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Mapei Keraflex Plus Coverage Calculator: How Many Bags?
Enter your area and trowel notch to see how many 44 lb (20 kg) bags of Keraflex Plus large-and-heavy-tile mortar to buy. Coverage figures come straight from MAPEI's US technical data sheet, which rates them per 44 lb bag.
Mapei Keraflex Plus 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: Keraflex Plus (USA, English), MK 3000019 (24-3020), edition date October 1, 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 176 lb of powder.
Mapei Keraflex Plus key specs
| Product type | Thinset mortar |
|---|---|
| Bag size | 44 lb (20 kg) |
| Mixing water per bag (max) | 6.2 US qt (5.87 L) |
| Bag size | 44 lb (20 kg), gray or white |
| Mixing water, nonsag/nonslump | 5.7–6.2 US qt (5.39–5.87 L) per 44 lb bag |
| Mixing water, over MAPEI membranes | 6.2–6.6 US qt (5.87–6.25 L) per 44 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 | 3 hours |
| Time before grouting | walls 8–16 hours, floors 24 hours |
| Traffic | no light traffic for 24–48 hours, general traffic after 72 hours, heavy traffic after 7 days |
| Application temperature | 40°F–95°F (4°C–35°C) |
| Standards | exceeds ANSI A118.4HET and A118.11; ISO 13007 C2TEP1 |
| VOC content | 0 g per L |
| Shelf life | 1 year in the unopened bag at 73°F (23°C) |
What Keraflex Plus is for
Keraflex Plus is MAPEI's polymer-modified large-and-heavy-tile mortar. It is nonsag on walls and nonslump on floors, so big porcelain and stone stay where you put them, and it is rated for bond coats up to 1/2 inch (12 mm) thick after the tile is embedded. MAPEI describes it as "extra smooth" and built with what it calls Easy Glide and High-Transfer Technology, which in practice means a creamy mix that spreads easily and wets the back of the tile well. The data sheet also calls it ideal for edge-leveling clip systems, which most large-format installs use today.
It exceeds ANSI A118.4HET and A118.11 and is classed C2TEP1 under ISO 13007: improved cementitious adhesive (C2), low vertical slip (T), extended open time (E) and normal adhesion to plywood (P1).
MAPEI lists it for most interior and exterior residential floors, walls and countertops in dry and wet areas, including tub surrounds and showers; most interior and exterior commercial floors and countertops; interior commercial walls; and exterior-grade plywood. It works with ceramic, porcelain, quarry tile, pavers, Saltillo, manufactured stone and most marble, granite and natural stone.
The 44 lb bag: read this before you compare prices
Keraflex Plus comes in a 44 lb (20 kg) bag, not the 50 lb bag most thinsets use. MAPEI's coverage table is written per 44 lb bag, so the calculator above already counts real bags and you do not need to scale anything.
Where people go wrong is comparing it with other products. MAPEI's data sheet for Ultraflex 2 LT lists the same four coverage ranges (75–90, 55–65, 38–45 and 25–30 sq ft), but per 50 lb bag. So for the same trowel, a bag of either product is rated to cover about the same floor even though one weighs 6 lb less. Compare price per bag against coverage per bag, not price per pound. And if you are shopping for a 50 lb mortar such as LATICRETE 254 Platinum or Custom VersaBond-LHT, use that product's own table.
Choosing the trowel
The notch size changes the bag count more than anything else. Moving from a 1/4 x 1/4 inch notch to a 1/2 x 1/2 inch notch roughly halves what each bag covers, from 75–90 sq ft down to 38–45 sq ft.
- 1/4 x 1/4 inch square: small, flat tile and mosaics on walls.
- 1/4 x 3/8 inch square: common for mid-size tile around 12 x 12 inches.
- 1/2 x 1/2 inch square: the usual starting point for large-format tile, so it is the calculator's default.
- 3/4 x 9/16 inch U-notch: very large or heavy tile and stone where you need most of the 1/2 inch embedded bed.
Those are habits, not the rule. The rule in the data sheet is contact: more than 80% mortar contact to both the tile and the substrate for interior work, and more than 95% for exterior and wet areas, which may mean back-buttering. Key a thin coat into the substrate with the flat side of the trowel first, comb the ridges in one direction parallel to the tile's short side, then push each tile back and forth across the ridges to collapse them. Pull a tile now and then and look at the back.
Mixing and timing
For the normal nonsag/nonslump mix, MAPEI calls for about 5.7 to 6.2 US quarts of water per 44 lb bag; over MAPEI membranes, about 6.2 to 6.6 quarts. Water goes in the bucket first, then the powder, mixed at about 300 rpm with a cross-blade or spiral paddle until smooth. Let it slake 5 minutes and remix. If it stiffens later, remix without adding water.
At 73°F and 50% humidity you get 30 minutes of open time and 3 hours of pot life. Heat, sun and wind shorten open time, so spread only what you can cover before the surface skins. For scheduling, the data sheet gives 8 to 16 hours before grouting walls and 24 hours before grouting floors, then says not to walk on or grout the tile for at least 24 to 48 hours. Keep general traffic off for 72 hours, heavy traffic for 7 days, rain for 72 hours and freezing for 21 days. Install between 40°F and 95°F.
Where not to use it
- Pools, spas and anything under water, or exterior commercial facades.
- Moisture-sensitive stone such as green marble, agglomerate tile, resin-backed tile, and clear or translucent glass tile.
- OSB, hardwood flooring, metal or substrates containing asbestos.
- Gypsum-based patch or leveler without a primer first.
- Severe freeze/thaw exposure, where MAPEI suggests a mortar mixed with a liquid latex additive instead.
Large-tile mortars are not a fix for an uneven floor. Flatten the substrate first, then use the mortar only for the bond coat.
Common mistakes that run you short
- Measuring only the open floor and forgetting closets, thresholds and the area behind the toilet.
- Planning on the top of the coverage range. Rough concrete and cupped tile eat mortar, which is why the calculator uses the low end.
- Back-buttering every large tile without adding mortar for it. The coverage table is for the notched coat only.
- Using a 50 lb product's coverage numbers for this 44 lb bag, or the reverse.
Add 10% for waste on simple rooms and 15% or more for diagonal layouts, lots of cuts or very large tile, and keep one spare bag rather than stopping halfway through a floor.
FAQ
How much does a bag of Keraflex Plus cover?
MAPEI rates coverage per 44 lb (20 kg) bag: 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. This calculator uses the low end of each range.
Why is Keraflex Plus sold in 44 lb bags instead of 50 lb?
That is simply the package MAPEI lists for it in the US data sheet. What matters for buying is coverage per bag, and MAPEI's coverage table is already written per 44 lb bag, so you do not need to adjust anything. Just do not mix up its numbers with those of a 50 lb product.
How much water goes into one bag?
About 5.7 to 6.2 US quarts (5.39 to 5.87 L) for the normal nonsag/nonslump mix, or 6.2 to 6.6 quarts (5.87 to 6.25 L) when setting over MAPEI membranes. Mix at low speed, let it slake 5 minutes, then remix without adding more water.
Can Keraflex Plus be used for large-format tile?
Yes. It exceeds ANSI A118.4H for large and heavy tile, is nonsag on walls and nonslump on floors, and is rated for bond coats up to 1/2 inch (12 mm) after the tile is embedded. It will not correct an uneven floor, so the substrate still has to meet flatness requirements first.
When can I grout after setting tile with Keraflex Plus?
The data sheet gives 8 to 16 hours on walls and 24 hours on floors at 73°F (23°C) and 50% humidity, and its protection section says not to grout or walk on the tile for at least 24 to 48 hours. Cold, humid conditions or nonporous surfaces like membranes stretch these times.
MAPEI and Mapei Keraflex Plus are trademarks of their owner. This page is an independent estimate based on the published data sheet; check the bag label before mixing.