Grout

What is grout?

Grout is the material that fills the gaps between tiles after they are set. It stiffens to support tile edges, blocks dirt and moisture from getting under the tile, and creates a clean, finished look. Most DIYers encounter grout during tile installations in bathrooms, kitchens, and entryways, but it also appears in stonework and some masonry repairs.

Where is grout used?

Grout is used anywhere tiles meet: floors, walls, showers, tub surrounds, kitchen backsplashes, hearths, countertops, and even outdoor patios if the product is rated for exterior use. Properly selected and installed, grout helps distribute minor loads, reduces chipping at tile edges, and makes cleaning easier.

Types of grout

Understanding the main types helps you match the product to the job.

• Cementitious grout: The most common for home projects. It is mixed with water and cures by hydration.

  • Sanded: Contains sand to limit shrinkage. Best for wider joints (about 1/8 inch to 1/2 inch). Good for floors and most porcelain or ceramic tiles.
  • Unsanded: Smooth, no sand. Best for narrow joints (about 1/16 to under 1/8 inch) and for softer, scratch-prone tiles like polished marble or glass mosaics.
  • Polymer-modified: Cement grout with additives that improve strength, flexibility, and stain resistance. Commonly labeled as improved performance or high-performance cement grout.

• Epoxy grout: A two- or three-part system made from resins and hardeners. Highly stain resistant, very strong, and low porosity. Great for showers, steam rooms, countertops, and high-traffic floors. Has a shorter working time and a more involved cleanup.

• Single-component or pre-mixed (often urethane or acrylic): Ready to use out of the pail, no mixing required. Good stain resistance and flexible; popular for backsplashes and small jobs. More expensive per unit and not all products are rated for full submersion or exterior use.

• Furan grout: Industrial-grade, chemical resistant. Rarely used in homes.

How to choose the right grout

Match the product to joint width, tile type, location, and maintenance expectations.

• Joint width and tile material

  • Under 1/8 inch joints: choose unsanded cement or an epoxy with fine fillers.
  • 1/8 inch and wider: choose sanded cement or epoxy. For natural stone that scratches easily, stick with unsanded or a stone-safe epoxy and test first.

• Location and exposure

  • Dry walls and backsplashes: sanded or unsanded cement works well; pre-mixed is convenient.
  • Floors and high traffic: sanded cement, modified cement, or epoxy.
  • Wet areas (showers, tub surrounds, steam): epoxy or polymer-modified cement with a quality sealer. Verify the product is rated for continuous moisture if used in a shower pan or steam shower.
  • Exterior or freeze-thaw: use products specifically rated for exterior use and follow temperature and curing guidelines.

• Color and appearance

  • Light grout brightens a space but shows stains sooner.
  • Mid-tone grays hide dirt and often match popular porcelain tile bodies.
  • Dark grout can frame tiles and hide grime but may show efflorescence or haze if not cleaned correctly.
  • Request color swatches and test on a spare board; grout can dry lighter than it looks wet.

• Maintenance preferences

  • Cement grouts typically benefit from a penetrating sealer after curing; plan on periodic resealing.
  • Epoxy and many single-component grouts are more stain resistant and usually do not need sealing.

How to apply grout successfully

The exact steps vary by product, but this workflow covers most cement grouts; always read the manufacturer’s instructions.

1. Prep joints: Joints should be clean, consistent depth, and free of thinset ridges. Vacuum dust and wipe with a damp sponge.
2. Mix: Combine powder and clean water to a creamy, peanut butter-like consistency. For cement grout, allow a short rest (called slaking), then remix. Avoid adding extra water after slaking.
3. Apply: Use a rubber grout float at about a 45-degree angle to pack grout into the joints. Work diagonally across tiles to avoid pulling grout back out.
4. Strike and shape: Hold the float nearly vertical to remove excess, again moving diagonally.
5. Initial wash: After the surface dulls slightly (often 10–20 minutes), wipe with a barely damp sponge in light, diagonal passes. Rinse the sponge frequently and wring thoroughly to avoid overwetting.
6. Final buff: After a light film appears, buff with a microfiber towel. For epoxy, use the manufacturer’s emulsifier and cleanup pads.
7. Cure and seal: Let cement grout cure as directed (often 24–72 hours). Apply a penetrating sealer if required. Keep the area dry until curing is complete.

Tip: Maintain consistent water temperature and mixing ratios between batches to avoid color variation.

Maintenance and repair

• Routine cleaning: Use a pH-neutral tile cleaner and a soft brush. Avoid harsh acids or strong bleach; overuse can degrade cement grout and etch stone.
• Stain protection: Reapply penetrating sealer to cement grout periodically, often every 1–3 years depending on traffic and cleaners used.
• Haze removal: If a powdery film remains, use a grout haze remover compatible with your tile and grout type after initial cure.
• Regrouting: For cracked or stained joints, remove the top 1/8 to 3/16 inch with a grout removal tool or oscillating multi-tool, then regrout. For persistent discoloration, grout colorants can recolor and seal in one step.

Common mistakes to avoid

• Adding too much water during mixing or cleanup, which weakens cement grout and causes color washout.
• Using sanded grout on scratch-sensitive tile like polished marble or some glass; always test.
• Choosing unsanded grout for wide joints, leading to shrinkage and cracking.
• Cleaning too soon or too aggressively, pulling grout from the joints.
• Skipping slake time for cement grout, which affects consistency and strength.
• Failing to seal cement grout where needed, especially in kitchens and baths.
• Not following temperature and humidity limits; extremes can affect cure and color.

Related terms

• Thinset mortar: The adhesive that bonds tiles to the substrate, applied before grouting.
• Caulk: Flexible sealant for movement joints and changes of plane (tile to tub, wall corners). Use color-matched caulk, not grout, at these locations.
• Grout float: Rubber tool used to press grout into joints.
• Grout sealer: Penetrating liquid that reduces water and stain absorption in cement grout.
• Efflorescence: White mineral deposits that can form on cement grout; often managed with gentle cleaners and proper curing.

Practical examples

• Kitchen backsplash with glass mosaic: Joints are narrow; choose unsanded cement or a glass-approved epoxy. Mix small batches, wipe gently to avoid scratching, and consider a light gray to hide minor stains.
• Porcelain tile bathroom floor, 3/16 inch joints: Use sanded or polymer-modified cement grout. After curing, seal to resist spills. A medium gray helps mask dirt between cleanings.
• Shower walls: Epoxy grout provides top-tier stain and moisture resistance. If using cement grout, pick a high-performance modified version and seal after cure. Use color-matched silicone caulk at corners and where tile meets the tub or pan.
• Outdoor porcelain patio: Select grout rated for exterior and freeze-thaw conditions. Follow temperature guidelines and protect from rain during curing.

With the right type, careful application, and routine care, grout supports your tile, keeps water out of places it should not go, and helps your project look sharp for years.