Cracks at Ceramic Floor Tiles over Wood Framed Floors

Ceramic floor tile installed over wood-framed floors are generally more vulnerable to cracking and displacement as compared to tile over concrete installations. This is primarily due to the more flexible nature of wood relatively to a more stable concrete slab. Floor tile are more brittle and thus prone to cracking over more flexible wood framing below.

Wood framing expands and contracts with changes in moisture and temperature. It is also susceptible to deflection. This, while not always being a structural concern, can cause cracking or other failures of brittle floor tile installed above it. For the above reasons, special care should be given to maximize stability of wood framed floors supporting floor tile or other brittle flooring material. This includes minimizing the wood framing’s exposure to moisture, because moisture can increase deflection and contribute to movements from shrinkage and swelling.

Ceramic tiles installed over wood framed floors are usually over a mortar bed, cement boards, or plywood underlayment between the tile and the wood subfloor. These are intended to provide additional stability and isolate, as much as possible, the floor tile from the underlying wood floor structure. The maximum deflection of the sub floor due to live loads should typically not exceed 1/360. This equates to one inch deflection over a 30 foot span.

ADDITIONAL RESOURCES:

TCNA Handbook for Ceramic, Glass, and Stone Tile Installation

ANSI A108/A118/A136.1 – Specifications for the Installation of Ceramic Tile

ANSI A137.1 – Specifications for Ceramic Tile