How often should you seal tile grout?

Short answer

Seal the tile grout every 1 to 3 years. Grout in a shower gets the yearly end of that range, because it's wet every day. Grout on a kitchen floor or a backsplash can go the full 3 years. If the grout is epoxy, skip this job entirely, since epoxy grout is waterproof without a sealer. The job takes 60 to 120 minutes for a bathroom and the sealer costs $15 to $40.

Why it matters

Ordinary grout is cement, and cement is porous. Water soaks into it the way it soaks into a sidewalk. In a shower, that means the grout stays damp between showers, which is where the black mildew lines come from. In a kitchen, it means spilled coffee and grease soak in and stain, and the stain can't be scrubbed out because it's below the surface.

Over years, water that's been soaking into grout lines gets behind the tile. Grout crumbles out of the joints, tiles loosen, and in a shower the wall behind them takes on water. A penetrating sealer soaks into the grout and blocks the pores, so water beads on top instead. It wears off with cleaning and traffic, which is why the job repeats, but while it's there it keeps the grout clean and the tile stuck down.

When to do it more often

A shower: every year. Daily water and soap scum strip a sealer faster than anything else in the house.
Epoxy grout: skip it. Epoxy isn't porous and doesn't take a sealer.
A floor that gets mopped often, especially with a strong cleaner: the sealer wears faster, so test it each year and reseal when water stops beading.
Freshly installed grout: seal it as soon as the installer's cure time is up, before it takes its first stain.

What you need

A small brush or an applicator bottle with a sponge tip, to put sealer on the grout lines and not the tile
Clean rags, to wipe sealer off the tile face before it dries there
A penetrating grout sealer, the kind that soaks in rather than forming a film

Steps at a glance

Clean the grout thoroughly and let it dry completely, which takes a day or more in a shower.
Test a drop of water on the grout: if it beads, the old sealer is still working and you can wait.
Work sealer along the grout lines with the brush or applicator, a small area at a time.
Wait as the label says, then wipe any sealer off the tile surface before it hazes.
Apply a second coat if the first soaked in fast.
Keep the area dry for the cure time on the label.

You're done when a drop of water beads on the grout instead of soaking in and darkening it.

Signs it's overdue

Water soaks in and darkens the grout instead of beading on it.
Stains that won't clean off, in the grout rather than on the tile.
Grout crumbling out of a joint.
Mildew along the grout lines in the shower that comes back right after cleaning.

DIY or pro

This is an easy job, if a slow one. The brush work is tedious on a big floor, and the sealer has to go on dry, clean grout to soak in, so most of the time goes to cleaning and waiting. Open a window. Penetrating sealers are solvent-based and smell strongly until they cure.

A cleaning company charges $200 to $500 to deep clean and seal a bathroom's grout, often with a machine that gets grout cleaner than hand scrubbing can. That's good value for a bathroom whose grout is stained through, since sealer locks in whatever stain is already there, and worth it for a large tiled floor. For a shower or a backsplash, an afternoon and a bottle of sealer do the same job.

Safety

Chemicals: penetrating sealers give off strong fumes. Open windows, run the exhaust fan, and wear gloves. Keep the sealer off your skin and don't use it near a pilot light or an open flame until the fumes have cleared.

FAQ

How do I know if grout needs to be sealed?

Put a drop of water on it. If the drop beads up, the sealer is still working. If it soaks in and the grout darkens, it's time to reseal.

Does new grout need to be sealed?

Yes, once it has cured. Unsealed grout starts absorbing stains from its first day.

Can you seal grout without cleaning it first?

No. Sealer locks in whatever is on the grout, dirt and stains included. Clean it, let it dry fully, then seal.

What kind of grout sealer is best?

A penetrating sealer, which soaks into the grout and blocks its pores. Film-forming sealers sit on top, look glossy, and peel or wear through in traffic.