Methods on How to Make Concrete Molds

Bucket Mold

• Bucket molds are ideal when molding simple objects with flat bases such as pyramids and hemispheres. The object to be molded is placed into a cardboard box and brushed with a release agent such as petroleum jelly. Concrete is then poured into the box, filling it and covering the object by several inches. Once the concrete has dried, the cardboard is torn away and the object is removed from the mold. Box molds are very fast to make but are more expensive than brush-up molds because they use more concrete.

Brush-Up Mold

• A brush-up mold is used for objects similar to a bucket mold but requires less concrete. The object is prepared with a thin coat of petroleum jelly and must be sprayed with acrylic enamel spray (to seal the jelly) and dulling spray (to prevent concrete from beading on the surface). A thin coat of concrete, called the beauty coat, is brushed onto the object's surface to capture detail. After it has dried, a thick batch of concrete is spread onto the beauty coat to provide bulk and strength. Once the concrete has dried, the object is removed.

Two-Part Bucket Mold

• This type of mold is used for objects that need to be fully encased, such as a sphere. A line is drawn at the midpoint, and a shelf of modeling clay is built up against the lower side of the object until it meets the line. This clay forms the base for the first half of the mold. A box is constructed around the object, and a bucket mold is poured. When it is finished, the clay is removed and petroleum jelly is brushed onto the concrete. A second bucket mold is then poured on the other half of the object. Once it has dried, the two halves are separated.

Two-Part Brush-Up Mold

• A two-part brush-up mold is similar in preparation to a two-part bucket mold, where a dividing line is drawn and a clay shelf is built up. A brush-up mold is constructed on the first half of the object and once it has dried the clay is removed. Petroleum jelly is applied to the stone of the first half to prevent bonding, and a second brush-up mold is made.