CBU (Cement Backer Unit)

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CBU (Cement Backer Unit)

What is CBU (Cement Backer Unit)?

CBU (cement backer unit) is a rigid, moisture-resistant panel used as a tile substrate in wet and high-moisture areas.

Description

A CBU, or cement backer unit, is a rigid panel made from cement and reinforcing fibers used as a substrate for tile installations. It provides a stable, durable surface that resists moisture, making it ideal for areas exposed to water or humidity.

In construction, CBUs are commonly installed behind ceramic tile, porcelain tile, and stone finishes in bathrooms, showers, kitchens, and laundry rooms. Unlike drywall, cement backer units do not deteriorate when exposed to moisture, helping prevent tile failure and mold-related issues.

Proper installation of CBU is essential to system performance. Panels must be securely fastened, seams taped with alkali-resistant mesh, and integrated with waterproofing membranes when required. While CBUs are water-resistant, they are not fully waterproof on their own and must be part of a complete moisture management system.

FAQs

  • What is a CBU used for?

    CBU is used as a tile backing surface in wet or moisture-prone areas such as showers and tub surrounds.

  • Is CBU waterproof?

    CBU is water-resistant but not waterproof; additional waterproofing is typically required.

  • Where should CBU be installed?

    It is commonly installed on walls, floors, and countertops under tile in bathrooms, kitchens, and utility spaces.

  • Can CBU be used on floors?

    Yes, CBUs are often used as underlayment for tile floors to provide a stable base.

  • How is CBU different from drywall?

    CBU resists moisture and provides better tile support, while drywall can degrade when exposed to water.

Fun Fact

Cement backer units were developed to solve a common failure point in tile installations—moisture-damaged drywall hiding behind otherwise perfect-looking tile.

CSI Code

09 30 00

NAHB Code

930