crumbling curb grout: the grout has failed, and water may already be inside the curb.
• A crack along the curb tile, or a hollow sound when you tap it: the curb itself is breaking down.
• Water that seeps out hours later, or a stain on the ceiling below: the pan or drain is the likely source.

One simple test helps. Run the hand shower low on the floor, away from the curb and door. If the leak still shows up, look at the pan or drain. If it only leaks when you spray the curb, the problem sits up top.

Why Is the Shower Curb Often the Culprit?

The shower curb is the most common source of a leak at the bottom of a shower. It gets hit by spray every day. It sits on the outer edge of the pan. It is also the hardest part of the shower to waterproof well.

Cracked Curbs

In older showers, the pan liner wraps up and over a curb made of stacked 2x4s. Some installers nailed through the liner on top of the curb to hold it down. Every shower then pushes water through those nail holes. The wood gets wet, swells, and cracks the tile and grout above it. Once the curb tile cracks, you are past a caulk fix.

No Slope on the Curb Top

The top of a curb should pitch slightly back into the shower. That way water runs in, not out. On a flat or back-pitched curb, water sits on the grout after every shower. It soaks the cement grout, finds the caulk joint at the door track, and runs out onto your floor. A small level shows the problem in seconds.

Wood Curb vs Foam Curb

• Stacked 2x4 curb with mortar: common in older Boston showers. It swells when wet. The liner often has nails or staples through the top.
• Schluter Kerdi-Shower curb: waterproof foam covered in Kerdi membrane and set in thinset. It does not rot or swell. It ties into the pan with Kerdi-Band at the wall corners.
• Solid mortar curb: strong but heavy. It cracks if the framing under it moves.

Quick Fix vs Real Fix: Which Does Your Shower Need?

A quick fix seals the surface. A real fix repairs whatever let the water in. Caulk and grout are quick fixes. A curb rebuild or a new pan is a real fix.

Quick Fix: Recaulk and Regrout the Curb

We cut out the old silicone at the door track, the curb ends and the wall corners. We rake out cracked curb grout and regrout with Laticrete Permacolor. Then we run fresh 100% silicone at every corner and change of plane. This works when the curb is solid and only the joints have failed. If the whole shower has tired grout, full regrouting makes more sense than patching. Our guides on regrouting shower joints and caulk vs grout in shower corners explain the details.

Real Fix: Rebuild the Curb or the Pan

If the curb is cracked, hollow or soft, we take it down to the framing. We build a new curb, waterproof it, and tie it into the pan. Where a Kerdi tray or curb meets the wall, we seal the corner with Kerdi-Band. The walls above get RedGard liquid waterproofing. If the pan has failed, the shower floor comes up too. Read our guide to shower pan leak repair for how that rebuild works.

• Quick fix: one visit, low cost, and it works only if the curb and pan are sound.
• Real fix: more days and more cost, but it removes the cause.
• Wrong fix: new caulk over a rotted curb. It looks fine for a few weeks while the wood keeps rotting.

In our experience, a curb that has leaked for a long time often has damage hidden inside. We open it up, check the wood, and show you photos before we rebuild.

How Much Does It Cost to Fix a Shower Leaking From the Bottom?

A bottom leak costs far less to fix early. Caulk and curb grout are small jobs. A curb or pan rebuild costs more because the tile has to come off. These ranges are based on current pricing in Greater Boston, MA.

Most repairs take 1 to 3 days, depending on scope. You buy any replacement tile, and we can point you to suppliers that stock a close match. We supply the setting materials, grout and waterproofing. On a pan rebuild, we connect the Kerdi drain ourselves. A plumber is only needed if the drain or valve has to move.

Can You Keep Using a Shower That Leaks at the Bottom?

You can use it for a short time if the leak is small and only at the door. Wipe the floor dry after each shower. If water seeps out hours later, or a ceiling stain shows up below, stop using the shower. Every shower then adds water to the subfloor. Winter makes it worse in many Boston homes. Temperature swings stress caulk joints, so small gaps open faster.

Check the Tile Council of North America guidelines if you want the standards behind curbs and pans. They call for sloped surfaces and a sealed membrane under the tile.

Stop the Leak Before It Reaches the Subfloor

If you are still asking why is my shower leaking from the bottom, start at the curb. Check the caulk, the grout and the slope on top. Then rule out the pan. We recommend fixing the cause, not just sealing the surface. Aguirre Modern Tile has fixed shower curbs and pans across Greater Boston since 2016. We are a registered Massachusetts home improvement contractor (HIC #655072), fully insured with $1M liability coverage.

Ready to stop the water at the base of your shower? Get a free estimate to fix your shower curb or pan. Send us a few photos and we will tell you which fix you need, the same day.

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