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ARDEX 8+9 Coverage Calculator: How Many Kits Do I Need?
Enter the area you want to waterproof and pick the substrate. ARDEX 8+9 is a two-part kit, so the calculator counts in gallons of the ARDEX 8 liquid: one convenient kit holds 1 gallon of liquid and a 9 lb bag of powder, one commercial unit holds 3 gallons and a 27 lb bag. The rates come from the ARDEX Americas technical data sheet (content updated 2026-08-09): 100 sq ft per kit for two coats over drywall and about 70 sq ft over concrete. It then picks the kits and commercial units to buy.
ARDEX 8+9 coverage
| Application | Coats | Per gallon, each coat | Per gallon, all coats |
|---|---|---|---|
| Over drywall or backer board: 2 coats, 100 sq ft per kit (per gallon of ARDEX 8) | 2 | 200 sq ft (18.6 m²) | 100 sq ft (9.3 m²) |
| Over concrete: 2 coats, about 70 sq ft per kit (per gallon of ARDEX 8) | 2 | 140 sq ft (13 m²) | 70 sq ft (6.5 m²) |
Source: ARDEX Americas Technical Data Sheet: ARDEX 8+9 Rapid Waterproofing and Crack Isolation Compound, content updated 2026-08-09, read 2026-10-26.
How the calculation works
gallons = area × (1 + waste ÷ 100) × coats ÷ sq ft per gallon per coat
Every coat goes over the whole area, so two coats at 80 sq ft per gallon use as much liquid as one coat at 40. The rate depends on what the membrane is for: the data sheet lists a heavier rate for code-listed waterproofing than for crack prevention alone. The calculator then picks the fewest pails that cover the job without leaving more than one small pail of liquid unused, so a job needing 3 gallons gets one 3.5 gallon pail rather than three 1 gallon pails. Extra passes over corners, seams, drains and pipe penetrations are not included; raise the waste figure if you have many of them.
Worked example
A 100 sq ft area, Over drywall or backer board: 2 coats, 100 sq ft per kit (per gallon of ARDEX 8), with 10% extra: 100 × 1.1 = 110 sq ft. The data sheet calls for 2 coats at 200 sq ft per gallon each, so 110 × 2 ÷ 200 = 1.1 gallons (4.2 L). In the pail sizes on sale, buy 2 × 1 gal convenient kits (2 gal).
ARDEX 8+9 key specs
| Product type | Waterproofing membrane |
|---|---|
| Package | convenient kit (1 gal / 3.78 L ARDEX 8 liquid + 9 lb / 4 kg ARDEX 9 powder) and commercial unit (3 gal / 11.34 L liquid + 27 lb / 12 kg powder) |
| Coverage (data sheet) | convenient kit: 100 sq ft (9.3 m²) for 2 coats over drywall, approx. 70 sq ft (6.5 m²) for 2 coats over concrete; commercial unit up to 300 sq ft (27.9 m²) |
| Kit contents | convenient kit: ARDEX 8 liquid 1 gal (3.78 L) bottle + ARDEX 9 powder 9 lb (4 kg) bag; commercial size: 3 gal (11.34 L) bottle + 27 lb (12 kg) bag |
| Mixing | paintable: the whole liquid unit per bag (1 part liquid to 1 part powder by volume); caulking: about 2/3 of the liquid per bag; no water or additives; pot life up to 45 minutes |
| Film | 2 coats required for waterproofing and crack isolation, second at 90° to the first; total thickness at least 1/32 in (0.79 mm); 3 coats for submerged use |
| Drying | first coat 30–45 minutes; final coat about 1 hour at 70°F (21°C) before tile; flood test 4 hours after the second coat |
| Crack isolation | ANSI A118.12, in-plane cracks up to 1/16 in (1.5 mm) alone or 1/8 in (3 mm) with ARDEX SK MESH; crack bridging of dormant cracks up to 1/8 in with mesh |
| Standards | ANSI A118.10 waterproofing (breaking strength 865 psi, seam strength 48 lb/in); Robinson test extra heavy |
| Tools | 3/8 in nap roller and brush; ARDEX T-2 paddle and high-speed drill; 3/16 x 3/16 in V-notch trowel for a mesh bed over large cracked areas |
| Limits | substrate and air at least 50°F (10°C); not for commercial steam showers, roofing or as exterior primary waterproofing over indoor spaces; mortar over it at most 3/8 in thick |
| Other | gray or white; VOC 0; shelf life 1 year; sold to professional contractors, not through home improvement centers |
What ARDEX 8+9 is
ARDEX 8+9 is a two-part waterproofing and crack isolation membrane from ARDEX Americas. ARDEX 8 is the liquid and ARDEX 9 is a powder made from Portland cement and other hydraulic cements. You mix the two on site and roll or brush the slurry onto floors and walls before setting ceramic tile or stone. Unlike the ready-to-use acrylic membranes, it sets by hydration, so it dries quickly: the first coat is ready for the second in 30 to 45 minutes, tile can go on about an hour after the final coat, and a flood test can start 4 hours after the second coat.
The ARDEX technical data sheet (content updated 2026-08-09) lists it for showers, bathrooms, kitchens, balconies and other wet areas, in place of a shower pan liner, and for submerged uses such as pools with three coats. It meets ANSI A118.10 for waterproofing and ANSI A118.12 for crack isolation, bridging in-plane cracks up to 1/16 inch on its own and up to 1/8 inch with ARDEX SK MESH. It is not for commercial steam showers, roofing, or exterior primary waterproofing over indoor spaces.
What the data sheet says about coverage
ARDEX gives coverage per kit, not per gallon, and it depends on the substrate:
- Convenient kit (1 gallon of ARDEX 8 and a 9 lb bag of ARDEX 9): 100 sq ft (9.3 m²) for two coats over drywall.
- The same kit over concrete: approximately 70 sq ft (6.5 m²) for two coats.
- Commercial unit (3 gallons of ARDEX 8 and a 27 lb bag of ARDEX 9): up to 300 sq ft (27.9 m²).
The commercial unit is exactly three convenient kits of liquid and powder, and its 300 sq ft is three times the 100 sq ft drywall figure. That lets the calculator work in gallons of ARDEX 8: a 1 gallon kit is one unit, the commercial size is three. Two coats over drywall at 100 sq ft per kit means each coat covers 200 sq ft per gallon of liquid; over concrete, each coat covers about 140. The data sheet does not give a separate figure for cement backer board, which is close to drywall in texture, so the calculator uses the drywall setting for smooth boards and the concrete setting for slabs, mortar beds and masonry.
The liquid figure assumes the paintable mix, where the whole bottle goes in with the whole bag. For caulking consistency you use only about two thirds of the liquid per bag, and that thicker material goes around penetrations, corners and floor to wall joints. Any unused caulking mix can be blended back into the remaining liquid for the paintable coats, so it does not waste product, but it does use up some of the kit.
How thick the membrane has to be
Two coats are required for both waterproofing and crack isolation, the second rolled at a right angle to the first, and the finished film must be at least 1/32 inch (0.79 mm) thick. That is about 31 mils. One kit of mixed paintable material spread to that thickness over 100 sq ft works out to roughly the volume of the liquid and powder together, which is why rough concrete, which soaks up more and has more surface area, gets less coverage. If your coats go on thin, you will cover more area than the chart, but the membrane may not reach the minimum thickness. It is safer to follow the chart and check with a wet film gauge than to stretch a kit.
How to use the calculator
Measure every surface that will get membrane. In a shower that means the floor, every wall to the height you are waterproofing, the curb top and both faces, and the inside of any niche or bench. Add those up and enter the total. Pick the substrate, then set a waste figure. Ten percent covers a normal shower; go higher if there are many corners, a linear drain, lots of pipes, or a large cracked area that needs a mesh bed, since the data sheet calls for a first layer applied with a 3/16 x 3/16 inch V-notch trowel under the mesh, which uses a lot more material than a rolled coat.
The calculator then multiplies the area by the two coats and divides by the coverage per coat to get gallons of ARDEX 8. It chooses the fewest packages that cover that amount without leaving more than one convenient kit unused. For 2.5 gallons it picks one commercial unit, not three convenient kits; for 1.2 gallons it picks two convenient kits.
Buying and storage notes
ARDEX sells 8+9 in gray and white. The data sheet says it is intended for trained professional contractors and is not sold by ARDEX through home improvement centers, so you will usually find it at tile distributors. Keep the liquid from freezing, store both parts in a cool, dry place out of the sun, and use them within a year. Install only when the substrate and air are at least 50°F (10°C), and turn off any in-floor heat 48 hours before and after the installation.
Once dry, cover the membrane with mortar within 24 hours so dust does not settle on it. ARDEX limits the mortar over 8+9 to 3/8 inch thick, which is about what a 3/4 x 3/4 inch notched trowel leaves after the tile is set.
FAQ
How many square feet does an ARDEX 8+9 kit cover?
ARDEX's data sheet gives 100 sq ft for the two required coats over drywall and about 70 sq ft over concrete for the convenient kit, which is a 1 gallon bottle of ARDEX 8 and a 9 lb bag of ARDEX 9. The commercial unit is three times the size, 3 gallons and 27 lb, and the front page of the data sheet puts it at up to 300 sq ft. Over concrete, plan on about 210 sq ft per commercial unit.
Why does concrete take more than drywall?
Concrete is rougher and more porous than a drywall or backer board face, so more of the slurry goes into the surface before the film builds up to the required thickness. The data sheet only gives the two figures, 100 and about 70 sq ft per kit, so use the concrete setting for slabs, mortar beds and masonry, and the drywall setting for smooth boards.
How much ARDEX 8+9 do I need for a shower?
Add the floor, the walls you will cover, the curb and any niche. A 3 x 5 ft shower with three walls coated to 7 ft is 15 sq ft of floor and 77 sq ft of walls, 92 sq ft in all, or about 101 sq ft with 10 percent extra. Over backer board that is just over one kit, so buy two convenient kits. If the floor is a mortar bed, figure it at the concrete rate.
Does the coverage include caulking and mesh at corners?
No. The coverage figures are for the two paintable coats over the field. Corners, changes of plane, drains and pipes get caulking-consistency material and ARDEX SK MESH first, and over a large cracked area the mesh is bedded in a layer applied with a 3/16 x 3/16 inch V-notch trowel. All of that uses extra material, so raise the waste figure when there is a lot of detail work or mesh.
Can I use ARDEX 8+9 in a pool or steam shower?
ARDEX lists submerged uses such as swimming pools but requires three coats and asks you to contact its technical service department first. The data sheet gives no coverage figure for three coats; as a rough guide, a third coat adds about half again to the two coat amount. It is not recommended for commercial steam showers.
ARDEX and ARDEX 8+9 are trademarks of their owner. This page is an independent estimate based on the published data sheet; check the bag label before mixing.