Types Of RTV Mold Rubber


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.