How to make Rubber Molds for Casting

This is a description of how to make rubber molds for casting duplicates of the mold.

Things You'll Need

• Liquid Latex or Rubber Cement
• Paintbrush or paint spraygun
• Electric Hairdryer
• Cheesecloth
• Red rouge dry pigment
• Shallow box holding sand

Instructions

1. The idea of using rubber molds to make castings that are duplicates of naturally occurring objects dates back to at least the mid-19th Century. Rubber molds are usually used with Plaster of Paris although you can also use concrete for cast products for use outdoors. After the castings are made they are colored using acrylic paints that are water soluble. A casting made this way can be any size.

2. The mold itself is made from rubber mold latex that can be bought in most craft stores or in a store that sells model supplies. As an alternative to using rubber mold latex you can substitute rubber cement available at most stationary stores.

   In use you paint the rubber onto the object that you want to duplicate. Between each layer of rubber allow the rubber to dry thoroughly between layers. You can use an electric hair dryer to speed up the drying process. With the hair dryer this will take about three minutes. Without the use of the dryer allow at least an hour between layers.

   Some of the rubber compounds on the market are colored so you can see where you have painted. The rubber can be colored for this purpose by mixing some red rouge powder into it before you paint. As you paint the desired object be sure you work the first layer of rubber into all the nooks and crannies of the object.

   After you have applied six coats of rubber and allowed them to dry while the sixth coat is still tacky apply some cheese cloth over it and allow it to thoroughly dry. Apply two more layers of rubber over this and allow them to dry also.

   After all the layers have dried the mold is complete, and it is time to peel the mold from the object. In this process you have to be careful that you don't tear the mold, so peel it off carefully. The finished mold is now ready for use.

3. An alternate way of doing this is by embedding the desired objects in sand, and applying the rubber compound with a paint sprayer. To make this work you will have to thin the rubber compound so it passes through the spraygun freely. This process will also take more coats of rubber, but the advantage is you can coat several different objects at once making a master mold with several cavities.

   You will still have to use cheesecloth to make the molds stronger after you have sprayed several coats of rubber onto the objects you want to make molds out of. After molds are made this way they can be either cut apart or you can use the whole mold to cast several different moldings at the same time.

   Many people develop a part or full time business making these molds. You can make the finished product out of Plaster of Paris or concrete. You can make moldings out of wax that are used in jewelery making by the lost wax process. You can also use these molds for making wax masters that are used for making investment castings.

Tips & Warnings

• Set the object to be covered with rubber in a shallow box full of sand before applying the rubber compound.

• Liquid rubber compounds are highly flammable before they dry. Rubber cement was used as Napalm in the early days of WW II.