A 25 lb bag of Custom’s Polyblend Plus sanded grout covers about 461 sq ft of 12 by 24 inch tile with 1/8 inch joints, by its chart. At a 1/4 by 3/8 inch trowel, a 50 lb bag of thinset covers 55 to 70 sq ft, by the Custom, LATICRETE and MAPEI data sheets.
Tile thickness
Joint width
Trowel (square notch)
How much grout and thinset?
For this tile and joint: Custom’s Polyblend Plus chart, about 5.4 lb (461 sq ft per 25 lb bag); LATICRETE’s PERMACOLOR Select chart, about 4.7 lb (429 sq ft per 20 lb). That’s 1 bag of 25 lb or 1 box of 7 lb. Thinset at a 1/4 × 3/8″ trowel: 2 bags of 50 lb.
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How the grout math works
Grout fills the joints around each tile, so the amount follows the joint’s length, width and depth. ARDEX prints the formula on its ARDEX-FLEX FL grout sheet: add the tile’s length and width, multiply by the joint’s width and depth and by a coverage figure, then divide by the tile’s length and by its width. In inches, per square foot of floor or wall, the joints hold 144 × (length + width) ÷ (length × width) × tile thickness × joint width cubic inches. Smaller tiles mean more joint per square foot, and so does a wider joint.
ARDEX’s coverage figure for its FL grout, 1.75, works out to 0.0632 lb per cubic inch. To turn the volume into pounds we use 0.065, the highest weight per cubic inch that Custom’s Polyblend Plus chart implies under this formula, so the answer is never under Custom’s or LATICRETE’s chart for a tile they list. For mosaic with wide joints it runs well over them, up to 2.25 times Custom’s figure for 1 inch tile at 1/2 inch joints. Where your tile and joint are on a chart, the answer shows the chart’s own figure beside it.
| Tile (inches) | Joint | Custom Polyblend Plus, 25 lb | LATICRETE PERMACOLOR Select, 20 lb |
|---|---|---|---|
| 2 × 2 × 1/4 | 1/8″ | 96 sq ft | 83 sq ft |
| 6 × 24 × 3/8 | 1/8″ | 279 sq ft | 258 sq ft |
| 12 × 12 × 3/8 | 1/8″ | 348 sq ft | Not listed |
| 12 × 24 × 3/8 | 1/8″ | 461 sq ft | 429 sq ft |
| 12 × 24 × 3/8 | 1/4″ | 234 sq ft | 215 sq ft |
| 24 × 24 × 3/8 | 1/8″ | 688 sq ft | 643 sq ft |
Custom calls its chart one for estimating purposes, and LATICRETE calls its coverage approximate.
Thinset by trowel
| Square-notch trowel | Custom VersaBond and others | LATICRETE 253 Gold, 254 Platinum | MAPEI Ultraflex 2 |
|---|---|---|---|
| 1/4 × 1/4″ | 85 to 95 | 80 to 95 | 75 to 90 |
| 1/4 × 3/8″ | 60 to 67 | 60 to 70 | 55 to 65 |
| 1/2 × 1/2″ | Not listed | 35 to 40 (254 Platinum) | Not listed |
Custom’s figures are the same for VersaBond, FlexBond, CustomBlend and MultiSet. Custom’s ProLite (30 lb) and LATICRETE’s MULTIMAX Lite (25 lb) are lightweight mortars that each cover what a 50 lb bag does.
Custom’s sheets say mortar must cover at least 80% of the tile’s back in dry areas and 95% in wet areas and outdoors, and that large tiles, tiles with deep patterns on the back and ungauged stone may need a bigger notch and back-troweling. Custom doesn’t recommend a 1/2 inch square-notch trowel, which it says makes tiles harder to bed.
Joint widths and bag sizes
Custom’s Polyblend Plus Sanded fills joints from 1/8 to 1/2 inch and comes in 25 lb bags and 7 lb boxes; for joints up to 1/8 inch, Custom points to its NonSanded grout. LATICRETE’s PERMACOLOR Select fills joints from 1/16 to 1/2 inch, from 10 and 20 lb bags of base.
Custom’s Polyblend Plus sheet says the powder causes severe skin burns and serious eye damage, and that breathing its dust over time may cause lung damage or cancer. It says to wear nitrile gloves, safety glasses and an N95 respirator. LATICRETE’s PERMACOLOR Select sheet warns of the same burns and silica dust.
Which thinsets list a plywood floor
Thinset on plywood