For working with our cast products, we describe the most commonly used casting materials and pour methods for making molds.

Materials & methods

To help you with the first use of new materials, the following instructions and recommendations provide the best chance of success:

• Always read the product information such as TDS (Technical Data Sheet), label and other literature on how the materials should be processed.
• Do not deviate from the prescribed method and techniques, never use other release agents than prescribed!
• First make a small mold or casting, before an attempt is made to make a larger mold or casting. Small objects or a small piece can serve as a test model.
• First make a small amount. Try to develop a feel for the materials before making costly and time-consuming mistakes while working on a larger object.
• Do not hesitate to ask questions before you start your project. We will try to answer all your questions about molds and models. If you are not sure, ask more information first or contact our customer service!

Schouten SynTec® have all kinds of flexible mold materials – for both industrial, medical, private and commercial use, such as polyurethane, silicone, resins, gypsum, concrete and alginate products. SynTec products usually consist of two components. The components vulcanize, cures, at room temperature (RTV: Room Temperature Vulcanization).

Polyurethane rubber or resin is a relatively inexpensive material. Silicones (on an additive basis) are slightly more expensive, often twice the price of most cheap silicone in the market (Condensation silicone, our SG C-sil) or polyurethane rubber. Gypsum / concrete is the cheapest and is therefore often used as a material. Gypsum and concrete (concrete, gypsum mortar and gypsum powder) are available in many formulas for various purposes. See our extensive plaster information. Polyurethane resins are also pourable, but the use of this material is limited by the stiffness and shrinkage upon curing of this material.

Metal alloys with a low melting point can be cast in a heat-resistant silicone rubber. Epoxy resins and polyurethanes, the two most used two-component synthetic resin systems, offer great applicability.

Polyester synthetic resin is a two components molding resin and relatively inexpensive. Especially if sand, limestone or wood pulp are added as filler. Big disadvantage is that polyester, styrene contains, this is a carcinogen. There are already styrene-poor polyesters on the market.

Synthetic resins have the disadvantage of rapid flammability, a strong odor (in liquid form) and a shrinkage (especially with large objects) during the curing time. After reading some literature and performing some experiments, you learn to recognize the differences and the advantages and disadvantages of the various materials.

Making the mold and the type of casting method

Make sure that each mold and casting compound is unique and that this requires a tailored treatment of the materials, which may differ from other materials that you have previously worked with. Pay attention and time to a good preparation. First make a small test of the materials you will be working with before the material is used on a large scale. With this method you avoid unnecessary time and loss of materials.

Molds are generally made of liquid casting rubber. The casting rubber is poured over the model that is surrounded by a box or support mold. Another method is to brush with a brush or spatula of thick rubber on the model. The mold shell ensures that the entire mold remains in shape until the rubber has cured.

Molds (pour)

The most flexible times are casting molds. The easiest way to produce a mold is to build a box around a model so that the casting material can be poured into it and then harden into a hard and solid rubber mold.

Complex molds can be made in parts. Each part is then poured separately. When all parts have been poured and hardened separately, the model is taken out and the mold parts reassembled.

Brush molds

Most rubber types can be thickened so that a brush mold can be made. The thickened rubber can be applied to the model with a brush or spatula. A liquid rubber is not suitable for this because the rubber flows away from the vertical surface. This mold is then built up in layers. By adding the Eurosil thickener almost any silicone can be used to make a brush mold. The silicone gets a higher viscosity due to this additive.

Some products, such as latex, are only suitable for brush molds. brus molds are generally faster to produce and provide the user with a better visual inspection of the rubber being applied. Another advantage is that when making a brus mold, less material is needed than when casting the mold. With a brus mold, a support mold / mold shell must be made always (from, for example, plaster, polyester or resin).

You must be careful that the original model does not get stuck to the undercuts of the support template. All undercuts must be removed unless the mold shell consists of several parts. Flexible support jigs often offer a good solution with regard to the undercuts mentioned. Filler pieces are used to create seams and dividing lines if required. Usually it takes more time to make a syrup mold because of the layer of build-up, drying time and the amount of work.

Castings – cast into the mold

When the mold is ready and you are going to pour a model, it is important that the mold and the mold shell are positioned level. This prevents mold from flowing out of the mold and being lost. The mold is filled to the top with cast material. If there are too many air bubbles in the casting material, you can vibrate the mold slightly, it is of course better to ensure that you mix the casting well without air bubbles. Then just let it cured.

Air bubbles in the casting material can be prevented by mixing the molding material under vacuum or by mixing and possibly pouring under vacuum. We do recommend this.

It is important that the castings are removed from the mold in time, always follow the instructions in the technical data sheet (TDS). Never demold it too quickly, but certainly not leave the castings in the mold for several days. In this way, detailed castings of high quality can be manufactured.

Use release agent or a sealer if necessary. Consult our sealer and release menucard for the resources about the agents.

What can go wrong?

Below we have described a number of problems that can arise when creating a mold and model.

Wrong mixing ratio

Material that does not harden at all, remains soft or sticky, is often the result of a wrong mixing ratio. We always recommend carefully weighing the materials before use. Carry out correct calculations and build a double check with regard to the mixing ratio as described on the labels and the data sheets.

Release agents

Before you start, consult whether you should use release agent or which release agent you must use. Do not use a release agent if this is not necessary. Pay particular attention to the mutual material combinations. For example: PU (polyurethane) adheres to polyurethane. Never use too much release agent, this can lead to a porous and greasy surface of your casting.

Temperature and demoulding

Large temperature differences and the rapid deformation can be the cause of deformations of the mold or cast model. At too low a temperature (below 10°C) the processing time and the curing time are drastically delayed. Because of this, it takes much longer before you can demold the mold and model. The viscosity can also increase with this lower temperature.

If the temperature is too high (above 30°C), the processing time and the curing time are accelerated. This can be an advantage if you want to work quickly. General advice: maintains an operating temperature of 20° C to 25° C! Temperature fluctuations can lead to air bubbles and dimensional changes. The viscosity can also decrease.

Leaking molds

Molds can be lost through a leaky mold, time is wasted and the mold usually fails. Always check in advance if a leak can occur. Close corners and seams well with, for example, a dry clay or sealant. PAY ATTENTION!

Never use a “wet” clay (river clay) in combination with Polyurethane or Silicone on an Additive basis. The moisture in the clay disturbs the hardening of the rubber, the rubber remains soft and sticky and hard not completely. Use Plasteline synthetic clay for this! Only with Silicones on a condensation basis you can use a “wet” clay. Clamps and straps can also prevent leaks.

Speed

Avoid delays because there is no good preparation after two components are mixed together. It is advisable to keep the clock..

Unmixed material

Strips of uncured material or air bubbles, which can be seen on the surface after hardening of the rubber, may be the result of insufficient mixing of components A and B.

Unmixed rubber is often on the side and on the bottom of the mixing cup during mixing. Mix the components carefully and carefully. Slightly scrape along the edges and over the bottom of the mixing bowl with a spatula. Do not pour everything into the mold or mold formwork. The edges and bottom can best be considered as “waste”.

Shake / stir before use

Some components of polyurethane or silicone must be shaken or well stirred before use. Sludge can sit in the packaging, and the oils often float so always check and shake or stir! This is always indicated on the packaging.

Unmixed material can result in insufficient or total no cure. Air bubbles and weak spots can also arise in the mold.

10 rules for making a mold / model

1. Always read the label, the processing sheet and the safety data sheet before use!
2. Choose the right material for your work, ask our advisers for it!
3. Wear gloves and, if necessary, a suitable mouth mask, safety goggles and any additional protection!
4. Provide clean and good tools!
5. Work with materials that are already at room temperature in a room at room temperature!
6. Shake or stir components thoroughly before use!
7. Weigh all components well, always keep the right mixing ratio, stir well and do not pour unrestrained parts!
8. Avoids pouring delays
9. Before pouring, check your mold to prevent leakage and if any necessary release agent and sealers are used.
10. Maintain the indicated deformation time to prevent deformations.

Overview of common rubbers, pour materials and the processing / pouring methods.

Rubber types

rubber (DPR)	Benefits	Disadvantages	Used for	Processing method
Polyurethane casting rubber	•     Relatively low costs •     very strong •     many applications •     shrinkage nil	•     release agent needed •    Moisture sensitive •     Two Comp.	•     plaster •     concrete •     Cement •     Wax	•     Casting •     brush on
C-Silicone  Condensation / tin cured	•     No release agent needed •   affordable •     Very strong •     many applications	•    More expensive than PU (polyurethane) •   1% shrinkage max. during curing. •     Two Comp.	•     Gypsum •     PU resin •     Polyester •     Wax •     Expoxy •     alloys with low melting point	•     casting •     Brush on
Silicone Addition / Platinum cured	•     No release agent needed •     Shrinkage nil •     Very Strong •    durable	•    More expensive than silicone condensation •    sensitive to dirt and moisture	•     Plaster •     concrete /Cement •     PU resin •     Polyester •     Wax/Epoxy •     acryl resins •    alloys with low melting point	•     casting •     Brush on

Casting materials

The most used casting materials from Syntecshop

 

	Benefits	Disadvantages	Applications
Plaster	•     Goedkoop •     Éénvoudige verwerking •     Niet giftig •     Veelzijdig inzetbaar •     Snelle uitharding •     Overschilderbaar en in te kleuren	•     Breekbaar •     Alleen voor binnen	•     Beelden •     Ornamenten •     Reliëfs •     Kunst objecten •     Holle beelden
Concrete	•     Sterk •     Goedkoop •     Geschikt voor buiten •     Éénvoudig verwerking	•     Zwaar •     Ruw oppervlak •     Alleen om te gieten	•     Buitenbeelden •     Balustrades •     Beton industrie •     Architectuur
Polyurethane resins	•     Sterk •     Éénvoudige verwerking •     Snelle uitharding •     Veelzijdig inzetbaar •     Mengbaar met metaal- poeders •     In te kleuren	•     Niet goedkoop •     Brandbaar •     Geur •     Zonder voorbehande- ling niet overschilder- baar •     Gevoelig voor vocht	•     Kunst objecten •     Ornamenten •     Reliëfs •     Holle modellen •     Metal look mogelijk
Epoxy resin	•     Zéér sterk •     Lange levensduur •     Hittebestendig	•     Duur •     Moeilijk te mengen •     Gevoelig voor vocht	•     Modellen voor vacuüm- vormen •     Diverse toepassingen
Polyester resin	•     Goedkoop •     Snelle uitharding •     Sterk •     Te gebruiken in combina- tie met glasmat	•     Bevat styreen •     Sterke geur •     Niet UV bestendig •     Hoge krimp	•     Veel toepassingen o.a. kunst objecten, repara- tie voor b.v. boten etc.

Methods

Most used methods for making rubber molds

Technic	Benefit	Disadvantages	Applications
Casting	Éénvoudig Snel	Volume Gewicht	Mallen Modellen Beelden etc….
Brush on	Éénvoudig Materiaal besparend Geschikt voor moeilijke objecten	Kost meer tijd dan gieten Steunkap nodig Laag op laag vraagt meer aandacht	Stroopmallen
Dipping (Latex)	Goedkoop Simpel Sterk	Kost veel tijd door laag op laag Krimp 10%	Stroopmallen Condooms, Ballonnen, schoenindustrie etc…
Hollow casting rotational molding Plaster and resins	Snel & Licht Gemakkelijk Geschikt voor moeilijke objecten Kan opgeschuimd worden	Machine nodig Breekbaar	Holle modellen Kunstobjecten Gipszuilen Etc…
Injection resins	Hoge kwaliteit Sterk Maatvast	Kost veel tijd Machine nodig Kennis en ervaring gewenst	Technische modellen en onderdelen
Vacuum en pressure casting	Hoge kwaliteit Géén luchtinsluiting Maatvast	Kost veel tijd Machine nodig Kennis en ervaring gewenst	Prototypes Figuren/beelden Technische modellen en onderdelen