I am replacing my counter tops with tile. Lowe's suggests using mastic between the plywood & cement board, then securing the cement board with screws. Why is the mastic necessary if the cement board will be screwed down, then mastic on top of it to secure the tiles. This seems like an unnecessary step.
Actually, I'm a bit more old school. I believe that the best way to to a tile countertopis a mud set over plywood with the tarpaper & chicken wire. Then I would install the tile with thinset, depending upon what type of tile you are installing. Mastic is ok, but thinset is really what the pros use. Why? I think its a stronger bond.
Cement boardis ok. It works alright, but ask any old tile guy & he will tell you a mudset base is more stable. If you go with cement board, I don't recall ever putting any mastic between the plywood and the cement board. Some guys still put felt or tarpaper down between the plywood and the cement board to avoid water damage to the plywood. (not a bad idea). I've always gone with screws.
Make sure you do your sink cutout on your plywood before you attach the cement board. Its always easier.
While I do respect the opinions of the post above, I am a firm believer in allowing technology to ease the burden of labor and material cost. The reason for the suggestion of mastic between the plywood comes directly from the Tile Council of North America‘s 2007 handbook for ceramic tile installation. The handbook recommends three different types of installation which are: 1.) Cement mortar (Mud bed) as described in the previous post. 2.) Thin-set application. 3.) Backer Board installation. It is my belief that the thin-set application is the least costly without compromising the strength of substrate. This method of installation is achieved by securing (with screws)two layers of ¾” Plywood then using a cut strip of ¾” plywood to the face edge of the countertop. Note: Set bottom edge of countertop proper distance above drawers, doors, and dish washer allow clearance for movement. I strongly recommend the use of Thin-set mortar as opposed to mastic. Mastic is in fact easier to work with and there is no mixing involved. But it is much more costly and takes much longer to dry. Both types of adhesive will work just as well, however this is my recommendation. PS: Tile trim at the edge of the counter top is normally very problematic. I know at Home Depot and possibly Lowes, they make a oak trim that finishes the edge off very nicely. Good luck, if you have any problems we check these post regularly and will gladly answer any other questions you may have.