A concrete bowl is made using a mold usually cut from Styrofoam or cast in rubber. For the do it yourselfer, the Styrofoam option is usually the best choice. There are several parts to the mold to form both the inner and outer concave edges. Once you make your mold you will be able to create several concrete bowls for use in your garden or as accents to your home.
Bowl Mold Shape and Size
A bowl mold is shaped to the size and contours of your bowl. When creating your mold you have the power to make any size and shape you like. The most common is a round bowl, but a square or oval bowl is also an option. To make a different bowl, simply cut the Styrofoam in a different shape.
Styrofoam is the most common bowl mold material and most accessible for the average bowl maker. However, other materials work just as well and can last longer. Styrofoam is available at some home and garden stores, hobby stores and direct from specialty manufacturers.
Molds are also made using a compound that is similar to rubber and considered a resin. This mold casting material is used when you have a particular bowl you would like to reproduce. The bowl is submerged into the compound and left to set. As it dries it hardens around the bowl, forming a reusable cast. Concrete or plaster is used in these types of molds.
Metal is another material used to create the molds. Copper, steel or brass are all used to build metal molds.You will need access to sheet metal and metal fabrication tools in order to use a metal mold, however. They will be more durable and may be used multiple times.
Cutting Styrofoam Molds
There are several ways to make a Styrofoam mold. You can cut the shape of the bowl in the Styrofoam using a carving knife. First, trace the outline of the bowl on the Styrofoam block using a pen and then cut into the block with the knife, carving out the area carefully. Another option is to use a jigsaw. This is an effective way to cut large bowl molds. Rotary tools with a sharp bit are also used to cut finer lines into the mold.
Creating the Mold Pieces
A bowl mold has two halves: one for the interior of the bowl and the second for the exterior. They fit like a sandwich on top of each other, leaving just enough space in between the two pieces to form the bowl. There are several ways to make these halves. One way is to carve both from Styrofoam blocks and assemble them together with packing tape when the cast is ready to be poured.
Another option is to use a metal bowl for one side of the mold. This is placed upside down in the bottom of the carved Styrofoam mold, or right side up with the concave area as the bottom half of the mold. In this case, the convex half of the mold is set on top of the bowl after the concrete is poured into it. The top half is secured in place with hand clamps or tape and left to dry.