View Single Post
Unread 06-14-2019, 07:51 PM   #12
Veteran DIYer- Schluterville Graduate

STAR Senior Contributor

Join Date: Jul 2004
Location: Nashua, NH
Posts: 13,201
The reason for two layers is to prevent the joints over the joists from bending upwards, potentially producing a stress crack. Adding a second layer, properly offset, prevents that first layer seam from projecting upwards enough to preserve the natural stone with potentially numerous internal imperfections. A manufactured tile is more consistent and can usually handle a single layer..

Think of the ends of the panels as little levers...a weight in the middle between the joists makes the edge of the joist act like a fulcrum, pushing the end up slightly even with the construction adhesive considering it's only attached by typically about 3/4" overlap.

IOW, use two layers to mask that joint's movement.
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.
jadnashua is offline   Reply With Quote