Replacing plywood underlayment

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eldo

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I’m remodeling my bathroom and taken up all the floor tile. The tile was laid directly on a plywood underlayment that was glued and nails to the subfloor. My plan was to lay ditra under the tile. Should I replace the plywood underlayment and then lay the ditra? Should I be using something else for the underlayment. Should I lay the ditra directly on the subfloor? Should I skip it and just use a backer board over the subfloor? Advice much appreciated.
 
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wwhitney

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Is your subfloor a sheet good (plywood, OSB), or is it dimensional lumber (tongue and groove boards)?

Cheers, Wayne
 

Jeff H Young

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Ditra and Hardi backer or other board is often used I dont know which factors to concider in choosing
 

eldo

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Is your subfloor a sheet good (plywood, OSB), or is it dimensional lumber (tongue and groove boards)?

Cheers, Wayne
Thanks Wayne. It's plywood. I'm not sure how thick but I'm going to check near my drain/overflow cutout.
 

wwhitney

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Ditra, cement board, Hardiebacker, and foam boards like GoBoard are all reasonable substrate options for floor tile. On the board products you generally only need the 1/4" thick version for floor applications, since they are continually supported by the plywood subfloor. [Note that if you had a dimensional lumber subfloor, a layer of plywood as intermediate between the solid sawn wood and the tile backer is generally called for, since dimensional lumber will move more with temperature/humidity changes.]

So the choice of whether to leave the underlayment layer of plywood is up to you, based on its condition and what height you want to net out at. I would probably only leave it if its face is in good condition and (a) it would be a pain to remove or (b) I wanted the extra height. Unless the underlayment plywood is nearly as thick as the subfloor plywood, the underlayment plywood doesn't provide significant structural benefit.

Whatever tile substrate you choose, be sure to read and follow the manufacturer's instructions.

Cheers, Wayne
 

eldo

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Ditra, cement board, Hardiebacker, and foam boards like GoBoard are all reasonable substrate options for floor tile. On the board products you generally only need the 1/4" thick version for floor applications, since they are continually supported by the plywood subfloor. [Note that if you had a dimensional lumber subfloor, a layer of plywood as intermediate between the solid sawn wood and the tile backer is generally called for, since dimensional lumber will move more with temperature/humidity changes.]

So the choice of whether to leave the underlayment layer of plywood is up to you, based on its condition and what height you want to net out at. I would probably only leave it if its face is in good condition and (a) it would be a pain to remove or (b) I wanted the extra height. Unless the underlayment plywood is nearly as thick as the subfloor plywood, the underlayment plywood doesn't provide significant structural benefit.

Whatever tile substrate you choose, be sure to read and follow the manufacturer's instructions.

Cheers, Wayne
Wayne, thank you very much!
 

Jeff H Young

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hardi backer over ply or OSB is common here but youll have to work through details on your particular case.
 

eldo

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Thank you very much folks. I'm settling on throwing down a fresh 1/2" ply layer under the Ditra. I'll have to figure out an elegant way to handle the transition from tile to carpet as the finished tile will be higher than the carpet. Thanks again!
 
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