Casting Compound

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Information about impression materials

In order to reproduce objects – for example, sculptures, models, surface textures or body parts – a mould must be made from the so-called “master pattern”. Elastic materials are the most suitable for making these moulds. We have assembled a list of them under the heading “Moulding materials” which can be found under the category “Modelling, Moulding, Casting”. They are:

• RTV 2 mould silicone rubber
• elastic polyurethane resin
• Latex milk
• Alginate

The following tables can provide you with an overview of the advantages and disadvantages of the various moulding materials.

Comparison of elastic moulding materials

Attributes Comp./Treatment

RTV 2 mould silicone

Elastic PUR resin

Latex milk

Number of components two two one one + water
Time and effort required very little very little very much very very little
Linear shrinkage very little very little very much very very little4)
  • reaction of 2 components
  • no heat produced
  • reaction of 2 components
  • heat produced
  • through drying

  • through “gelling”

Risk of inhibition yes no no no
Shelf life of the components (minimum) 6 to 12 months 12 months 24 months no information
Toxicological/hazard info as a rule, hazardous label NOT required2) as a rule, hazardous label required
hazardous label NOT required

hazardous label NOT required
Price high medium low low
Attributes when cured        
self-releasing yes no no no
Time before first use of the mould 1 day to 1 week approx. 4 days approx. 3 days approx. 20 minutes
Heat resistance high as a rule low low very low
UV resistance conditional low no no
Service life of the mould medium to long1) long short very short

Special features
  • can also be used as casting material

  • PUR components are sensitive to moisture
  • can also be used as casting material

  • smells like ammonia

  • mould must be kept wet
  • only good for a few pourings
Intended uses flexible and block moulds for all pouring materials flexible and block moulds for all pouring materials flexible moulds for non-aggressive pouring materials body casts without extensive quality demands

All the information refers primarily to the materials on offer at Modulor.
1) depending on the type of crosslink
2) Some hardeners require a hazardous label
3) at room temperature (annealing possible if applicable)
4) As long as pouring takes place within 20 minutes of making the mould

The listed materials can of course be used for other purposes – for example, silicone is used to make temperature resistant seals, elastic polyurethane to make foams and latex to make examination gloves.

Then again, hard, elastic materials like plaster are often used to make casts of objects. As a rule, very intricate moulds must be made for this work (see also the entry “Undercuts” in the “Small Lexicon” in the chapter “Silicone”).