Which Side of the Cement Board Goes Down?

Do-it-yourselfers doing a little research on tile and stone installation likely come across cement board underlayment. Cement board is DIY- and professional-preferred for good reason. Not only does it provide a structurally sound, moisture-proof tile-setting surface, cement board is a miracle of DIY tile installation because it negates the manually laborious wall and floor substrate floating process.

Cement board is an effective shower wall substrate.

Which Side Out

Cement board manufacturers imprint a gridlike pattern on one surface of the board. In addition to giving the do-it-yourselfer proper-spaced nail or screw placing, the pattern indicates the front of the board. Also, cement board typically has a label or manufacturer sticker on the front of the board. The back of cement board is plain, has no manufacturer-defining stickers and is void of the front-featured grid. Always install cement board with the grid facing out.

Wall Installation

Cement board must be at least 1/2 inch thick for wall installation and 1/4-inch cement board is appropriate if 5/8-inch-thick sheathing is present. Manufacturers recommend installing a moisture barrier first -- either heavy-felt construction paper or 4-mil plastic -- locking out water and preventing future moisture issues in wet areas. Affix 1/2-inch cement board to wall studs every 8 inches with either 1 1/2-inch galvanized roofing nails or 1 1/4-inch cement board screws. Also, fasten the cement board at joints and corners.

Floor Installation

The do-it-yourselfer has more flexibility installing plywood floor cement board -- the thinner, easier-to-cut 1/4-inch board is appropriate. Plywood floor underlayment must be 5/8 inch and 3/4 inch if installing a large modular tile -- 12 inches or greater. Avoid lining up cement board joints with plywood joints. Apply a polymer-modified thin-set mortar to the underlayment before installing the board. Attach the cement board throughout the board with 1 1/4-inch cement board screws or 1 1/2-inch galvanized roofing nails. Attach it every four to six inches.

Additional Tips

Cement board contains hazardous materials. Always wear proper eye and breathing protection -- especially while cutting the material. A plumb and level wall and floor underlayment is absolutely required for a quality cement board application. Adjoin cement board sheets with a thin-set mortar-installed mesh tape. Stagger cement board joints to ensure a strong tile-setting surface.