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<> Coverage figures assume a 50 lb bag, a clean flat substrate, and correct trowel technique — combed in one direction, tile pressed and slid perpendicular…
With these inputs:
| Result | Value |
|---|---|
| Thinset needed | 2 bags |
| Coverage per 50 lb bag | 75 sq ft |
| Area to set | 120 sq ft |
| Back-butter allowance | None |
| Effective area | 120 sq ft |
Buy one extra bag — partial bags absorb moisture and go off quickly once opened.
<> Coverage figures assume a 50 lb bag, a clean flat substrate, and correct trowel technique — combed in one direction, tile pressed and slid perpendicular to the ridges to collapse them. Mosaic and small tile: 3/16" V-notch Up to 12": 1/4" × 1/4" square notch 12"–16": 1/4" × 3/8" Large format 18"+: 1/2" × 1/2" plus back-buttering Back-buttering large tile adds roughly 30–40% more mortar but is required to hit the 95% coverage that warranties and wet areas demand. Modified vs unmodified is the decision people get wrong. Polymer-modified thinset is the default for porcelain, large format and most floors. Unmodified is correct over an uncoupling or waterproofing membrane, because the membrane is impervious and a modified mortar sandwiched between two non-porous layers cannot cure properly. The membrane manufacturer's instructions override every general rule here. Mix to a peanut-butter consistency, let it slake for 5–10 minutes, then re-mix without adding water. Thinset stays workable for about 45 minutes on a warm day, so mix half a bag at a time until you know your pace. Once the mortar is sized, the grout calculator covers the other half of your setting materials, and the tile cost calculator rolls both into a project total. Setting large format? The large-format calculator sizes the tile order to match. Not sure which mortar to buy? Read modified vs unmodified thinset ; bedding a floor in board first? The cement backer board calculator counts sheets and screws. Which notch to spread it with? The tile trowel size calculator matches the trowel to your tile size.
With a 1/4 x 3/8 inch notched trowel, about 75 sq ft per 50 lb bag — so two bags for 100 sq ft. Large-format tile with a 1/2 inch notch needs three.
About 0.5 lb per sq ft with a 1/4 x 1/4 inch notch (a 50 lb bag covers ~95 sq ft), 0.67 lb with 1/4 x 3/8 inch (~75 sq ft), and 1.1 lb with a 1/2 inch notch (~45 sq ft). Back-buttering large tile adds roughly 10–15% on top.
Use polymer-modified for porcelain and most floors. Use unmodified when setting over an uncoupling membrane or when the membrane manufacturer specifies it — check the membrane instructions first.
No. Thinset is an adhesive, not a leveler. Fix dips with a self-leveling underlayment or patch compound before tiling, or the tile will crack.
Walk on it after 24 hours and grout after 24–48 hours. Full cure is 28 days, which matters before a shower is used or heavy furniture is moved back in. Cold or humid conditions extend all of these.
Match the notch to the tile: 3/16 inch V-notch for mosaic, 1/4 x 1/4 inch square for tile up to 12 inches, 1/4 x 3/8 inch for 12–16 inch tile, and 1/2 x 1/2 inch plus back-buttering for anything 18 inches and larger.
Need the whole roof at once? The free roofing calculator works out roof area, squares, shingle bundles, underlayment, drip edge, ridge cap and installed cost from one set of measurements.