While I am quite happy with the result, in retrospect, the amount of effort that went into making the mould just to cast one piece seems totally disproportionate and I wish I had taken the extra step (and cost!) and made a reusable mould in silicon rubber.
I am also slightly disappointed in the weight of the finished piece. One of my reasons for exploring mediums other than fired ceramic, is weight, clay being very heavy, it restricts the maximum size I feel happy handling. Even though this piece only has a concrete "skin", filled with expandable foam to reduce the weight, it is still very heavy! If I had made a reusable mould, I could have experimented with using lightweight materials such as the expandable foam alone.