Casting Compound

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	Alginate
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)
Curing	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
Comments
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”).