Sand cast a concrete bird bath in the shape of a large elephant’s ear, gunnera, or banana leaf. To make concrete bird baths using leaf molds and the sand casting technique, you’ll need a pile of clean sand deep enough to make a concave impression with the leaf. Cover the depression in the sand pile with plastic wrap to reduce random grains of sand from contaminating the leaf mold and the concrete mix. Place the desired leaf in the sand depression, cover it with a release agent, and then spread the concrete mixture on top of the leaf, from the center outward. When the concrete dries, remove the leaf.
Two shallow bowls can also work as molds to make concrete bird baths. One bowl should fit inside the other, with a 1- to 2-inch space between the sides. Make sure to cover the inside of the largest bowl and the outside of the smallest bowl with a release agent. Spread the concrete mix inside the large bowl, and then press the smaller bowl on top of the concrete mix to shape the bird bath. Remove both molds after the concrete dries.
You can also sand cast a concrete bird bath using only one bowl. Make a cavity in the sand by depressing the bowl into the center of a sand pile. Remove the bowl, cover the depression with plastic wrap and pour in the concrete mix. Add a layer of a release agent to the outside of the bowl and press it into the concrete mix.
A terra-cotta saucer is another mold you can use to make a concrete bird bath. Use the sand casting method with one terra-cotta saucer, the same used with the shallow bowl. You can also press concrete mix between two different size terra-cotta saucers to make the birdbath.
Cardboard boxes, plastic milk containers, and large coffee cans are among the recyclable materials you can use to mold concrete bird baths. Many of these molds work best with the sand casting method, because you only need one item at a time to make the bird bath. Create a depression in the sand with the object, protect it with plastic, add a release agent, and pour the concrete. Control the depth of the bird bath by the thickness of the concrete layer.