Poly 74-30 is a Shore A30 casting polyurethane rubber designed for the production of high-output flexible moulds. Its equal-parts mix ratio, long working time and excellent compatibility with concrete and cement make it a solid reference for architectural reproduction, sculpture and ornamentation workshops.
Technical specifications
| Parameter |
Value |
| Application |
Casting |
| Mix ratio (by weight) |
100A : 100B (1:1) |
| Shore Hardness |
A30 |
| Working time |
25-30 minutes |
| Cure time (demould) |
16 hours |
| Colour |
Amber |
What it is used for
Poly 74-30 is formulated for the production of flexible moulds that require a soft, tear-resistant rubber. Thanks to its excellent behaviour with pigmented concrete, the resulting castings show precise and uniform colours without the mould absorbing or altering the pigment. It is a common choice in the following fields:
- Casting of concrete and decorative or architectural cement
- Reproduction and restoration of architectural elements (mouldings, bas-reliefs, capitals)
- Decorative woodwork and ornamentation
- Sculpture and artistic casting
- Production of candles with complex geometry
- Reproduction of plaster or wax pieces
- Theming and set design
- Prototypes and medium-run industrial applications
How to use it
- Prepare the original surface. Clean the model and apply a suitable release agent if the material to be cast requires it. Plaster and wax usually release without a release agent; concrete and polyurethane resins always require one.
- Weigh the components. Mix Part A and Part B in a 100:100 ratio by weight. Use a scale to achieve reproducible results.
- Mix carefully. Stir slowly and evenly for 2-3 minutes, scraping the sides and bottom of the container thoroughly to fully combine both components without incorporating excess air bubbles.
- Pour over the model. Pour the rubber in a thin, continuous stream from the lowest point of the mould so that the material flows on its own and displaces the air. Working time is 25-30 minutes.
- Allow to cure. Keep the assembly at room temperature (ideally between 20-25 °C) without moving it for the 16-hour cure time.
- Demould carefully. Once the cure time has elapsed, demould gently. The mould will be ready for its first use.
Important notice — Polyurethane rubbers: Polyurethane rubbers are moisture-sensitive. Always store components with containers tightly sealed and work in an environment with the lowest possible relative humidity. Contact with water or excessive moisture can generate internal bubbles in the cured rubber and deteriorate its mechanical properties. Maximum operating temperature of the resulting mould: do not exceed 60 °C.
Usage tips
Temperature and working environment
Ambient temperature directly affects working time and cure. Below 18 °C the process slows down significantly and the result may be an incomplete cure. Above 30 °C the working time shortens and may be insufficient for large castings. The ideal range is 20 to 25 °C. If the workshop is cold, slightly pre-warm the components (no more than 30-35 °C) before mixing.
Release agents and material compatibility
For concrete or cement castings, always apply a suitable release agent to the inside of the mould before each use. Without a release agent, the alkalinity of cement can attack the rubber and reduce the mould's service life. For castings of rigid polyurethane resins such as Feropur PR55+E55, a release agent is equally essential. With plaster and wax, a light release agent or even none is usually sufficient, but always run a test with the first piece.
Pigmentation of the cast material
One of the advantages of Poly 74-30 is that it does not interfere with concrete pigments. If you are casting coloured cement or plaster, the tones of the casting will be faithful to the original. If you need to colour the rubber mix itself, use paste pigments compatible with polyurethanes: Feroca's range of paste pigments is compatible with all polyurethane rubbers and resins in the catalogue. Add the pigment to Part A before mixing with Part B, and homogenise thoroughly before combining both components.
Frequently asked questions
Is it necessary to use a vacuum chamber to degas?
No. Poly 74-30 is formulated so that vacuum degassing is not required. Its viscosity and formulation allow bubbles to escape naturally during casting if you pour the material in a thin stream without vigorous agitation. If you want an optimal result on very fine detail pieces, you can use vacuum, but it is not essential.
Do I need a release agent to cast concrete or cement?
Yes. For castings of concrete, cement or polyurethane resins it is always necessary to apply a suitable release agent to the inside of the mould before each casting. The alkalinity of cement can damage the rubber over time if it is not protected. Plaster and wax are materials that usually release without a release agent, although it is advisable to run a test with the first piece.
How many castings can a mould made with this rubber withstand?
Poly 74 series moulds have a high production life. The exact number of castings depends on the cast material, the use of a release agent and the care taken during demoulding. With concrete and a correctly applied release agent, it is common to obtain tens or even hundreds of reproductions with no appreciable loss of detail.
What is the maximum temperature at which the mould can be used?
Polyurethane rubber moulds must not exceed 60 °C. Above this temperature the material may deform and lose its mechanical properties. If your process requires higher temperatures, consider alternative materials such as high-temperature silicones.
Can colour be added to the rubber before curing?
Yes. You can incorporate paste pigments compatible with polyurethanes directly into Part A before mixing with Part B. Feroca's range of paste pigments is fully compatible with this rubber. Mix the pigment thoroughly into Part A until a uniform colour is achieved before combining both components.
Can this rubber be used to make silent blocks or technical parts subject to vibration?
For technical applications such as silent blocks or anti-vibration mounts, higher-hardness polyurethane rubbers are recommended. Poly 74-30, at Shore A30, is too soft for these applications. Contact Feroca to find out which hardness best suits your specific case.
Is it possible to reinforce the mould with fibreglass or carbon fabric?
It is not recommended. Reinforcement fabrics such as fibreglass or carbon are designed to work with rigid materials. In a flexible rubber like Poly 74-30, the fabric does not integrate correctly and can create stress points that deteriorate the mould. To gain consistency in large or complex moulds, the usual approach is to make a rigid outer shell (mother mould) with high-strength gypsum or resin.
Can I use silicone oil to reduce viscosity?
No. Silicone oils are additives designed specifically for silicones and are not compatible with polyurethane rubbers. Adding silicone oil to Poly 74-30 can interfere with the cure and degrade the mechanical properties of the resulting mould. If you need to adjust viscosity, consult Feroca for additives compatible with polyurethanes.
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