Sanded, unsanded or epoxy grout: how to choose and how much you need
By Michał Białas · Last updated
Use unsanded grout for joints narrower than 1/8 in, sanded grout for joints 1/8 in and wider, and epoxy where stains or water are a concern. How much you need depends on the tile size, joint width and tile thickness: small tile with wide joints can need five or six times more grout per square foot than large tile.
The three types
| Unsanded | Sanded | Epoxy | |
|---|---|---|---|
| Joint width | Narrower than 1/8 in (3 mm) | 1/8 in (3 mm) and wider | Most widths; check the product |
| Strength in wide joints | Can shrink and crack | Good; sand stops shrinkage | Very good |
| Stain and water resistance | Needs sealing | Needs sealing | High; no sealing needed |
| Working time | Easy | Easy | Short; mix small batches |
| Watch out for | — | Can scratch polished stone and glass tile | Hard to clean off tile faces once set |
| Typical density | About 1.6 kg/dm³ | About 1.6 kg/dm³ | About 1.5 kg/dm³ |
Polymer-modified cement grouts and flexible grouts sit between these. Use a flexible, polymer-modified grout over radiant floor heating and wood subfloors, and epoxy in kitchens, showers and commercial floors where stains and cleaning chemicals are part of daily life.
The grout formula
Grout fills the joints, so the quantity is the joint length per square meter × joint width × joint depth × the grout density. Joint depth is taken as the tile thickness. With everything in millimeters:
G (kg/m²) = (L + W) ÷ (L × W) × joint width × tile thickness × density
L and W are the tile length and width. The grout calculator applies this, adds 15% for what stays in the bucket, on the float and in the sponge, and picks the combination of bags with the least left over — or the cheapest one, if you enter prices.
Worked examples
Example 1 (feet): 12 × 10 ft room, 12 × 12 in tile, 3/8 in thick, 1/8 in joints
- In millimeters: tile 304.8 × 304.8, thickness 9.5, joint 3.2.
- G = (304.8 + 304.8) ÷ (304.8 × 304.8) × 3.175 × 9.525 × 1.6 = 0.32 kg/m² (0.065 lb/sq ft).
- Room: 11.15 m² × 0.32 = 3.5 kg; + 15% = 4.1 kg = 9.0 lb.
- Joint 1/8 in → sanded grout. Buy one 10 lb bag.
Example 2 (meters): 4.0 × 3.0 m room, 600 × 600 mm tile, 10 mm thick, 2 mm joints
- G = (600 + 600) ÷ (600 × 600) × 2 × 10 × 1.6 = 0.107 kg/m².
- Room: 12 × 0.107 = 1.28 kg; + 15% = 1.47 kg → one 2 kg bag.
- Joint 2 mm → unsanded grout.
- In epoxy (density 1.5): 1.2 kg + 15% = 1.38 kg → one 2.5 kg kit.
Example 3 (meters): 5 m² of 100 × 100 mm mosaic, 6 mm thick, 3 mm joints
- G = (100 + 100) ÷ (100 × 100) × 3 × 6 × 1.6 = 0.576 kg/m² — more than five times the large-tile floor above.
- Total: 5 × 0.576 = 2.88 kg; + 15% = 3.31 kg → two 2 kg bags.
Choosing by room
- Living areas and bedrooms: sanded or unsanded by joint width; seal cement grout in hallways and entries.
- Kitchens: epoxy, or a stain-resistant polymer-modified grout, sealed.
- Showers and wet rooms: epoxy, or cement grout over a proper waterproofing membrane — grout itself is not waterproof (see waterproofing a bathroom floor).
- Radiant heating and wood subfloors: flexible, polymer-modified grout.
- Polished marble, glass and soft stone: unsanded or epoxy to avoid scratches.
Color, sealing and upkeep
Grout color changes the look of a floor more than most people expect. A grout close to the tile color hides small irregularities and makes a floor look calmer; a contrasting grout outlines every tile and shows every uneven joint. Mid-tone grays hide dirt best on floors. Mix a small sample and let it dry, because wet grout looks darker than it will be.
Cement grout is porous. A penetrating sealer, applied once the grout has fully cured and renewed every year or two in busy areas, keeps out dirt and spills. Epoxy grout needs no sealer. Clean grouted floors with a pH-neutral cleaner; strong acids attack cement grout and some stone.
Grouting checklist
- Wait until the thinset has cured: usually about 24 hours for standard thinset; less for rapid-setting products.
- Remove spacers and clean thinset out of the joints.
- Mix small batches; epoxy and rapid grouts set fast.
- Pack the joints with a rubber float held diagonally to the joints.
- Clean with a barely damp sponge once the grout firms up; don’t wash it out of the joints.
- Use flexible sealant, not grout, at inside corners and where the floor meets the walls.
- Seal cement grout once it has fully cured, if the product calls for it.
Frequently asked questions
Can I use sanded grout for 1/16 in joints?
It is hard to pack sand into joints that narrow, and the result is often weak. Use unsanded or epoxy grout for joints narrower than 1/8 in.
Why do I need so much grout for mosaic?
Small tiles mean many more joints per square foot. A square meter of 100 mm mosaic has 20 m of joints; a square meter of 600 mm tile has just over 3 m.
Is epoxy grout worth the extra cost?
In kitchens, showers and entryways it often is: it resists stains and doesn’t need sealing. In bedrooms and living areas, cement grout is usually fine.
Is grout depth really the tile thickness?
For estimating, yes. Real joints are slightly shallower where thinset squeezed up, which the 15% waste covers.