I used Celluclay for the first time on my my recent base and was most impressed.
I mixed in PVA (white woodworking) glue alongside Ceramcoat acrylic paints and spread it along the MDF base over a thin layer of PVA. Worked well and did not shrink in any discernable way.
Well worth the extra effort of buying the bag online as it is not available easily in my part of Australia.
cheers
Mike