Installing Cement Backer Board
DEAR TIM: I have a ceramic-tile job coming up and want to use cement backer board. I have never installed this product before, and wonder if it is really worth it. It seems hard to work with and I am tempted to just use a water-resistant drywall. Is cement backer board really worth the trouble? What tips can you share to make the job go easier and faster? Jackie L., Pleasant Hill, CA
DEAR JACKIE: There are all sorts of different tile backer board products out there. Some are cement-based, some are gypsum-based and others have a mix of ingredients. The cement-backer-board products can be a little tough to work with during the installation process, but in my opinion, they pay you back in spades for the effort.
I am not against new technology when it comes to building products. There are countless examples of where a new product is much better than existing products. Plywood and oriented strand board (OSB) are excellent examples of this. Before plywood and OSB, carpenters used to deal with smaller pieces of wood that were not as dimensionally stable as plywood and OSB. Plywood and OSB also makes very good use of wood as a natural resource.
But when it comes to tile and what it should be applied to, I feel that cement might be the standard to a large degree. Cured cement is not damaged by water. You can immerse a piece of cement board in water for an indefinite amount of time, and it will never fall apart.
There are tens of thousands of ceramic-tile installations all over the world that are hundreds of years old that are still in great shape. Almost all of these are installed directly over concrete or some cement-based material. Many older homes still standing in the USA have ceramic tile firmly attached to cement stucco that was applied over wire mesh by true craftsmen.
All that being said, there are indeed other high-performance backer boards for ceramic tile. This past summer I decided to test a newer one in my daughter's bathroom. It has a rough fiberglass face and a waterproof gypsum core. It was easier to cut than cement backer board, but the installation of the product to the wood studs was the same as far as I was concerned.
If you want a gorgeous ceramic-tile job, you need to be sure the backer board is in the same plane and the walls are perfectly plumb. In the old days, the tile setters installing the wet cement stucco took the time to get the stucco perfectly plumb and flat, even if the wall studs were crooked, bowed or bent.
With modern cement backer board, you must get the framed walls perfectly plumb and flat. Since the cement backer board is thin and a uniform thickness, when you attach it to the studs, it simply conforms to the shape of the stud wall. This means twisted, out-of-plumb frame walls will lead to twisted, out-of-plumb ceramic tile. No one wants that.
The cement backer board can be cut with a circular saw with an abrasive blade, but that process creates clouds of choking dust, and can cause great damage to the saw motor. You can score the cement backer board with a hand tool that has a carbide tip. You make numerous passes along the cut line, and then apply pressure to the other side of the cement backer board along the scored line. It usually snaps the backer board in two quite nicely along the desired line.
I also recommend a water-resistant barrier between the backer board and the wall framing. You can put overlapping layers of asphalt felt paper or go with a large sheet of plastic commonly used for a vapor barrier. This layer helps protect the wood framing from wood rot in that rare case where water would soak through the cement backer board.
When installing the cement backer board, I like to leave a 1/8-inch gap between pieces. This gap is then filled with pure silicone caulk before the ceramic tile is installed. I never allow the cement board to rest on top of a bathtub edge. If water gets to the cement board, capillary attraction can cause water to wick up into the cement backer board. I always leave a 1/4-inch gap between the top of the tub and the bottom edge of the backer board.
The cement backer board can be screwed or nailed to the wood framing. Always follow the instructions printed by the manufacturer. I use hot-dipped ring-shanked nails if I am nailing. Corrosion-resistant screws can also be used. You need to make sure the cement backer board will never fall off the wall at a later date. Inferior fasteners can cause catastrophic failure if they rust.