Grout for Mosaic Tile: Type, Color and Technique for Small Tile

On mosaics, grout can cover 10 to 25 percent of the surface, so it matters as much as the tile. Use unsanded or fine high-performance grout for the usual 1/16 inch sheet joints, epoxy for shower floors and kitchens, and a color you are happy to see in quantity. Clear thinset from joints before grouting.

On mosaics, grout is part of the surface

With large tile, grout is a thin network around the tile. With mosaics, it is a substantial part of what people see, touch and clean. The share of a surface taken up by grout depends on the tile size and the joint, and it climbs quickly as tiles get smaller. The figures below are pure geometry for square tile, so they apply to any material.

A 1 inch mosaic with a 1/16 inch joint needs roughly four times the grout volume per square foot of a 12x12 tile with a joint twice as wide. Bag coverage charts written around field tile will badly underestimate a mosaic job. Use the grout calculator with the actual tile size and depth, and see the grout joint area analysis and grout coverage table for more sizes.

Penny rounds, hexagons and other shapes

Round and irregular mosaics carry even more grout than squares of similar size. Penny rounds leave a wide, roughly triangular pocket where three circles meet, and the joint varies from narrow at the touch points to several times wider in the pockets. Hexagons pack efficiently, but their joints run in three directions, which makes floating and washing slower. Picket, arabesque and fan shapes create joints that change direction constantly. All of these favor a grout that handles a range of widths without slumping in the wide spots or cracking in the narrow ones, which usually means a high-performance cement grout or epoxy rather than plain unsanded grout.

Choosing the grout type for mosaics

For glass mosaics specifically, the glass tile grout guide covers scratching and translucency. For stone mosaics, see grout for natural stone.

The epoxy question

Epoxy is ideal for mosaic shower floors: small tile on a sloped floor means many joints sitting in water, and epoxy does not absorb water or soap, does not need sealing, and holds color. The tradeoff is labor. With 24 or more feet of joint per square foot, epoxy residue has far more places to hide, and it must come off before it skins. Setters handle that by grouting in small sections (often a few square feet at a time), using the epoxy maker's cleanup kit, and having a second person follow with the wash. If you have never used epoxy, practice on a scrap board of the same mosaic first. The epoxy application guide covers the steps.

Grout color on a mosaic

Because grout covers so much of a mosaic, color choice changes the whole surface, not just the outline. A contrasting grout on a 1 inch hex floor creates a strong honeycomb grid that can look busy across a large room and will show every slightly crooked sheet. A matching grout lets the mosaic read as a texture, hides sheet-to-sheet alignment errors, and keeps attention on any pattern in the tile itself.

Two practical points: in blended mosaics with several tile colors, a mid-tone grout drawn from the most common color usually works best, and in showers, very light grout on a floor mosaic shows soap and mineral staining quickly given how much of it there is. See the grout color guide and test with the color visualizer.

Preparing mosaic joints for grout

Most mosaic grout failures start at setting. Mosaic sheets are thin and the joints narrow, so thinset easily squeezes up between tiles. Grout over squeezed-up thinset is only a skin, and it tends to crack, powder or show as a different color where the mortar shows through.

• Use the right trowel. Mosaics usually call for a small V-notch or square notch trowel (often 3/16 inch V or 1/4 inch square, depending on tile and substrate). Flatten ridges slightly so the mesh beds without flooding the joints.
• Mesh-backed sheets: embed the mesh fully, then rake joints with a toothpick, plastic pick or margin trowel tip while the mortar is soft.
• Paper-faced sheets: set with the paper outward, wet and peel the paper within the time the mortar allows, then adjust tiles and clean joints. Remove all glue residue from the face; it can interfere with grout cleanup.
• Clean to depth. Aim for joints open to at least two thirds of the tile thickness. With 1/4 inch thick mosaics, that leaves very little margin for error.
• Use white mortar under glass and light-colored mosaics, so any mortar that does show reads light, not gray.

Grouting technique for mosaics

1. Mix to a creamy, not runny, consistency. Narrow joints tempt people to add water to make grout flow. Extra water weakens it and causes shading. Pack it in with float pressure instead. See how to mix grout.
2. Float in several directions. Work the float diagonally, then across the other diagonal, so grout fills joints running every way, especially with hex and penny rounds.
3. Strike off hard. Hold the float nearly vertical and pull off as much excess as possible. Less on the face means less washing.
4. Wash with a damp, not wet, sponge. Small tiles can be pulled from the bed or pushed out of line by a heavy hand or soaking sponge. Use light, circular passes and then a straight final pass.
5. Check for low joints and pinholes. Fill them before the grout firms. Mosaics show voids easily because there are so many joints. See grout pinholes and voids.
6. Buff the haze. Use dry microfiber once the surface dulls. Textured mosaics benefit from a soft brush.

For tools that suit small tile, such as narrow floats and fine-cell sponges, see grout tools.

Living with mosaic grout

A 1 to 2 inch mosaic has six to twelve times the joint length of 12x12 tile, and every foot of it has to be kept clean. Cement grout on mosaics in wet areas should be sealed with a penetrating sealer once cured, and resealed on a schedule (see how often to seal grout). Daily drying with a squeegee or towel helps shower floors more than any cleaner. For tough cleaning, use pH-appropriate cleaners and soft brushes; see how to clean grout.