Key Takeaways
Grout
Grout is a dense filler material used to fill the gaps between tiles after they have been set. It locks tiles in place, keeps moisture and debris out of the joints, and gives the finished surface a clean, finished look. Without it, tiles can shift, crack, or allow water to get underneath.
Grout is not an adhesive. It works alongside tile mortar or mastic, which bonds the tile to the substrate. The two materials serve separate functions and should never be substituted for each other.
The three types of grout and what they do
Walk into any home improvement store and you will find rows of grout products. Most of them fall into three categories, and picking the wrong one for your project is one of the easiest mistakes to make.
Sanded grout contains fine sand particles mixed into a cement base. That sand gives the grout body so it does not shrink or crack in wider joints. Use it when your tile gaps are 1/8 inch or wider. It is the standard choice for floor tile, most wall tile with wide joints, and outdoor projects.
Unsanded grout skips the sand, which makes it smoother and easier to press into narrow joints (under 1/8 inch). It also causes less surface scratching on polished stone or glass tile, where sand particles can leave marks. Because it has less bulk, unsanded grout tends to shrink slightly as it cures, so it should only go in the narrow gaps where it can bond tightly to both tile edges.
Epoxy grout is a different animal. It does not use cement at all. Instead, two components (a resin and a hardener) mix together just before use and cure into an extremely hard, non-porous surface. Epoxy grout resists staining, moisture, and most household chemicals. It works in showers, kitchen backsplashes, and commercial kitchens for that reason. The trade-off is price and working time: epoxy sets fast and costs considerably more than cement-based options. It is also harder to apply and clean up, so first-time tilers often find it unforgiving.
Match your grout to the tile surface
Polished marble, glass tile, and soft-glazed ceramics can scratch if you use sanded grout. Check with the tile manufacturer before choosing, because some surfaces require unsanded or epoxy grout regardless of joint width. A scratched tile surface cannot be fixed after grouting.
Why joint width determines your grout choice
The gap between your tiles is not just an aesthetic decision. It controls which grout you can physically use. A joint that is too wide for unsanded grout will crack as the material dries and shrinks. A joint that is too narrow for sanded grout will resist the material and leave voids, which lets water in.
Most standard ceramic and porcelain tiles are set with joints between 1/16 and 3/16 inch wide. Natural stone tiles, which are less uniform in size, often use wider joints to accommodate variation. Large-format tiles sometimes go as narrow as 1/16 inch, which requires a fine unsanded grout or a specific product designed for rectified tiles.
Tile spacers set during installation determine joint width, and you should have your grout type in mind before you ever place the first tile. Changing joint width after the fact means removing and resetting tile.
1/8 in.
Joint width threshold between sanded and unsanded grout
This is the widely recognized standard division used by tile industry guidelines: sanded grout for joints at or above 1/8 inch, unsanded for narrower joints.
48-72 hrs
Minimum cure time before sealing cement grout
Most cement-based grout manufacturers specify this window before applying penetrating sealer, though some formulations require longer.
1-2 years
Recommended grout sealer reapplication interval for wet areas
High-moisture areas like showers and kitchen backsplashes require more frequent resealing than dry, low-traffic surfaces.
Grout color and long-term maintenance
Color choice affects more than appearance. Light-colored grout in a high-traffic area or shower will show staining faster and require more frequent cleaning or resealing. Dark grout hides staining better but can fade unevenly over time, especially if harsh cleaners are used regularly.
Cement-based grout is porous by nature, which means liquids and oils work their way in over time. Sealing it with a penetrating grout sealer after the grout has fully cured (allow at least 48 to 72 hours) slows that process. Sealer is not permanent. In a shower or kitchen, plan to reseal every one to two years depending on use.
Epoxy grout sidesteps most of this because its surface is non-porous. If long-term stain resistance matters more than upfront cost and ease of application, epoxy is worth the extra investment for smaller, high-use areas like a shower floor or kitchen backsplash.
For more on why cutting corners during prep work leads to bigger problems later, see why DIY repairs go wrong.
What to do before you mix a single batch
Grout failure is almost always a preparation problem. Before mixing anything, confirm that the mortar holding your tile has fully cured. Pressing grout into joints while the mortar is still soft can shift tiles and weaken the bond.
Clean out the joints before grouting. Mortar squeeze-out, tile spacers, and dust will all interfere with adhesion. A grout saw, utility knife, or vacuum can clear the joints down to the tile edges.
Check your substrate for movement. Grout is rigid, and if the floor or wall underneath flexes, the grout will crack. A subfloor with give needs to be addressed before any tile or grout goes down. This is one of those situations where a licensed contractor's assessment is worth the cost of the inspection.
Mix grout to the right consistency. Too much water weakens cement-based grout and causes shrinkage cracks. Follow the manufacturer's ratio precisely, and let the mixed batch rest (slake) for the time specified before using it.
Finally, do not grout corners, the joint where a floor meets a wall, or any place where two surfaces change plane. Those spots need flexible caulk that can move with the building without cracking. Grout in those locations will fail, often within months.
Permits are rarely required for grouting alone
Replacing grout on an existing tile installation is generally a cosmetic repair that does not trigger permit requirements in most jurisdictions. However, if you are replacing tile and the work involves waterproofing a wet area, some local codes may apply. Check with your local building department if you are unsure.