got a lot of questions about how I make props, thus the video
Also known as "How To Use Cheap Hardware Supplies To Make Large Props (featuring: Expanding Insulating Foam)"
Part 2: http://youtu.be/hYibm69e8Fc
Updated to add, don't use the Great Stuff foam for this technique. It tends to shrink and expand a lot after being carved down (probably due to humidity). This means it won't hold its shape/surface well, and will eventually cause the plaster to crack.
written tutorial can be found here: http://commishenanigans.tumblr.com/post/72167578290/make-a-giant-club
for questions, or commissions, feel free to contact me @google.com (commishenanigans), or http://commishenanigans.tumblr.com/ask