I’m tiling an upstairs bathroom. The floor is plywood, and I’m hesitant about using Hardie backer board because the height of the floor will be too high. Can you tile directly to plywood with thinset?

—Chris

Hi Chris,

While you can lay tile directly over a concrete slab using thin-set adhesive, don’t make the mistake of applying tile directly to a plywood subfloor. No matter how firm the subfloor; the plywood will expand and contract at a different rate as the tile, causing cracks to develop in the grout lines or tiles over time.

On a plywood subfloor, you need either a layer of cement backer board or an underlayment membrane, like Custom Building Products’ Wonderboard and RedGard, between the subfloor and tile for the thin-set adhesive to achieve a good bond.

While I prefer using 1/2” cement backer board over a plywood subfloor, you may be able to get by with 1/4” backer board instead. Even if you use a waterproof underlayment membrane, the floor will still be either 1/4″ or 1/2” higher than the subfloor, plus the thickness of the tile and adhesive.

When applying cement backer board over a plywood subfloor, be sure to adhere the two surfaces together with thin-set adhesive; and screw the cement backer board down with special screws that countersink into the backer board, such as Backer-On screws available at The Home Depot.

Good luck with your project,

Editorial Contributors
avatar for Danny Lipford

Danny Lipford

Founder

Danny Lipford is a home improvement expert and television personality who started his remodeling business, Lipford Construction, at the age of 21 in Mobile, Alabama. He gained national recognition as the host of the nationally syndicated television show, Today's Homeowner with Danny Lipford, which started as a small cable show in Mobile. Danny's expertise in home improvement has also led him to be a contributor to popular magazines and websites and the go-to source for advice on everything related to the home. He has made over 200 national television appearances and served as the home improvement expert for CBS's The Early Show and The Weather Channel for over a decade. Danny is also the founder of 3 Echoes Content Studio, TodaysHomeowner.com, and Checking In With Chelsea, a décor and lifestyle blog.

Learn More