I used to have trouble with large flat forms made from Dave's . Another potter and I split a ton of this white fine groged Dave's many years ago. Its now long gone and I'm back to my 10 tons of regular Daves a year and have not seen any cracking with large forms in years.
I make large bowls and a few platters with it. The big stuff has slowed down in terms of sales past years and just recently is picking back up.
I'm off to Anacortes Wa. Art show mostly with van full of small stuff this week.
For flat large pressed forms I use 1/2 and 1/2 thats a Laguna body-1/2 Daves and 1/2 WSO. That stuff is bullet proof.They make it grog or sand and the sand has cracked some so I only use the groged on large press mold works.
Anything less than 12x12 I use straight Dave's on as well as all thrown production. I have used Dave's since middle 80's before Laguna Clay bought out Westwood Ceramics. Its only gone bad on me once in a major way and they never fested up but I did get my pound of flesh from the owner.
It was quite a story and I'm told they still recall it at the plant Jon Pacini later told me.