I'm finishing dry-fitting my cbu & will put it in place using thinset as per the manufacturers instructions in the next day or so. I'll be using a 1/4" square-notched trowel (other opinions appreciated). My question is should I work the thinset in between the expansion joints between the different sheets of plywood subfloor to fill in all gaps under the cbu. Is that right? Or won't that defeat the purpose of the expansion joints. Isn't the thinset supposed to get squished into all crevices anyway as it's screwed down - so won't it get squished into the expansion joints anyway? All opinions welcome & much appreciated.