I was surfin on the net and found a few things on thin shelled cement My first hit, http://ns1.fidalgo.net/aqua/hcement.htm This one was way over my head. http://ciks.cbt.nist.gov/~garbocz/paper93/node5.html and my favorite: http://members.tripod.com/~V_Dodeja/wwf.htm Pat Mauk GA http://www.gnat.net/~goshawk "There is No Hope, but I may be wrong."