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I have two sections of flooring that are currently uneven by about 1/4". One side is 3/4" OSB, and the other is 3/4" Plywood. Both sides are screwed and glued onto joists. I'm planning on putting cement board across both sides to prep for tile after that.

floor layer diagram

  • Should I use 1/4" Plywood to bring the two sides to level? Is there something else to use instead - like self-leveling compound?
  • Do I screw the plywood into the joists or just into the underlying subfloor? Screw every 6 inches - or more or less?
  • Do I use glue between the plywood and the OSB? Or something else between the layers?
  • Your plan sounds good to me. I think construction adhesive between the ply and OSB is a good idea. I don't think you have to go crazy with the screws if you backer screws penetrate the OSB as well. Self leveling compound sounds messy and unnecessary since the 1/4 will make up for it and the OSB is otherwise level. – Gary Bak Dec 6 '18 at 22:54
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I would use 1/4inch Luan panels and install without adhesive. Just install to manufacturers specs. This is typically to lay it down and use 1/4 inch crown staples, 1 inch long, every 6 inches along the perimeter and 8 inches in the field.

A few things to note:

  1. Make sure the subfloor is secured before using the Luan.
  2. Make sure there are no protrusions from old screws/nails.
  3. Clean the subfloors well. A shop vac is a good method.
  4. Make sure you stagger the seams by half of a sheet (or manufacturer specs). If using a full sheet to start one run, use a half sheet for the next run. Then back to a full sheet for the 3rd.
  5. Be sure to check for and avoid over and under penetration of the staples.
  6. Make some 1/4 in spacers and use those to keep the luan 1/4 from the walls.
  • This is one of the very few places that I'd use luan, aside from craft projects. It's not a high-quality product and it's prone to staining adjacent materials, but it'll do fine as a filler layer. – isherwood Dec 7 '18 at 16:11

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