Overview
Examining the different types of RTV mold rubber available for mold making and casting as well as each materials strengths and weaknesses.
Advantages of Latex:
- Least expensive mold rubber available.
- Very elastic, thin-walled and strong.
- Lasts a long time.
- Offers good abrasion resistance.
- Good for making glove molds.
Disadvantages of Latex:
- Strong ammonia smell.
- Can only be brushed onto an original.
- Many coats are necessary.
- Can take up to two weeks to make mold.
- Shrinkage.
Casting with Latex:
- Good for casting concrete, wax or plaster.
- Generally not used for casting urethane, polyester, or epoxy resins, or low-temp metal alloys.
Advantages of Polysulfide:
- Soft, stretchy, and durable.
- Last a very long time.
- Moderate cost.
- Will cure against water clay or clays containing sulfur.
Disadvantages of Polysulfide:
- Accurate gram scale to weigh components.
- Offensive odor.
- May stain white plaster during casting.
Casting with Polysulfide:
- Good for casting plaster or wax only.
- Will not handle concrete, resins, or low-temp metal alloys.
Advantages of Silicone Rubber:
- Best release properties of all the mold rubbers.
- Model surface preparation minimal nor not necessary.
- Release agent for casting often not necessary.
- Most heat resistance to high temperatures.
- Can cast low-tempmetal alloys such as tin and pewter.
- High tear resistance.
- Knotty tear propagation.
- Very good chemical resistance.
- Longest mold life for casting urethane, polyester, or epoxy resins.
Disadvantages of Silicone Rubber:
- Price.
- Require precise measurement.
- Air entrapment. Vacuum degassing may be necessary.
Disadvantages of Tin-Cure Silicone:
- Will shrink somewhat over time.
- Will lose tear strength when stored in library over time.
Disadvantages of Platinum-Cure Silicone:
- Most expensive available.
- Cure inhibition.
Casting with Silicone:
- Appropriate for most casting materials.
Advantages of Polyurethane Rubber:
- Available in a wide hardness range.
- Last a very long time.
- Cost less than silicones and polysulfides.
- Accurate gram scale often not required.
- Vacuum degassing generally not required.
Disadvantages of Polyurethane Rubber:
- Sticks to most surfaces.
- Model preparation generally required before pouring.
- Release agent may be necessary before casting.
- Moisture sensitive.
- Very limited shelf life after opening.
Casting with Polyurethane:
- Good for casting wax, plaster, concrete and resins.
- Will not handle the heat of low-temp metal alloys.