I am planning on replacing the tile on the countertop in my kitchen. Whoever did the counter before used 1/2" thick plywood, 1" thick particle board, and a layer of some type of fiberglass sheet over the plywood and particle board layers. I was hoping to rip all the fiberglass and particle board off and add 1/2" thick backer board to the 1/2" thick plywood. A few places have said 3/4" plywood is best. Should I add another 1/4" sheet of plywood?
Leah -- Boston, Ma
Leah, most professionals recommend using ¾-inch exterior grade plywood as a foundation for ceramic tile countertops. The thickness helps support the weight of the tiles, but also works to reduce movement that can cause the grout to crack. Whenever a heavy mixer or pan full of water is placed on the countertop, thin plywood may flex slightly under the weight.
That being said, I have heard of some tile countertops being constructed with only ¼-inch plywood and ½-inch backer board. I'm sure they looked fine when first finished, but don't know how they held up to long term use.
Another issue to keep in mind is the overall height of the cabinets and countertops in your kitchen. There may be a reason why the previous owner made the existing tops so thick such as matching the top surface up with a high range or other appliance.
Using just the ½-inch plywood might suffice, but if it were my kitchen, I'd add the ¼-inch plywood just to be safe. It isn't much extra work since you already plan to install new backer board and the material is fairly inexpensive. The last thing you want is to have your beautiful new tile countertops have their grout lines begin to crack -- especially when the only good solution is to install thicker plywood.