The idea is to make the subfloor flat. By cutting the plywood that way the oposite is achieved the plywood will be more flexible and it will fillow the existing surface on which the subfloor is installed on https://youtu.be/7l6ts1YwnfU

1 Answer 1


The video shows the installer adding thickness under the new flooring material so that the new floor will be level with the existing tile that was 1.5 inches taller (I got that from the video description) . The video was not talking about leveling a wavy floor. The installer was using 3/4" plywood as an underlayment, and as you pointed out, by cutting the kerfs into the plywood, it will follow the waviness (if any) that already exists in the subfloor.

  • The title says leveling the subfloor and then adds a clarification which I missed. However it does not make a lot of sense.I would have used self leveling cement first otherwise you are just copying the uneveness from below
    – MiniMe
    Jul 30, 2022 at 2:15
  • If the floor was not level, I agree with you. If the floor was level, then this will be fine. If you like my answer, please accept it.
    – RetiredATC
    Jul 30, 2022 at 2:49
  • This method is far superior to leveling compound for increasing the height of a large area +(and much cheaper) leveling “cement” doesn't work as well for large areas. The plywood makes a better base that holds up better for any type of flooring. The back cut allows the plywood to adjust to minor deviations in the floor.
    – Ed Beal
    Jul 30, 2022 at 19:23

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