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Mapei Ultraflex 2 Coverage Calculator: How Many Bags?
Enter your area and trowel notch to see how many 50 lb (22.7 kg) bags of Ultraflex 2 polymer-modified thinset to buy. Coverage figures come straight from MAPEI's US technical data sheet.
Mapei Ultraflex 2 coverage
| Trowel notch | US | Metric |
|---|---|---|
| 1/4" x 1/4" x 1/4" square notch (6 x 6 x 6 mm square notch) | 75–90 sq ft | 7–8.4 m² |
| 1/4" x 3/8" x 1/4" square notch (6 x 10 x 6 mm square notch) | 55–65 sq ft | 5.1–6 m² |
Source: MAPEI Technical Data Sheet: Ultraflex 2 (USA, English), MK 3002823 (26-1628), edition date May 6, 2026, read 2026-10-16.
How the calculation works
bags = area × (1 + waste ÷ 100) ÷ coverage per bag, rounded up
The manufacturer gives a coverage range for each trowel size because the real figure depends on the tile back, the substrate and how much mortar ends up in the ridges. This calculator divides by the low end of the range, so the number it tells you to buy should not leave you short. If you back-butter large tiles, plan for coverage at or below the low end.
Worked example
A 120 sq ft floor with a 1/4" x 3/8" x 1/4" square notch trowel and 10% extra: 120 × 1.1 = 132 sq ft. At the low end of the coverage range (55 sq ft per bag) that is 132 ÷ 55 = 2.4 bags, so buy 3. That is 150 lb of powder.
Mapei Ultraflex 2 key specs
| Product type | Thinset mortar |
|---|---|
| Bag size | 50 lb (22.7 kg) |
| Mixing water per bag (max) | 6 US qt (5.68 L) |
| Mixing water | 5–6 US qt (4.73–5.68 L) per 50 lb bag |
| Working time after mixing | about 2 hours |
| Open time | 30 minutes (at 73°F / 23°C, 50% RH) |
| Pot life | more than 2 hours |
| Time before grouting | 16–24 hours |
| Traffic | light traffic after 24 hours, heavy traffic after 7 days |
| Application temperature | 40°F–95°F (4°C–35°C) |
| Standards | ANSI A118.4E and A118.11; ISO 13007 C2EP1 |
| Bag sizes | 50 lb gray and white (US); 10 lb and 25 lb in Canada and Puerto Rico only |
| VOC content | 0 g per L |
| Shelf life | 1 year at 73°F (23°C) |
What Ultraflex 2 is for
Ultraflex 2 is MAPEI's standard polymer-modified thinset for ceramic, porcelain and natural-stone tile. Because the polymer is already in the powder, you mix it with plain water; no liquid latex additive is needed for the uses the data sheet lists. It meets ANSI A118.4E and A118.11 and is classed C2EP1 under ISO 13007, where the P1 part refers to its bond to plywood.
The data sheet covers most residential floors and walls, inside and out. In commercial work the scope is narrower: interior floors and walls, and exterior floors, but not exterior commercial walls. Suitable substrates include concrete cured at least 28 days, block and brick, mortar beds, cement backer board, interior drywall in dry areas, VCT and cutback residue (interior only), existing tile (interior only), and MAPEI's own uncoupling, crack-isolation, sound-reduction and waterproofing membranes.
It is not for pools, spas or anything under water, and for severe freeze/thaw exposure MAPEI points you to a mortar mixed with a liquid latex additive instead. Skip it for moisture-sensitive stone such as green marble, agglomerate tile and resin-backed tile, and keep it off OSB, hardwood flooring, metal and substrates that contain asbestos. Over gypsum-based patch or leveler, prime first. For light-colored or translucent stone, use the white version.
Trowel size and how many bags you need
The US data sheet lists coverage for two notches only, both square: 1/4 x 1/4 inch gives 75 to 90 sq ft per 50 lb bag, and 1/4 x 3/8 inch gives 55 to 65 sq ft. That makes Ultraflex 2 a natural fit for small and mid-size tile, such as wall tile, mosaics on a mesh back and the common 12 x 12 inch floor tile.
The calculator defaults to the 1/4 x 3/8 inch notch because it is the usual choice for floor tile and gives the more cautious bag count. It uses the low end of each coverage range and rounds up to whole bags, so for 100 sq ft plus 10% waste at that notch you would buy 2 bags (110 ÷ 55 = 2.0).
If your tile is large or not flat enough for a 3/8 inch notch to reach full contact, this data sheet gives no coverage figure for a bigger trowel, and you should not guess one from the numbers above. MAPEI's large-and-heavy-tile version, Ultraflex 2 LT, lists 1/2 x 1/2 inch and 3/4 inch U-notch coverage and allows a thicker embedded bed.
Whatever the trowel, the real target is contact: more than 80% mortar coverage on both tile and substrate indoors, and more than 95% outside and in wet areas. MAPEI notes you may need to back-butter to get there. Lift a tile now and then to check; if the back is bare in spots, change your technique or the notch before you run out of mortar.
Mixing, timing and protection
For a 50 lb bag, pour about 5 to 6 US quarts (4.73 to 5.68 L) of clean water into the bucket first, then add the powder while mixing slowly. Use a low-speed drill at about 300 rpm with a cross-blade or box mixer, mix until smooth and lump-free, let it stand 5 minutes, and remix. Avoid long mixing. If it stiffens in the bucket, remix it without adding water or powder.
The mix stays workable for about 2 hours. Open time on the floor is about 30 minutes at 73°F and 50% humidity, and less in heat or wind, so spread only what you can set before it skins over. Grout after 16 to 24 hours. Keep light traffic off for 24 hours and heavy traffic for 7 days, and protect exterior work from frost and rain for 7 days. Over nonporous surfaces like membranes or old tile, expect setting to take longer.
Install only between 40°F and 95°F (4°C and 35°C), and clean tools and tile with water while the mortar is still fresh.
Mistakes that leave you short
- Using the high end of the coverage range. On a rough slab or with textured tile backs, you will often land at the low end or below.
- Forgetting the mortar used for back-buttering. The coverage table only counts the notched coat on the substrate.
- Measuring only the open floor and missing closets, the toe-kick area or a shower bench.
- Using the Ultraflex 2 LT water amount. The LT version takes more water per bag (6.5 to 7.5 quarts); standard Ultraflex 2 takes 5 to 6. Extra water weakens the bond.
- Expecting a 10 or 25 lb bag at a US store. In the US the data sheet lists only 50 lb bags; the smaller sizes are sold in Canada and Puerto Rico.
FAQ
How much does a 50 lb bag of Ultraflex 2 cover?
MAPEI lists 75 to 90 sq ft with a 1/4 x 1/4 inch square notch and 55 to 65 sq ft with a 1/4 x 3/8 inch square notch. Actual coverage varies with the substrate profile and the tile, so this calculator uses the low end of each range.
Can I use Ultraflex 2 with a 1/2 inch trowel for large tile?
MAPEI's US data sheet only gives coverage for 1/4 x 1/4 and 1/4 x 3/8 inch notches, so there is no official figure for bigger trowels. For large-format tile that needs a 1/2 inch notch, MAPEI's Ultraflex 2 LT data sheet does list larger notches; see our Ultraflex 2 LT calculator.
How much water goes into a 50 lb bag?
About 5 to 6 US quarts (4.73 to 5.68 L) of clean potable water. Pour the water in first, add the powder while mixing slowly, let it slake 5 minutes, then remix. If it stiffens, remix without adding more water.
How long before I can grout over Ultraflex 2?
The data sheet gives 16 to 24 hours at 73°F (23°C) and 50% humidity. Cold weather and nonporous surfaces such as membranes or existing tile can stretch that, so check that the tile is firm before grouting.
Can Ultraflex 2 go over plywood?
Yes, for interior residential and light commercial floors and countertops in dry conditions, over Group 1 exterior-grade plywood (CC-plugged or better). It is not for OSB, hardwood flooring or metal.
MAPEI and Mapei Ultraflex 2 are trademarks of their owner. This page is an independent estimate based on the published data sheet; check the bag label before mixing.