I just threw a bag of the countertop mix in the car, along with 2 of the 45x90 pillars. Going to fill them at work tomorrow. Doing 2 at a time.
Side note. besides my X2 motor taking a dump, this was im sure a likely contributor:
DARN GIBS! One of the first things I plan to do when I finish my linear rail build, is to machine the gibs clear off my X2 build and convert that to linear rails.