In short
Yes, in most cases. Cement based grout is porous, and a penetrating sealer slows how fast spills and soil soak in. Seal only after the grout is clean and completely dry, because sealer locks in whatever sits in the pores. It does not make grout waterproof or stainproof, and it needs renewing every year or two on busy floors. Epoxy grout usually needs none.
Worth remembering
- Sealer buys time. Spills stay on the surface longer, which gives you a chance to wipe them up before they stain.
- A penetrating sealer does not make grout waterproof or stainproof. Try a small patch first, since some products deepen the color.
- Seal only clean, fully dry grout. Sealer traps any dirt or moisture left in the pores.
- Drop a little water on the grout. If it beads, the sealer still works. If the grout darkens, reseal.
What a penetrating sealer does
A penetrating sealer soaks into the pores of cement grout and leaves a water repellent layer inside them. A spill then rests on the surface for a while instead of sinking in at once, and that pause is the benefit. You get time to wipe it up before it becomes a stain.
Most penetrating sealers leave the grout looking much as it did, though some deepen the tone a little, so it is wise to try a small patch first. Sealed grout is also easier to clean, since soil has less to hold on to.
What it does not do
Sealer does not make grout waterproof, and it does not stop all staining. Anything left to sit long enough still gets in. Coffee, wine, oil and colored cleaners all deserve a prompt wipe, sealed or not.
Sealer is also not a cleaner. Applied over dirt, it fixes the dirt in place and the grout can darken beneath it. Film forming sealers sit on top instead of inside, change the sheen and wear away under foot traffic, so most floor grout is treated with the penetrating kind.
Which grout is worth sealing
- Cement based grout in kitchens, entries and mudrooms: yes.
- Shower walls and floors: yes, along with caulk kept in good repair.
- Bathroom floors: yes.
- A guest bathroom used a few times a month: optional.
- Epoxy grout: usually no, since it is already nonporous. Check the maker's guidance.
- Natural stone tile: it has its own sealer made for stone, so ask the supplier.
Why the grout must be dry
Grout takes in water during cleaning, and a damp pore cannot take in sealer. Sealing too early traps moisture, which can leave cloudy or blotchy grout and encourages mildew in a shower. In a humid bathroom or a cool basement drying takes longer than most people expect, so pick a stretch of dry weather and keep a fan running. If the grout still feels cool to the touch, it is not ready.
Doing it properly
Clean the grout and let it dry completely. For new grout, wait out the curing time on the label first. Apply the sealer with a small brush or an applicator bottle, keeping it on the grout lines. Wipe any sealer off the tile within the time the label gives, or it can dry as a haze.
Then keep water, feet and rugs off the floor for as long as the product label asks. Some sealers need a second coat, and the label says so.
How often to reseal
The label gives the interval. For busy floors it is commonly every year or two, and for walls it is longer. Between times, use the water test. If the drops bead up, the sealer is still working. If the grout darkens and drinks the water within a minute or so, clean the grout again, let it dry and reseal.
Questions, answered
Can I seal grout that is already stained or dirty?
Clean it first. Sealer locks in whatever is sitting in the pores, so dirt and stains get trapped and darken over time. After cleaning, let the grout dry completely, which can take a day or more in a damp room, before applying any sealer.
Do I need to seal grout in a shower?
Yes, if it is cement based, and the caulk needs to stay in good shape too. Sealer slows moisture from soaking in, but it does not stop leaks, so cracked grout or failed caulk still needs repair.
How can I tell if my grout is already sealed?
Put a few drops of water on a clean, dry grout line. If the water beads and stays for several minutes, a sealer is working. If the grout darkens and absorbs the drops, it is unsealed or the sealer has worn away.