Shower Leaking Through Grout? What to Do (and When to Call a Pro)

Water coming through your shower grout is urgent — but it doesn't always mean a full rebuild. Here's how to tell how bad it is, what you can check tonight, and when it's time to call a tile pro.

First, the technical truth most homeowners never hear: grout is not waterproof. Cement-based grout absorbs water — that's normal and by design. The layer that actually keeps water out of your walls and subfloor is the waterproofing membrane behind the tile (a painted-on membrane, sheet membrane, or a traditional pan liner, depending on how the shower was built).

That distinction is everything. Water visibly passing through grout can mean two very different things: surface-level wear you can fix in an afternoon, or a failed waterproofing layer that no surface repair will stop. This guide walks you through telling them apart.

Tonight's triage: four things to check

Before you touch anything, do a 10-minute inspection. You need to know whether the problem is at the surface or behind it.

1. Caulked corners and change-of-plane joints. Look at every inside corner — where walls meet, where the wall meets the floor or tub, around the curb. Grout in corners cracks because the two planes move independently; those joints should be caulk, not grout. Cracked, missing, or moldy caulk here is the single most common source of "leaking grout."
2. Loose or hollow tiles. Tap the wall tiles lightly with your knuckle, especially low on the walls and around the drain. A solid tile sounds dull and firm; a hollow or drummy sound means the bond behind it has failed. One loose tile is a repair. Several is a pattern.
3. The ceiling or wall below. If there's a room under the bathroom, check its ceiling for water spots, bubbling paint, or discoloration. Staining below means water is getting past the membrane — that's the line between a surface fix and a rebuild.
4. Smell. A persistent musty or earthy smell in the bathroom that cleaning doesn't fix usually means moisture trapped behind the tile. Trust your nose.

What you can safely try yourself

If the triage points to the surface — intact membrane, no stains below, tiles solid — two DIY fixes cover most cases:

Re-caulk the change-of-plane joints. Cut out the old, cracked caulk in the corners, clean the joint thoroughly, let it dry, and run a fresh bead of 100% silicone caulk (not latex). This is the fix for the majority of "my grout is leaking" calls I see. It costs a few dollars and an hour.

Clean and seal the grout. Scrub the grout lines, let them dry completely, and apply a penetrating grout sealer. Be honest with yourself about what this does: sealer resists staining and slows surface absorption. It does not waterproof a shower and it will not stop a real leak. If water is still passing through after re-caulking, sealer won't save it.

Signs you need a pro now

Stop with the surface fixes and call a tile professional if you see any of these:

• Water spots, bubbling paint, or soft drywall on the ceiling or wall below the shower.
• Visible mold that returns after cleaning, or a musty smell that won't go away.
• Multiple loose or hollow-sounding tiles, especially near the floor or curb.
• The leak continues after you've properly re-caulked the corners.

Each of these suggests the waterproofing layer itself has failed — and no amount of grout, sealer, or caulk fixes a failed pan. Continuing to patch the surface just gives the water more time to rot the framing.

How a pro actually diagnoses it

A proper diagnosis doesn't start with ripping out tile. It starts with a flood test: the drain is plugged, the shower pan is filled with a couple of inches of water, and the water level is marked and watched — usually for 24 hours. If the level drops, the pan leaks. If it holds, the membrane is sound and the problem is at the surface.

This is also how competent installers verify their own work: a flood test is standard practice before tile goes on a new shower pan, precisely because it's the only way to prove the waterproofing holds. If a contractor proposes rebuilding your shower and doesn't mention testing the new pan, that's a red flag.

What it costs to fix — honestly

Re-caulking corners is a cheap afternoon. A shower rebuild is not — it's demolition, a new pan and membrane, tile, and grout, which is why you want a correct diagnosis before anyone swings a hammer. If you're weighing a full replacement, our breakdown of bathroom remodel costs in the Twin Cities covers what the line items actually run.

One warning from the trade: don't let a handyman "fix" a failed pan by tiling over it or smearing on surface coatings. Covering a failed waterproofing layer hides the leak while the damage continues underneath. A failed pan gets rebuilt — there is no shortcut version.

And if you're already thinking bigger — say, ditching the tub entirely — our guides on walk-in shower vs. tub and tub-to-shower conversion costs in Minnesota will help you decide whether a conversion makes sense while the shower is apart.

If your triage found any of the red flags above, don't wait on it — water damage gets more expensive every week. Send us a few details and photos and we'll tell you straight whether it's a repair or a rebuild, with a free estimate either way.