If you're installing tile on a wall or a countertop, you'll need a base beneath the tile that will hold up to moisture without losing integrity. Cement board, available in 4-foot by 8-foot panels, is standard for use as a tile backer board. Durock, a name brand cement board manufactured by USG Corporation and sold throughout the United States, is suitable as a backer board for tile. After the Durock panels are in place, you must fill the joints before you can install the tile.
Wipe dust and debris from the joints between the Durock panels. Scrape away hardened clumps of excess glue that may remain around the seams with a putty knife.
Cut fiberglass mesh tape to fit in a single layer over every joint where the panels meet, but do not overlap the tape. It's OK if it's an inch or two short in spots. The tape is self-adhesive and will stick to the Durock panels. Press and smooth the tape firmly in place.
Mix powdered latex-reinforced cement mortar with water as directed on the package in a clean plastic bucket. Use a drill fitted with a paddle attachment to blend the mortar until smooth.
Fill an oblong mud pan about half full with the mortar mix and cover the remaining mortar with a tight-fitting lid to keep it from drying out.
Scoop up about 1/2 cup of mortar mix with the blade of a 6-inch taping knife and smooth it over the Durock joints, pressing the mortar mix through the holes in the fiberglass mesh tape and deep into the seams between the panels.
Wipe excess mortar from the surface of the joints, leaving a smooth, flat seam.
Continue filling the joints until all the seams contain mortar and the top of the seams are smooth. Let the mortar dry completely before installing tile.