Moldmaking introduction

Making your own molds is the next logical creative step in the manufacturing of garden stones. It takes your art to a new level that is not only more creative but very enjoyable. You can make a mold out of almost anything. In fact, because the material we will be using is flexible, you have much more flexibility in what you can cast. The molds you make can be pulled back at the edges to release your casting thus making it possible to cast items that have convex edges or undercuts. (like a garden bench) In addition, if you have ever considered getting into the statuary industry,learning to make the type of molds described in this guide is the first step.

A mold is used to create a replica of another object called the "model". This is done by imprinting a negative of the model into a material that can then be used to hold a casting medium like cement or plaster thus creating a duplicate of the original. Because it is relatively one dimensional, the process of creating a garden stone mold is actually quite easy.

This guide is specifically written as an instruction booklet for reproducing garden stones, stepping stones, wall plaques, and any other object that is relatively flat in nature. This type of mold is called a flat back mold. Although similar, the techniques described here are not applicable for molding more complex objects such as heads or sculptures. The process you will learn from this guide will create molds very similar to stepping stone molds. To use the new mold you simply pour, let it set, and pop out the duplicate.

Two types of garden stone molds will be demonstrated in this guide.

The first is a one pour method using a two part urethane molding compound. When poured greater than 1/2 inch thick this material requires no mother mold to support it while pouring castings. It is relatively simple to make but this type of mold is more expensive because of the volume of molding compound it uses.

The second type of mold is a brushed on mold with a mother mold to support it. A mother mold is a inexpensive second mold that holds the flexible mold in place while a casting is being poured. Urethane or Latex can be used with equal success. This method uses much less molding compound making it much cheaper to produce. However, because the molds are thinner and more flexible they require a mother mold made of plaster, fiberglass or cement to support them while castings are being made. Since plaster, fiberglass and cement are very inexpensive, the total cost of this type of mold is very low.

At the end of the guide there will be a listing of sources for the molding compounds that you will need along with the prices.

After you review this guide you should have a firm grasp on the following:

Choosing your model
Preparing your model
Sealing your model
Mounting the model to the baseboard
Building a containment frame
Sealing your containment frame
Applying a release agent
Mixing your liquid rubber or urethane
Pouring your mold
Making a mother mold when necessary
Demolding your model
Casting your first replica

-Your workshop should be at or near 70 - 80 Degrees. Warmer is fine but not colder. Good ventilation is an absolute necessity when using any molding compound. DO NOT INHALE FUMES of the rubber compounds, acrylic sealer or release agents.

-The workbench should be accessible from at least two sides and should have a hard level top. It should be protected against spills.

-Mixing containers and stirring paddles should be metal or plastic and always kept clean, warm and dry. Use 1-inch fiber brushes cut down to 1-inch length for application of wax release agent.

-A supply of paint brushs for brushing off dust and applying release agents. Also for applying molding compounds when using the brush on method.

-Clay is excellent for sealing models and dams and can be used for fixing imperfections in the model.

-Silicon caulk and a caulk gun are also useful for sealing the base of models and for sealing off the containment frame before pouring molding compound.

-Three eights plywood or a sheet of coreplast can be used for mounting models.

-Scrap pieces of plywood can be sawed to rectangular shapes and used for straight side retaining dams. Lightweight sheet metal, linoleum, heavy cardboard or coreplast which is a corrugated plastic used for signs can be used for circular or irregular shaped retaining walls. If you use corugated plastic you will need an exacto or utility knife to cut pieces for the containment wall.

-Sash cord, masking tape or hurricane tape can be used to bind the walls and attach them to the model baseboard.

-Spray acrylic is used to seal the model.

-A release agent to apply to the model and surrounding area prior to pouring the liquid rubber. A release agent can be made from mixing 10% castor oil and 90% alcohol.

-Liquid rubber or urethane molding compound. Available from www.cementex.com (zero-gel) or www.smoothon.com (pmc series) Molding compounds come in different shore hardnesses from 10 - 90 with 10 being the most flexible and 90 being the hardest. There are three basic kinds of molding compounds, latex, urethane and silicone.

• Liquid latex is taken from rubber trees and must be brushed on in layers to make a mold. It is very inexpensive ($25 per gallon). Since the molds it makes are soft and pliable a backup mold using plaster or cement must be used. If it is poured too thick it will not set up.

• Liquid Urethane comes in two parts and is mixed 50/50. It is more expensive and runs about $45 per gallon. It can be poured onto a model within a containment frame all at one time or brushed on to save material. If poured at least 1/2 inch thick a mother or backup mold is not needed. If brushed on a mother mold will be needed. It will set up no matter how thick it is poured.

• Liquid Silicone also comes in two parts. Its properties are similar to urethane but has the advantage of being more chemical resistant. It is by far the most expensive and runs about $100 per gallon. There are no examples of silicone in this guide but it would be used just as a urethane compound would.

The first method of moldmaking that is covered is the single pour method with no mother mold required. To make a mold like this you should use a two part urethane molding compound like the zero-gel from cementex.com or the PMC series from smoothon.com. They harden even when poured very thick. This method is the least time consuming but uses the most molding material.

The second method is the brush on method using a mother mold. This is the least expensive method of creating a mold because the molding compound whether it is urethane or latex based is brushed instead of poured onto the model in several coats thus using less material. Since the mold will be flimsy it is backed up with what is called a mother mold. The mother mold is made of a cheaper material such as plaster of paris or cement. A mother mold holds the latex or urethane mold in place while the cement or plaster is setting up.

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