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Unread 10-21-2020, 05:43 PM   #5
Veteran DIYer- Schluterville Graduate

STAR Senior Contributor

Join Date: Jul 2004
Location: Nashua, NH
Posts: 14,205
Two things (other than the possible joist and spacing, which could also be big):
- while that construction adhesive works fine on the top of a joist where you can nail/screw it down and expect it to spread out and fill in gaps, that WILL NOT happen when spread out underneath a sheet. A liquid wood glue, spread like thinset so you get full coverage CAN work, but it's tricky getting things together before the glue starts to set
- D-faces are known to create problems in tiling situations.
- maybe a third, if the glue in the ply itself is not rated as Exposure 1 or EXT, moisture can cause it to delaminate.

Your call, your home. How long do you want it to last? No guarantees either way, but the industry doesn't agree with your choices so far for reason, supported by testing.
Jim DeBruycker
Not a pro, multiple Schluter Workshops (Schluterville and 2013 and 2014 at Schluter Headquarters), Mapei Training 2014, Laticrete Workshop 2014, Custom Building Products Workshop 2015, and Longtime Forum Participant.
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