If you want to decorate your home, garden or patio with concrete sculptures or reliefs, you can choose from a variety of premade items at your local garden store. If you want your decor to be one-of-a-kind, though, you can create moulds to make your own concrete sculptures. Creating a concrete mould is not an easy process, but it can help you create decor that is uniquely your own.
Create your sculpture out of modelling clay, unless you plan to cast a found object. Relief sculptures, which are flat on one side, are much easier to cast than full-dimensional sculptures. If you choose a full-dimensional sculpture, use a section of thin wire tied to two dowel rods to cut it in half lengthwise. You will create two moulds, one for each half.
Coat the finished sculpture or found object with petroleum jelly. This will keep the object from sticking to the mould. Spread the petroleum jelly as thinly as possible so it does not alter the texture of your mould.
Fill a leakproof container with about 1 inch of pourable mould rubber. Place the sculpture in the container. Fill it with pourable mould rubber until it reaches the flat back of the sculpture or the centre cut, if you are casting a full dimensional sculpture. Let it sit overnight to allow the rubber to cure.
Pull the mould off of the clay sculpture or found object. Begin at one corner, gently bending the mould away from the cast object. Continue this process with the other corners of the mould, alternating corners until you have freed the mould.
Coat the mould with two thin layers of liquid latex before pouring concrete to cast your decorations. This will keep the concrete from adhering to the mould.
If you are casting a full-dimensional sculpture, insert a short dowel rod into the top of one of the halves of the clay sculpture. When you cast the concrete, you will put the two mould halves together. The dowel rod will create a hole you can use to pour in the concrete.
Always work in a well-ventilated area. Pourable mould rubber and liquid latex give off fumes that can irritate your eyes, nose and throat.