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Mapei Ultraflex 2 LT Coverage Calculator: How Many Bags?
Enter your area and trowel size to see how many 50 lb (22.7 kg) bags of Ultraflex 2 LT large-tile mortar to buy. Coverage figures come straight from MAPEI's technical data sheet.
Mapei Ultraflex 2 LT 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 |
| 1/2" x 1/2" x 1/2" square notch (12 x 12 x 12 mm square notch) | 38–45 sq ft | 3.5–4.2 m² |
| 3/4" x 9/16" x 3/8" U-notch (19 x 14 x 10 mm U-notch) | 25–30 sq ft | 2.3–2.8 m² |
Source: MAPEI Technical Data Sheet: Ultraflex 2 LT (Canada, English), MK 3000399 (24-3266), edition date November 20, 2024, 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 1/2" x 1/2" x 1/2" square notch trowel and 10% extra: 120 × 1.1 = 132 sq ft. At the low end of the coverage range (38 sq ft per bag) that is 132 ÷ 38 = 3.47 bags, so buy 4 (at the high end, 45 sq ft per bag, 3 would be enough). That is 200 lb of powder.
Mapei Ultraflex 2 LT key specs
| Product type | Thinset mortar |
|---|---|
| Bag size | 50 lb (22.7 kg) |
| Mixing water per bag (max) | 7.5 US qt (7.1 L) |
| Mixing water, standard (nonsag/nonslump) | 6.5–7.5 US qt (6.15–7.10 L) per 50 lb bag |
| Mixing water, over MAPEI sheet/peel-and-stick membranes | 7.5–8 US qt (7.10–7.57 L) per 50 lb bag |
| Embedded thickness range | 3/32"–1/2" (2.5–12 mm) |
| Open time | 30 minutes (at 73°F / 23°C, 50% RH) |
| Pot life | more than 2 hours |
| Time before grouting | walls 8–16 hours, floors 24 hours |
| Application temperature | 40°F–95°F (4°C–35°C) |
| Standards | ANSI A118.4HET and A118.11; ISO 13007 C2TE |
| Colors | Gray, white |
| Shelf life | 1 year in the unopened bag at 73°F (23°C) |
When Ultraflex 2 LT is the right mortar
Ultraflex 2 LT is MAPEI's polymer-modified "large and heavy tile" version of Ultraflex 2. The LT formula is nonsag on walls and nonslump on floors, and it is rated for bond coats up to 1/2 inch (12 mm) thick after the tile is embedded. That extra build is the reason to choose it: big porcelain panels and plank tiles are rarely perfectly flat, and a thicker, stiffer bed fills the gap under the middle of the tile without the tile sinking or the edges lipping.
The data sheet lists it for most interior and exterior residential floors, walls and countertops, including wet areas, and for MAPEI uncoupling, waterproofing, crack-isolation and sound-reduction membranes. It meets ANSI A118.4HET and A118.11 and is classed C2TE under ISO 13007.
MAPEI also lists where not to use it: pools, spas and other areas under water; severe freeze/thaw exposure; moisture-sensitive stone such as green marble; resin-backed or agglomerate tiles; and unstable substrates like OSB, hardwood flooring or metal. Over gypsum-based patch or leveler, prime first.
Choosing the trowel, and why it decides the bag count
Trowel size changes coverage far more than anything else. Going from a 1/4 x 1/4 inch notch to a 1/2 x 1/2 inch notch roughly halves what a bag covers (75–90 sq ft down to 38–45 sq ft), so pick the trowel before you buy.
- 1/4 x 1/4 inch square: small, flat tile, roughly up to 8 inches. Not what this product is designed for, but the coverage is listed.
- 1/4 x 3/8 inch square: common for 12 x 12 and similar mid-size tile.
- 1/2 x 1/2 inch square: typical starting point for large-format tile, which is why the calculator defaults to it.
- 3/4 x 9/16 inch U-notch: very large or uneven tile and stone where you need the full 1/2 inch embedded bed.
These are rules of thumb, not the spec. The spec is contact: more than 80% mortar coverage on both tile and substrate indoors, and more than 95% in wet and exterior areas. Set a tile, pull it up, and look. If the back is not covered, go up a notch or back-butter, and plan for more bags.
Mixing and timing on the job
For the normal nonsag mix, MAPEI calls for about 6.5 to 7.5 US quarts of water per 50 lb bag. Mix at low speed (about 300 rpm), let it slake 5 minutes, then remix; if it stiffens in the bucket, remix without adding water. Working time is generous, with 30 minutes open time and more than 2 hours pot life at 73°F, but heat and wind shorten open time, so spread only what you can cover before the surface skins over.
Plan the schedule too: grout walls after 8 to 16 hours and floors after 24 hours, keep foot traffic off for 24 to 48 hours, general traffic for 72 hours and heavy traffic for 7 days.
Common mistakes that run you short
- Measuring only the open floor and forgetting closets, the area under the vanity toe-kick, or a shower bench.
- Using the high end of the coverage range. On textured slabs or with cupped tile you will often land at the low end; this calculator already uses it.
- Forgetting back-butter mortar on large tile. It is not in the table.
- Adding extra water to stretch a bag. A soupy mix sags and loses bond; stay within about 6.5 to 7.5 quarts per bag, and use the 7.5 to 8 quart mix only over MAPEI sheet or peel-and-stick membranes as the data sheet describes.
- Picking the wrong color. It comes in gray and white; for light-colored or translucent natural stone MAPEI recommends white, so buy every bag in the same color up front.
FAQ
How much does a 50 lb bag of Ultraflex 2 LT cover?
MAPEI lists 75 to 90 sq ft with a 1/4 x 1/4 inch square notch, 55 to 65 sq ft with 1/4 x 3/8 inch, 38 to 45 sq ft with 1/2 x 1/2 inch, and 25 to 30 sq ft with a 3/4 x 9/16 inch U-notch. Real coverage depends on the substrate and the tile back.
What trowel should I use with Ultraflex 2 LT for large tile?
Pick the notch that gives full contact: MAPEI asks for more than 80% mortar contact indoors and more than 95% in wet or exterior areas. For large-format porcelain that is often a 1/2 x 1/2 inch notch plus back-buttering, but lift a tile early to check rather than relying on the trowel size alone.
How much water goes into one bag?
About 6.5 to 7.5 US quarts (6.15 to 7.10 L) for the standard nonsag mix. Over MAPEI uncoupling, sheet waterproofing or peel-and-stick membranes the data sheet allows about 7.5 to 8 quarts (7.10 to 7.57 L).
How thick can Ultraflex 2 LT be applied?
The data sheet gives an embedded (after the tile is set) thickness range of 3/32 to 1/2 inch, or 2.5 to 12 mm. It is not a mortar-bed or leveling product for anything thicker.
Does back-buttering change how many bags I need?
Yes. The coverage table is for the notched coat on the floor only. Back-buttering adds a thin skim to every tile, so plan on reaching the low end of the coverage range or below, and keep an extra bag on hand for big jobs.
MAPEI and Mapei Ultraflex 2 LT are trademarks of their owner. This page is an independent estimate based on the published data sheet; check the bag label before mixing.