Casting ornamental concrete products can be a profitable addition to any precasting operation, but doing so with quality results and a minimum of work requires using methods that may be different than those used in creating other types of precast products. Because the goal in creating ornamental products is focused more on appearance than strength, the mix designs used in creating them differ from those used to create other precast products.
The mix should use a Type I portland cement, and good, clean water that is "fit to drink." Mortar sand is used by many ornamental casters because of its high quality surface finish. Use of gravel or crushed stone in ornamental concrete is optional. In order to produce a high-quality surface finish, the concrete should be mixed thoroughly. Calcium chloride can be used as an admixture to shorten set times and to place concrete at lower temperatures, and fly ash can be used as a substitute for a portion of the sand in order to gain a finer mixture.
To reduce weight when producing larger products, many precasters use empty containers or balloons to maintain a hollow space within the object. If the object is subject to easy breakage or freezing temperatures, it is wise to use some sort of reinforcement, such as wire mesh, small metal rods, or wire hangers in vulnerable areas.
Molds should be prepared with some kind of release agent, such as motor oil, silicone wax or paraffin and kerosene. There are three commonly used methods for filling molds: tamping, which uses a dry mixture that is placed in the mold and then packed into position; pouring, which uses a more watery mixture and creates a smoother surface finish; and vibrating, which uses mechanical equipment to vibrate the mold and speeds consolidation of the concrete.