Make a batch of stucco using one part Portland cement and two to five parts sand, depending on the how thick you want the stucco to be. The more sand you add, the less shrinkage you will get after the sculpture dries. Add water to the dry compounds. Mix the compounds thoroughly in a bucket.
Prepare the mold, ensuring it is clean on the inside. Join the pieces of the mold together and place the mold with the opening facing up, so you can pour the stucco.
Cast the stucco into the mold. Use small amounts of cement at a time. Prepare more stucco if needed. Fill the mold with stucco.
Allow the sculpture to dry in the mold. Cement contains various elements including silicates, which activate when water is added and harden in a few hours, depending on the size and thickness of your sculpture. Check if the cement has cured by introducing a finger in the opening of the mold.
Remove the mold to get your stucco statue. If the sculpture is large, ask someone to help you, so that the sculpture won't fall when you take the mold apart.
Sand the sculpture with a coarse-grit sandpaper. Check the sculpture at the joints of the mold --- these are the areas where you may have excess material that requires sanding.
Stain the sculpture and varnish it. Alternatively, add pigments to the cement mixture before casting it into the mold.