I noticed a thin crack in my shower grout and thought “I will get to that next weekend.” Three months later, the tile was loose and there was a soft spot in the drywall behind it. A five-dollar, thirty-minute repair turned into a two-hundred-dollar weekend project.

Cracked grout is not cosmetic. Water gets behind it, rots the backer board, and eventually leaks into the wall cavity or the floor below. The good news is that fixing a small section of cracked grout is genuinely easy. Here is the right way.

Remove the Old Grout

Buy a grout removal tool — it costs six dollars and looks like a screwdriver with a carbide tip. Drag it along the cracked grout line to scrape out the old material. Go down about an eighth of an inch — you do not need to remove the entire depth, just enough for new grout to bond. Vacuum the dust out of the gap. Wipe with a damp sponge and let it dry completely.

If the grout is in good shape except for one crack, you only need to remove the cracked section. If the surrounding grout is also crumbling, widen your repair area.

Pick the Right Grout

Sanded grout for gaps wider than an eighth of an inch. Unsanded grout for narrower gaps. Using sanded grout on a thin line will leave pinholes. Using unsanded on a wide gap will crack as it cures because it shrinks. The bag or box tells you the gap range — read it.

For shower floors and areas that see standing water, consider epoxy grout. It is more expensive and harder to work with, but it is waterproof and will never crack again. Worth the hassle for shower pans.

Mix and Apply

Mix grout to a peanut butter consistency — thick enough to hold its shape on a trowel but wet enough to spread. Press it firmly into the gap with a rubber grout float held at a 45-degree angle. Pack it in — voids and air pockets will crack later. Scrape off excess with the float edge.

Let it set for about 15 to 20 minutes — until it is firm but not fully hard — then wipe with a damp sponge in circular motions to smooth the line and clean the tile faces. Rinse the sponge frequently. A haze will form on the tiles; wipe it off with a dry cloth after the grout has cured for a few hours.

Seal It

Grout is porous. Unsealed grout absorbs water and eventually fails. Wait 24 to 48 hours for the grout to fully cure, then apply a grout sealer with a small brush or applicator bottle. Two thin coats are better than one thick one. Reseal every year or two.