What are the advantages and limitations of cementitious backer units (CBUs) for tile installations?

• A. Advantages include rigidity, moisture resistance
• B. Disadvantages include weight, potential for debonding
• C. Both A and B are true
• D. CBUs have no limitations

Answer: (C)

CBUs give a tile installation a stiff, stable substrate, which helps resist substrate movement from everyday loading and prevents cracks from propagating into the tile layer. The cementitious nature also provides moisture resistance compared with some other backers, improving performance in many applications—as long as you use proper waterproofing in areas exposed to water, since CBUs themselves aren’t waterproof. On the downside, their weight makes handling, support requirements, and overall installation more demanding. They can also debond if the substrate moves or if the adhesive bond under the CBU or between the CBU and tile isn’t properly established, especially under moisture or temperature cycling. Balancing these factors, the statement that includes both the advantages and the limitations best captures what CBUs bring to tile installations.