Unsanded Grout: Narrow Joints, Delicate Tile and Its Real Limits

Unsanded grout is cement grout made without sand aggregate, so it is smooth and fine enough to pack into joints narrower than 1/8 inch. Use it for tight joints, wall tile, glass and polished stone that sand could scratch. Avoid it in joints wider than about 1/8 inch, where it shrinks, cracks and sags.

What makes unsanded grout different

Unsanded grout (also sold as "non-sanded" or "wall grout") contains portland cement, very fine mineral fillers, pigments and additives. Some products include extremely fine aggregate that is not sold as "sand", and the line between unsanded and fine-aggregate high-performance grout has blurred. What defines the category in practice is particle size: everything in the bag is fine enough to slip into a 1/16 inch joint.

Unsanded grouts are tested to the same standards as sanded ones. Basic products meet ANSI A118.6; polymer-modified versions meet ANSI A118.7 with lower water absorption and better color uniformity. Under ISO 13007-3 they are CG1 or CG2.

The shrinkage problem: why it fails in wide joints

Every cementitious grout shrinks a little as it cures and dries. In sanded grout, the sand grains carry most of the volume and only the paste between them shrinks. In unsanded grout, the whole joint is paste. The shrinkage percentage is higher, and in a wide joint it adds up to a visible movement.

Three failure patterns follow when unsanded grout goes into joints wider than its rating:

• Center-line cracking. A hairline crack runs down the middle of the joint, often appearing within the first few days.
• Edge separation. The grout pulls away from one tile edge, leaving a thin gap that collects water and dirt.
• Dishing and slump. The grout settles below the tile surface as it loses water, leaving concave joints. On walls it can sag before it sets.

These look similar to structural cracking, so diagnose before you blame the grout. Why grout cracks explains how to tell shrinkage cracks from movement and deflection problems.

Where unsanded grout belongs

The tile-specific guides go deeper: grout for glass tile, grout for mosaic tile, and kitchen backsplash grout.

Small tiles mean a lot of joint

Unsanded grout is often chosen for mosaics, and mosaics are mostly joint. The table below is geometry only: cubic inches of open joint per square foot of tiled area at full tile depth, before waste. The joint area analysis shows the same effect as a percentage of the visible surface.

A 1 x 1 inch mosaic with 1/16 inch joints needs more grout per square foot than 12 x 12 tile with 1/4 inch joints (about 2.2 cubic inches). In mosaics, the grout is a big part of what you see, which is why grout color matters so much on them.

Mixing and packing unsanded grout

The general method is in how to mix grout. Unsanded grout has a few quirks.

• It feels drier than it is. Fine powder absorbs water slowly and the mix can look stiff for the first minute. Mix fully and slake before deciding it needs more water. Usually it does not.
• Mix smaller batches. Wall tile is grouted slowly, and unsanded grout stiffens in the bucket. Batches you can use within the pot life on the TDS avoid the temptation to retemper with water.
• Use a softer float on glass or delicate faces. A soft rubber or margin float reduces the risk of scuffs. Some installers prefer a foam float for very small mosaics.
• Pack, then strike. Work the float diagonally, pressing grout into the joints in two directions. Then strike off excess with the float edge held nearly upright.
• Do not dig the joints out. Narrow joints have little grout to spare. An aggressive sponge pass easily pulls 1/16 inch joints below the tile surface.

Joint depth matters more in thin joints

Narrow joints are often clogged with thinset that squeezed up during setting. If only the top 1/16 inch of the joint is open, the grout is a thin skin that pops out under traffic or cleaning. Clear the joints to at least two-thirds of the tile thickness before the thinset cures; it is far easier than raking cured mortar later. When to grout after tiling covers the timing.

Polished stone and glass: safe from scratches, not from stains

The main reason to choose unsanded grout on polished marble is to protect the polish. It does that well. But porous stone can absorb pigment and water from the grout along the joint edges, leaving a darker "picture frame" around each tile. Many stone setters seal the stone before grouting (when the sealer manufacturer allows it), choose a grout color close to or lighter than the stone, and use white unsanded grout under white or translucent marble. See grout for natural stone for stone-specific precautions.

With clear or translucent glass, the grout color shows through the tile from behind as well as in the joint. White or a color matched to the glass is the safe default, and epoxy is popular because its color is more uniform from batch to batch.

Unsanded grout on floors

Unsanded grout is allowed on floors within its joint width range, and many floors with rectified tile and 1/16 inch joints use it successfully. The tradeoff is abrasion: the surface is all cement paste, so grit underfoot wears it down faster than a sanded joint, and it can become rough and harder to clean. On a busy kitchen or entry floor, consider a fine-aggregate high-performance cement grout, urethane grout or epoxy grout that is rated for 1/16 inch joints. The floor grout guide compares them.

Sealing and care

Basic unsanded grout is absorbent and stains easily, especially in white or pale colors on backsplashes. A penetrating sealer applied after the cure time on the TDS improves stain resistance. Polymer-modified versions absorb less, but sealing is still common in kitchens. Clean with a neutral cleaner; acidic cleaners etch cement grout over time.