Shower Waterproofing Systems Compared

Schluter Kerdi

Kerdi is a thin polyethylene sheet membrane with fleece laminated to both sides. It bonds directly to cement board or Kerdi-Board with unmodified thinset. The fleece gives the thinset something to grip on both sides, creating a fully bonded waterproof layer across every surface.

It has been around long enough to have a strong track record and Schluter's system is well thought out. The Kerdi-Band corner strips, Kerdi-Drain flange integration, and Kerdi-Board substrate all work together as a complete system, which takes some of the guesswork out of transitions and details.

• Excellent at corners and seams when installed correctly
• Integrates with Schluter's drain and niche products
• Requires unmodified thinset only. Modified thinset prevents proper bonding and voids the warranty
• Sheet application takes time to do well, especially on outside corners

Schluter Kerdi-Board

Kerdi-Board is an extruded polystyrene foam panel with Kerdi fleece laminated to both faces. It serves as both the substrate and the waterproofing layer in one product. You set it on the studs, tape and thinset the seams, and you are essentially done with waterproofing before you ever apply a separate membrane.

It is lightweight, easy to cut, and very fast to install compared to cement board. The foam core also gives you something to anchor into for niches and shelving without adding blocking. For new construction or full gut remodels, it is a strong option that saves real time.

• Substrate and waterproofing combined into one product
• Lighter and faster to install than cement board
• Good for custom niches and shelves. Anchors directly into the foam
• More expensive than cement board plus a separate membrane

Go Board (Johns Manville)

Go Board is made by Johns Manville, not to be confused with Wedi Board, which is a separate product from a different manufacturer. Go Board is made from extruded polystyrene with a fiberglass mat on both faces and is fully waterproof right out of the box. Seams and corners are taped and thinsetted just like Kerdi-Board.

Go Board works with both modified and unmodified thinset as a substrate, which gives more flexibility on the job. It is slightly more rigid than some other foam boards, which some installers prefer for wall tile.

Note on floor use: Go Board works well for standard mosaic or small-format tile on shower floors. For large-format tile (12x24 or larger) on a shower floor, a mud bed is a better substrate. Large-format tile needs a very firm, consistent base that foam cannot fully provide.

• Compatible with modified or unmodified thinset (as a substrate)
• Fully waterproof panel, no separate membrane needed
• Good alternative to Kerdi-Board at a similar price point
• Not the best choice under large-format floor tile

Wedi Board (Wedi)

Wedi Board is made by Wedi, a German company. It is extruded polystyrene with a polymer-modified cement coating on both faces, which gives it more surface hardness than plain foam boards. Wedi has its own line of sealants, screws, and joint tape that are designed to work as a system.

The cement coating makes Wedi feel more substantial underfoot and on walls, and it bonds well with most thinsets including modified. It is one of the more premium options and is popular in high-end shower builds. Like Go Board, Wedi foam panels work best with standard or small-format tile on shower floors. For large-format tile (12x24 or larger) on a shower floor, a mud bed is the stronger choice.

• Cement-coated faces are more rigid and impact resistant than plain foam
• Works with modified thinset
• Wedi's proprietary sealant at seams creates a robust waterproof joint
• Among the more expensive panel options on the market

RedGard

RedGard by Custom Building Products is a liquid-applied waterproofing membrane. You roll or brush it onto cement board, skim-coated drywall, or concrete in two coats. It starts out pink and turns a solid red when it is dry and at the correct thickness. That color change is a useful feature: it tells you where you have gaps in coverage.

RedGard is fast, straightforward, and does not require seaming or embedding anything. It is a good choice for installers who are more comfortable with a brush than with laying sheet membrane, and it works well in showers that do not have complicated geometry.

Critical note on corners and seams: Apply a second coat over all corners, and embed fabric mesh tape into the wet first coat at every corner and seam before the second coat goes on. A liquid membrane that is not reinforced at corners is the most common point of failure. The membrane at a flat wall surface is fine. The corner is where thermal movement, substrate flex, and water pressure all converge. Fabric reinforcement at every corner is not optional.

• Easy to apply. No seams, no fabric to embed in flat areas
• Color-change indicator shows dry coverage
• Works on cement board, concrete, and masonry
• Corners and seams must be reinforced with fabric mesh tape before the second coat
• Two coats needed, with cure time between

HardieBacker + Membrane

HardieBacker is cement board, not a waterproof product on its own. It is important to be clear about that. It is an excellent tile substrate: dimensionally stable, resistant to mold and rot, and it does not deteriorate from water contact the way drywall does. But water passes right through it.

In a shower, HardieBacker needs a waterproofing membrane applied over it, whether that is RedGard, Kerdi sheet, or another liquid or sheet system. Used correctly as part of a complete system, it is a proven and reliable substrate. Used alone, it is not sufficient.

• Excellent tile substrate: flat, stable, and durable
• Not waterproof on its own. Requires a membrane over it
• Lower cost than foam board systems
• Heavier and harder to cut than foam-based backers
• Widely available and familiar to most installers