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Unread 10-23-2020, 08:03 PM   #11
Veteran DIYer- Schluterville Graduate

STAR Senior Contributor

Join Date: Jul 2004
Location: Nashua, NH
Posts: 14,225
SOme people are adamant that that is a requirement, the thinset manufacturers seem to realize that any thinset that gets in there will pulverize if the sheets move. Gaps on the subflooring are generally required prior to closing the building in, as they can be rained on and the moisture levels can spike while the joists are also drying out. The plywood association actually calls for no gap on underlayment that ends up being installed after the building is after it was closed in and dried out. Subflooring goes in at the beginning, underlayment gets installed just prior to finished materials go on, much later. A small gap doesn't hurt, but it is not critical on a closed building later on.
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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