right so, thought i'd update this as i haven't in a while, i've found a few tricks that work with the chavant for me.
1. Microwave for about a minute and a half, slice about 10mm thick, cut some of these up to bars.
2. build a skeleton for the sculpt with the bars and use the slices as slabs to flesh out the sculpt.
3.melting a bit of chavant into a liquid state to use as glue for the slabs and bars saves a lot of effort.
4. microwave in pieces and get the general shape of the sculpt defined, oversized is best!
5 a household cheese grater shapes the sculpt quickly and easily but leaves ridges.
6. A washing up sponge, with the green abrasive side, dipped in white spirits will emulsify the top layer of the chavant and lest you scrub till it's smooth.
7. switching to the softer side and repeating will get it much smoother, and rubbing with a piece of paper towel will have it looking like a bowling ball.
that's where i'm at at the minute.... doing all the little touches and tricky bits. i've been taking pics all the way through it and i'll do a complete WIP post when i'm at the mold making stage!
thanks for all the pointers lads!