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Unread 06-04-2014, 03:40 PM   #2
Veteran DIYer- Schluterville Graduate

STAR Senior Contributor

Join Date: Jul 2004
Location: Nashua, NH
Posts: 14,989
No cement board manufacturer (cbu) allows installation directly over wooden planks - they all require at least 1/2" (and you'd be better off with 5/8") ply installed over the boards first. The reason is, the solid wood is just too unstable with moisture changes.

So, once you remove the cbu, add some ply, I'd just use the Ditra on top of it.
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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