General Steps to Sand Casting
As I remember, the very fine sand--almost like powdered "dirt" in consistency--was a barely moistened mix of sand and water with something added to the water to make it sticky. Then we'd add sand and pound it in place so when the upper mold was taken off the lower, the sand would not fall out [at least after a few tries]. Are you using dry sand or adding something to it to allow it to stick together in the mold? Source for your sand? Did you dust the mold and the separation area with talc or chalk to facilitate separating the mold halves? How did you remove the original model and leave the central sand core intact?
Sand casting is a process that uses a mold made from either metal, wood, or wax to create a negative impression in a special sand that will be the mold for the molten metal. This mold is then filled with a molten metal that is left to cool and solidify. Once the metal has solidified the mold can be hit with a hammer, pipe, or any hard object to crack the sand mold and expose the metal object.
The first step in making a sand casted object is deciding on the object. For this set of instructions I will be using a mug as my object. Once you have decided on the object you want to make you will need to figure out how you can cast said object and still be able to remove the sand mold from the form. This leads me to an important point about sand casting, because you need to be able to remove the sand mold from the form the complexity of the objects that can be molded is limited. It is also important to remember that you will need to leave a hole in the sand cast to pour the molten metal through when it is assembled.
1) Silica Sand
2) Mold of object
3) Some type of kiln/oven to melt the metal you will be using
4) Ladle to pour molten metal
5) Block of solid metal to melt
6) Hammer or some other object to crack the sand mold after metal solidifies