Cement Backer Board (CBU)

Category: infrastructure

A rigid, water-stable substrate panel composed of portland cement and fiberglass mesh, used behind wet-area tile installations.

Cement Bonded Units (CBUs) replace traditional drywall behind showers and tubs. While CBUs will not rot, disintegrate, or lose structural strength when exposed to moisture, they are still porous; they require an additional liquid or sheet membrane layer to form a true waterproof barrier.

Common Examples

• The framing contractor fastened the half-inch cement backer board panels using specialized corrosion-resistant alkaline screws.
• Standard drywall mud will dissolve behind a shower; always tape and seal cement backer board joints using polymer-modified thinset mortar.