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What is cement board?

Cement board is a cement-based panel used as a backing surface behind tile and other finishes. PNNL’s Building America guide describes a cementitious core strengthened by glass mats on both sides. For a shower project, ask how the wall manages water: ordinary cement board resists water but is not itself waterproof.

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By InstaBids editorial team with AI research agents. Updated

What this means for your home project

  1. Ask the contractor to identify the waterproofing or drained barrier in the shower wall assembly; ordinary cement board alone is not waterproof. Source: Building America Solution Center (PNNL), read 2026-10-31.
  2. Ask how the cement-board edge meets the shower pan without allowing water to wick into the backing. Source: U.S. Department of Energy, read 2026-10-31.
  3. Ask which seam treatment the proposed board’s manufacturer specifies, and include that treatment in the written scope. Source: Building America Solution Center (PNNL), read 2026-10-31.
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Is cement board waterproof?

Ordinary cement board resists water without serving as the waterproof layer. PNNL distinguishes it from panels specifically manufactured as waterproof products; the shower needs a water-management plan. “Unless specifically manufactured as a waterproof product, cement board is water resistant but not waterproof.” Source: Building America Solution Center (PNNL), read 2026-10-31.

What is cement backer board intended to support?

Cement backer board supplies the backing surface behind a finish. PNNL places it behind tiled or segmented tub and shower enclosures, where joints can expose the backing to moisture. “Install cement board or an equivalent moisture-resistant backing material on walls behind tub and shower enclosures composed of tile or panel assemblies with caulked joints.” Source: Building America Solution Center (PNNL), read 2026-10-31.

What Is Cement Board Made Of?

The cement board described by PNNL has a cementitious core with reinforcing glass mats on both faces. That construction describes this backer material; other panel materials have different cores. “Appropriate materials include cement board which has a cementitious core and glass mats on both sides to strengthen the board.” Source: Building America Solution Center (PNNL), read 2026-10-31.

Can you use cement board outside?

Exterior suitability depends on the particular board. The JLC field guide says some cementitious backerboard types suit exterior work, so ask for the proposed panel’s documented application before specifying it outdoors. “Both types come in a variety of thicknesses and types, some (but not all) of which are suitable for exterior use.” Source: Journal of Light Construction, read 2026-10-31.

Does the water resistant cement board installed overlapping/hiding the edge of a shower pan absorb water in time?

Yes, direct contact can let backerboard draw water upward. DOE’s tub-and-shower guide describes this as wicking and explains why the board-to-pan transition deserves attention in the project scope. “The direct contact between the shower pan and backerboard could lead to the backerboard wicking up any water that gets past the finish surround.” Source: U.S. Department of Energy, read 2026-10-31.

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