Concrete yard ornaments can add a sturdy yet whimsical element to your landscape. You can cast concrete ornaments for the yard using a variety of items to shape the mold. Large leaves from a banana tree or an elephant's ear plant make shapely molds for birdbaths, while wastebaskets and bowls can shape molds for concrete garden planters. Bottom line, if you can create the shape in a pile of damp sand, you can cast a concrete ornament for your yard.
Make a large pile of damp sand on a flat work table or on your driveway. You can use two sawhorses with a sheet of plywood on top as your work table. Make sure that you have easy access to all sides of the sand pile.
Shape the sand into a mound that is at least 3 inches taller than the height of the ornament mold. Sand casting will not pick up the intricacies of an ornament pattern, so concentrate on the shape of the ornament. For example, a metal star is a prime candidate for a sand casting mold, as the shape is very distinctive. If the star has carvings or embossed designs on the surface, chances are that the embellishments will not transfer well to the sand.
Push the ornament mold face down into the center of the damp sand mound. Do not press the ornament all the way to the table. Leave at least 2 inches of sand between the ornament and the table. Remove the ornament from the sand pile.
Sculpt the impression in the sand pile with your hands to smooth any cracks or to fill in any crevices where the sand loses its shape. The concrete will fill in any concave opening in the damp sand, so make sure that the impression looks like the shape of the ornament. Cover the impression with plastic wrap. Press the plastic wrap into the impression to conform to the ornament shape.
Spray the plastic with non-stick cooking spray. You can also use a commercially available concrete release agent.
Mix the concrete topping mix with water in a bucket according to the package directions. Topping mix is smooth, unlike other types of concrete mixes.
Fill the impression in the sand with concrete topping mix. Pour the mix directly on top of the plastic wrap. Tamp the mix as you pour it to fill in air pockets and to help keep it smooth. Pat the damp sand walls as needed to help hold the shape.
Leave the concrete in the sand to wet-cure for three to four days. Remove the concrete ornament from the sand and allow it to dry completely for up to one week.