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Choosing backer board for tile projects

Q: I'm getting ready to buy backer board for a ceramic tile project. There are different types out there, and I'm a little confused. Which backer boards do you use and which do you avoid? Also, please share any backer board installation tips.

A: I've installed lots of concrete backer board for years, all with good results. The concrete is unaffected by any water that manages to get behind the ceramic tile. But these concrete products are heavy, problematic to cut and can wick water, causing wood rot.

Recently I've been experimenting with some alternative backer boards. The most recent one I've worked with has a water-resistant gypsum core with a fiberglass mat backing and a blue waterproof coating on the side that the tile adheres to. This material is code approved and recommended by a leading ceramic tile association. I find this material far easier to work with than the cement backer boards. And I definitely don't miss the small pieces of sand and grit that scratch tub finishes.

Using this particular product also saves a step in the building process. If you use cement backer board, you have to install a separate moisture barrier between the board and any wood it is attached to. Since the concrete can absorb and wick moisture, the barrier prevents wood rot if the backer board gets saturated.

I witnessed firsthand what happens when cement backer board is installed without a moisture barrier. Last month I demolished a 25-year-old bathroom that had waterlogged cement board in the shower. Because no water barrier was installed, the bottoms of some of the wall studs were beginning to show water damage.

When I first got into the construction business nearly 35 years ago, a moisture-resistant drywall was the backer board of choice. It had a green paper so you could distinguish it easily from traditional drywall. Millions of square feet of this was installed in bathrooms, some by me, until we in the building trades discovered it didn't do too well. Water passed through grout joints and eventually caused the green paper to fall apart. Virtually every building code now shuns this product for use in wet areas. I would never install this product behind tiles that were subject to water splashing on them.

As you prepare to install your ceramic backer board, the first thing to do is stop and read all the instructions. The product that I used with the bright blue coating had instructions attached to each sheet.

Also don't underestimate the importance of using the correct fasteners when installing the backer board on walls. The combined weight of the board and the tiles you'll attach to it is considerable. Use screws instead of nails — and not just drywall screws. You can usually find special backer board screws that have oversized, bugle-shaped heads that securely fasten the board to wood or metal studs. Be sure the screws are coated so they don't rust. It's also important to drive the screws flush with the surface of the board. Don't allow them to tear the coated facing of the board.

If you're installing your backer board in a shower or tub, don't allow the board to come into contact with the concrete shower pan or the tub ledge. I prefer to hold the backer board one-quarter inch off tub ledges and one-half inch off a concrete substrate in a poured shower. Holding the board up prevents the edge from sitting in any water.

Tim Carter is a licensed contractor. To view previous columns or tap into his archive of information and sources of building materials, go to You can write to Tim Carter at P.O. Box 36352, Cincinnati, OH 45236-0352.


Using backer board

• Cutting backer board, especially gypsum-core backer board, is done with a simple razor knife. Score the surface with the razor, then snap the board, creating a clean line. Then use the razor to cut the fiberglass backing. It's the same procedure used to cut regular drywall.

• Take your time to make sure that wall studs are plumb and in the same plane before you install backer board. These products conform exactly to what you fasten them to. If you want your tile to go in easily, the backer board must be plumb and flat.

• Make sure the backer board you use on floors is attached to a sound subfloor. Screw down the wood subfloor to the floor joists before installing the backer board. If the floor seems springy or bouncy, you'll likely end up with cracked tile. Be sure to install the backer board in a bed of cement thinset mortar to ensure there are no hollow spots or voids in between the backer board and the wood subfloor.

Choosing backer board for tile projects 08/14/09 [Last modified: Friday, August 14, 2009 4:30am]
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