Resin moulds provide endless opportunities to make customised crafts for fun or profit. Resin such as epoxy or polyester are liquids that set up into sturdy plastic pieces inside moulds of nearly any shape or size. You can use objects around your house to create moulds in urethane that can then be used for casting in resin. Urethane makes block moulds with only one pour, not requiring layering as with some of the other mould-making materials.
Attach your master part to an acrylic sheet using a glue gun. The master part is the piece you will be moulding the latex around for replication. Acrylic is nonporous, so it will not absorb any mould-making material. Gluing the master down keeps it from floating in the urethane.
Trim your vinyl sheets into 4-inch wide strips with your knife. These strips form the walls of the mould box that will closely conform to the shape of the master.
Bend the vinyl pieces around the master part, securing them to the acrylic sheet with a glue gun. Leave about a one-half inch of space between your master and the box's walls, so that you waste as little urethane as possible during pouring. The glue should make a tight seat around the bottom of the vinyl so that there are no leaks.
Spray the master part with mould release. Mold release is a lubricant that keeps the urethane from adhering to your master part and ensures a clean release when the urethane cures.
Fill the mould box with rice. Pour the rice from the mould into a measuring cup to find the volume of your mould.
Measure out equal amounts of urethane's side A and side B. Wear rubber gloves during the mixing process so that you do not get any urethane on your hands, as it is difficult to remove. Urethane comes in two parts that must be measured in equal amounts to form the urethane mould. If the volume of your mould box is one cup, then you will need a 1/2-cup of side A and an equal amount of side B. Mix the two parts thoroughly in a large plastic measuring cup using a wooden stir stick.
Pour the urethane into the mould box. Start pouring into one corner of the box, so that the urethane will push air bubbles out as it fills in around the master.
Release the mould from the master part. After 24 hours the urethane should be fully cured and release from the master easily.
Urethane produces no harmful fumes, so it can be mixed indoors without protective gear.