Cracked Shower Grout
and what it means.

Start with the thing most homeowners have never been told: grout is not waterproof. It never was. Grout fills the space between tiles and takes the wear, and water passes through it the way water passes through concrete. The layer that keeps your shower dry sits behind the tile, and you have never seen it.

That one fact explains most of what follows. When grout cracks, the grout is not the problem. The grout is the thing that moved.

The location of the crack tells you what happened

Along an inside corner

Cracks where two walls meet, or where a wall meets the pan, mean somebody put grout in that corner. Corners move. Two planes of a house expand and contract against each other all year, and rigid grout in that joint has one way to respond. Those joints should carry color-matched silicone instead, which flexes. We use silicone on every change of plane for this reason, and a corner crack in someone else’s shower is the first thing we spot.

Across a field of tile

Cracks out in the middle of a wall or floor point at the substrate. Tile is only as flat and as still as the surface under it. A floor that flexes underfoot, a wall of plain drywall behind a shower, or thinset spread too thin will crack a grout line in a straight run.

Crumbling and grey where it stays wet

Low on the wall and around the drain, grout that has gone soft has been sitting in water long enough to break down. That one is telling you water is not leaving.

The test that tells you how bad it is

Press the tile around the crack. If a tile sounds hollow when you tap it, or moves at all, the bond behind it has failed and no amount of surface work will fix that. Water has been getting behind the tile, and the substrate underneath has taken the same water.

If the tile is solid and the crack runs no further than one corner or a short line, you are in repair territory. We cut the old grout out of the affected lines, clean the joint, and replace it, with silicone in the corners this time.

About sealing

Sealer is worth doing on natural stone and on porous grout in a shower, and it will keep stains out. It does not make a shower waterproof, and it does not stop cracks. Anyone selling grout sealing as a fix for a leak is selling you a delay.

Tearing it back to the studs

Sometimes a shower is past patching, and we would rather say so at the quote than take your money twice. Water behind the tile for a year or more means wet substrate more often than not, and wet substrate means the rebuild is the honest answer. We open a small area to check before we quote whenever we can, so the number you sign reflects what is back there.

That is the same reason we build our own showers the way we do. The pan, the curb, and the first four feet of wall get waterproofed and flood-tested before a single tile is cut. More on how we set tile is on the tile installation page.