Comparing Backer Boards for Shower and Wet Area Tile

How to choose the right substrate for moisture-prone spaces

In tiled wet areas—showers, tub surrounds, locker rooms, and spa walls—the backer board is the unsung hero. While tile and grout create the finish, it’s the substrate beneath that determines long-term performance, waterproofing success, and resistance to mold or structural degradation.

With multiple product categories now in play—cement board, foam board, fiber cement, glass-mat panels—procurement leads and tile contractors need to evaluate beyond just cost. The right choice depends on moisture exposure, wall load, build speed, and compatibility with membranes.

Key Types of Tile Backer Boards for Wet Areas

Cement Backer Board (e.g., CBU)

The most widely used wet-area substrate, cement boards are made of cement and reinforcing fibers. They are water-resistant—not waterproof—and require a liquid or sheet membrane over the surface for showers and tub surrounds.

Foam Backer Boards

Lightweight and 100% waterproof, foam boards are made from extruded polystyrene or polyiso and coated with a bonding layer. They’re easier to cut, ideal for fast installs, and often used in curbless shower systems or niches.

Fiber Cement Boards

Similar in use to standard cement board but typically denser. They resist mold and moisture and offer a hard, stable surface for heavy tile assemblies, but like cement board, they require surface waterproofing.

Glass-Mat Panels

Gypsum core panels faced with fiberglass mats and water-resistant coatings. Lighter and easier to handle, but best used in areas with intermittent—not direct—water exposure unless paired with a waterproofing system.

Performance Considerations

Waterproof vs. Water-Resistant: Cement and fiber cement resist water but don’t block it. Foam boards are inherently waterproof.

Weight and Handling: Foam and glass-mat boards are easier to transport and install, especially in high-volume or multi-unit projects.

Compatibility with Tile Adhesives and Membranes: Not all boards work with all types of thinsets or waterproofing systems. Always check manufacturer specs.

Code and Fire Compliance: Some commercial projects require non-combustible substrates or fire-rated assemblies—foam boards may not meet these needs without additional layers.

Best Use by Application

Commercial showers: Cement or foam boards with a full membrane system

Hotel tub surrounds: Glass-mat panels in combo with a liquid-applied waterproofing membrane

Spa and locker room walls: Foam board where speed and waterproofing are priorities

High-rise bathrooms: Fiber cement when structural performance and reduced deflection are needed

Procurement and Installation Tips

Bundle backer board with compatible fasteners, tape, and waterproofing materials

Clarify if a vapor barrier is needed behind the board (varies by climate and wall type)

Confirm screw spacing, thinset requirements, and curing times based on substrate

Offer on-site guidance to prevent membrane gaps, screw blowouts, or improper transitions

Why It Matters

Backer board selection is one of the highest-leverage decisions in wet-area tile performance. The wrong board can lead to:

Membrane failure and moisture intrusion

Mold growth behind walls

Delamination of tile or grout cracking

Costly warranty claims or room shutdowns

For distributors and tile contractors, guiding customers to the right board system—based on project type, installation method, and schedule—adds real value and reduces risk.

In wet area tile, what’s underneath is what holds it all together. Choose wisely, build confidently.