ceramic tile to wood floor threshold
You should treat all the seams, (subfloor, underlayment and CBU as directed by the thinset and CBU manufacturers. Some want you to keep thinset out of the underlayment seams, while others want you to fill them. Filling those seams will not necessarily prevent those seams from compressing, they will compress with latex modified thinset in there.
You're still supposed to install expansion joints in the field in all installations if they're large enough or under certain conditions such as direct sunlight and wet rooms. Expansion joints are placed in the CBU and directly over it in the tile.
Until a few years ago Hardie used to tell us to install an expansion joint in the center of any room both ways if the room was 15 ft. or larger in any direction, and where the room makes an "L". This was rarely done since most people didn't have or didn't read the directions anyway. Today's directions don't even bring up the subject of field expansion joints. Touchy subject I'm sure.
tishimself, that type of installation requires additional joints every 8-12 ft. in both directions.
Tile 4 You LLC Troy, MI
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