How To Make a Latex Rubber Mold
Liquid latex rubber is a very popular mold making material as it can be used to cast various materials like plaster, polyester resin, urethane and so on. The molds are so tough and tear-resistant that they can withstand abrasive materials like cement and concrete too.
The liquid latex itself can serve as an adhesive for the base. When dry, Latex is applied to your model by painting it on. To achieve the correct thickness, you will require twelve to fourteen coats. Each coat must be dried before the next coat is dried. If it is not dried, when you apply the next coat. It will never dray, once covered. Use a brush and carefully work it into the undercuts so that the mold captures all the details properly.
The latex rubber layer requires about three hours to adequately dry. But, the process can be speeded up with a fan. Once you achieve a thickness of about 1/8th of inch (12-14 layers). You are complete with the flexible part of the mold.
After about the tenth layer, it should be reinforced with cheesecloth to improve its life and performance. Apply a coat of latex rubber as earlier before embedding strips of cheesecloth in an overlapping manner all over the mold. This is topped off by another coat of latex rubber.
Once this layer is dry, a couple more coats are applied as usual. After the latex is dry, plaster must be applied to form a ridged mother mold to support the flexible rubber mold. Plaster is applied to a thickness of two to three inches. After the plaster sets, the plaster and latex mold is ready and can be demolded and used for making the casting.
Fiberglass or even plaster can be used for the support shell. Mold release is applied all over the latex mold before laying down strips of fiberglass to cover the mold. A polyester resin should be mixed with the fiberglass hardener and poured over the fiberglass cover.
When this is semi-dry, two more layers of fiberglass matting and resin mix are consecutively applied on the mold. Allow this support shell to dry completely before demolding them and finishing them properly. Both the latex mold and shell mold will come off easily and can be used together for making castings of choice.
Now that you know how to make a mold for say, concrete castings, you can use it easily to pour concrete and make blocks or other items straightaway. The mold can be used again and again to make as many casts as you wish.