How Much RedGard Do I Need for Shower Walls?
The short answer
A typical three-wall alcove shower has about 88 sq ft (8.2 m²) of wall, and RedGard covers 55 sq ft per gallon at the required two coats - so plan on 2 gallons (7.6 L) for the walls. Waterproofing the shower pan too? The floor needs a heavier film - 40 sq ft per gallon - which pushes a full shower to roughly 3 gallons.
- Shower walls and tub surrounds - 110 sq ft per gallon per coat, two coats = 55 sq ft (5.1 m²) per gallon, done (Custom Building Products TDS-104).
- Shower pan / floor - 80 sq ft per gallon per coat, two coats = 40 sq ft (3.7 m²) per gallon to meet the plumbing-code shower-liner listing (IAPMO).
- Pail sizes - RedGard comes in a 1-gallon (3.78 L) and a 3.5-gallon (13.2 L) pail. For a full shower, the 3.5-gallon pail is usually the buy.
The classic mistake is reading “110 sq ft per gallon” off the label and buying half of what you need. That figure is per coat, and RedGard is a two-coat product for waterproofing.
What a gallon of RedGard actually covers
Custom defines coverage by the finished film thickness, not by the pass of the roller. For waterproofing, the membrane must dry to about a 17-mil film; one coat at 110 sq ft per gallon leaves roughly half that (Custom technical bulletin TB94). Here’s the real per-gallon coverage by use:
| How you’re using it | Rate per coat | Coats | Real coverage per gallon |
|---|---|---|---|
| Shower walls / tub surround (waterproofing) | 110 sq ft | 2 | 55 sq ft (5.1 m²) |
| Shower pan / floor (IAPMO shower liner) | 80 sq ft | 2 | 40 sq ft (3.7 m²) |
| Crack isolation under tile | 100 sq ft | 1 | 100 sq ft (9.3 m²) |
| Moisture vapor barrier | 70 sq ft | 1-2 by vapor load | 70 or 35 sq ft (6.5/3.3 m²) |
Coverage assumes a smooth substrate. Porous cement board drinks more than the chart says, which is why a 10% cushion belongs in the math.
Worked example: a 3 × 5 ft alcove shower
Standard alcove, 3 ft deep × 5 ft wide (0.9 × 1.5 m), membrane running up the walls to 8 ft (2.4 m):
- Wall run: 5 ft back wall + two 3 ft side walls = 11 linear ft.
- Wall area: 11 × 8 = 88 sq ft.
- Add 10% for the niche, the curb, and roller waste: 88 × 1.1 ≈ 97 sq ft.
- Divide by real coverage: 97 ÷ 55 = 1.76 → round up → 2 gallons for the walls.
Doing the pan as well? 3 × 5 = 15 sq ft ÷ 40 ≈ 0.4 gallons. Walls plus pan lands near 2.2 gallons, so buy three 1-gallon pails or one 3.5-gallon pail - the big pail is usually cheaper per gallon, and the leftover handles touch-ups.
👉 The Waterproofing Calculator does this math instantly - enter the floor size and how high the membrane runs up the walls, set the coverage per gallon (55 for RedGard walls, closer to 40 when the pan is a big share of the job), and it returns the area and gallons with the waste cushion built in. It runs the wall band around the full floor perimeter, so on a three-wall alcove the result lands slightly high - treat that as your safety margin. And the coverage field takes any product’s label number, so the same tool works for Hydro Ban, AquaDefense, or whatever membrane is on sale.
Watch-outs
- Two coats is not optional. A single coat is about half the required film thickness for waterproofing. Roll the second coat at right angles to the first.
- Watch the color. RedGard goes on pink and dries to solid red - typically 1 to 1.5 hours, up to 12 hours in cool or humid conditions. Recoat only after it’s fully red, and you can flood test as soon as the final coat has fully dried (TDS-104).
- Mesh the trouble spots. RedGard needs no fabric in the field, but Custom recommends embedding 6 in (15 cm) fiberglass mesh at changes of plane and any gap of 1/8 in (3 mm) or more for extra protection - and the drain detail calls for a 12 × 12 in (30 × 30 cm) piece embedded around the drain flange.
- Don’t overbuild either. Custom caps wet film at 40 mils in all cases - a thicker pour is not extra protection, it’s off-label.
- Mind the temperature. Don’t apply if the surface could drop below 40°F (4°C) within 72 hours of application.
Related
- Waterproofing Calculator - membrane area and gallons for any liquid waterproofing, waste included.
- Flooring tools - the full flooring toolset.
- How much does a bathroom remodel cost - budget the whole bathroom, not just the membrane.
- Half-inch vs five-eighths drywall - pick the right board for the dry walls outside the wet area.