Cement to fill speaker stands?

Use Caution padames, some cement mixes contain lime. If used in a metal stand you actually create a corrosive action, especially in high humidity conditions. In a wood stand the lime content will actally draw the natural oils from the wood and over a period of time will cause premature cracking, splitting, etc. Lime can be pretty nasty stuff.

BTW padames, if you visit a local diving/scuba shop, you'll find coated lead shot that is sometimes used for ballast bags. In most cases the shot is coated with a substance like copper or even a light wax to reduce toxicity. Usually more expensive than uncoated lead shot, but it will not reduce as many years from your life.
Cost is approx. 30% more than uncoated.