"N. Thornton" wrote in message
It shrinks and cracks during that time?

Unfortunately yes. A lot in summer, very little in winter. Only don't
expose it to frost or it cracks big-time.

I was reading up on making the stuff, and I gather quicklime is whats
wanted, slaking it yourself. I have some hydrated lime here - is it
possible to put it in the oven to dry it out? Or is that nuts?

Just throw a bag of hydrated lime in a clean plastic dustbin, fill with
water (use ALL the safety clothing you can get) and leave for a month,
stirring occasionally. Not quite as good as some of the best lime putties
but good enough.