Soft Shore A 20 condensation silicone for casting moulds. 100:5 mix ratio by weight, 20 min working time, 4–5 h cure. Ideal for resins, plaster and wax.
The EASYL 3520 is Feroca's reference condensation silicone: versatile, easy to mix and with a hard-to-beat quality-to-price ratio. At Shore A 20 it is soft enough to demould parts with complex undercuts and stable enough to withstand dozens of castings without losing definition. If you are looking for a general-purpose silicone for resins, plaster, wax or soap, this is the natural starting point.
The EASYL 3520 is designed to make flexible casting moulds for reproducing parts in different materials. Its Shore A 20 allows the mould to be bent and flexed without damaging it, making it ideal when the part has cavities, reliefs or difficult demoulding angles.
Moulds for casting plaster and gypsum (decoration, restoration, architectural pieces)
Moulds for polyester, polyurethane and epoxy resins
Moulds for fibreglass
Reproduction of wax pieces (candles, lost-wax casting)
Moulds for artisan soap (cold process and melt & pour)
Parts with undercuts and geometries that are difficult to extract
Series production of medium and short runs
Rotocasting with low-viscosity resins
How to use it
Prepare the original. Clean and dry the part to be moulded. If it is porous (plaster, wood, unglazed ceramic), apply a coat of Ferosil V 32 Release agent Paste or a suitable sealer to prevent the silicone from penetrating the pores.
Build the mould box. Surround the original with a watertight mould box (foam board, wood, 3D print) leaving at least 1–1.5 cm of silicone on all walls and the base.
Weigh the components. Use a precision scale. The ratio is 100 parts of Base A to 5 parts of EasyCat 3520 Catalyst by weight. Do not work by eye: an incorrect ratio produces an incomplete cure.
Mix carefully. Add the catalyst to the base and mix slowly and thoroughly for 2–3 minutes, scraping the walls and bottom of the container well. Avoid vigorous stirring to prevent introducing bubbles.
Degas if possible. If you have a vacuum chamber, degas the mixture for 1–2 minutes. Without a chamber, pour the silicone from a height in a thin stream so that bubbles can escape.
Cast over the original. Pour the mixture at the lowest point of the mould box and let it flow on its own towards the details. Do not pour directly onto the part to avoid trapping air.
Allow to cure. At 23 °C the demould time is 4–5 hours. Do not force demoulding early: even if the surface looks solid, the interior may still be soft.
Demould and clean. Remove the mould box, gently flex the mould and extract the original. Rinse the mould with water if necessary and let it rest for 24 hours before using it in production to ensure full cure.
Usage tips
Temperature and humidity
Condensation silicone cures by reacting with ambient moisture: an environment below 40 % relative humidity can slow down or hinder curing. Work preferably between 20 and 25 °C and at normal workshop humidity (50–70 % RH). If you need to speed things up, a slight increase in temperature (up to 40 °C) shortens the demould time without compromising the final properties.
Viscosity adjustment for skin moulds
If you want to apply the EASYL 3520 with a brush to make a skin mould or need a first layer that follows all the details without running, add Thixo Additive to the mixture to make it thixotropic. Another direct option is to use the EASYL Brushable Auto-thixotropic, formulated specifically for brush application. For the support jacket you can continue using the EASYL 3520 as a normal casting.
Pigmentation and run control
You can pigment the EASYL 3520 with pigments compatible with tin silicones. Do not exceed 3 % by weight of the total mixture to avoid altering the cure or the mechanical properties. Pigmenting each silicone casting with a different shade allows you to visually check how many layers the mould has and monitor wear from run to run.
Frequently asked questions
How many copies can a condensation silicone mould produce?
With correct use and appropriate release agents, an EASYL 3520 mould can yield between 30 and 40 copies under normal conditions. The determining factor is the material you cast: polyurethane resins are more aggressive than plaster or wax, so in those cases apply Ferosil V 32 before each casting to extend the life of the mould.
Do I need to use a release agent with silicone moulds?
It depends on the material. Plaster and wax usually demould without a release agent. With polyurethane or epoxy resins it is advisable to apply a thin coat of Ferosil V 32 before each casting: it reduces residual adhesion and noticeably extends the life of the mould.
Can I speed up the curing of the silicone?
Yes. Raising the ambient temperature to 35–40 °C (domestic oven, workshop heater) significantly shortens the demould time of the EASYL 3520. Do not increase the catalyst beyond the recommended ratio: excess catalyst does not accelerate curing linearly and can degrade the final mechanical properties or produce a sticky surface.
Is it compatible with epoxy and polyurethane resins?
Yes. The EASYL 3520 is compatible with epoxy, polyurethane and polyester resins. For freshly cured polyester resins, make sure they have completed their cure before using them as an original for the mould, as residual styrene can interfere. Always use a release agent to facilitate extraction and protect the mould.
Can it be used for moulding on skin or in food-safe applications?
No. The EASYL 3520 is an industrial-use condensation (tin) silicone. For Food Safe contact moulds you must use an FDA-grade platinum silicone (such as the Easyl 940-FDA). For skin moulds (lifecasting, prosthetics) a dermatological-grade platinum silicone is also required.
What happens if I mix the catalyst ratio incorrectly?
If you use less catalyst than indicated, the cure will be incomplete: the mould will be soft, sticky or with uncured areas. If you use too much, the cure may be superficially fast but the internal mass will be brittle with poorer mechanical properties. Always weigh with a scale and respect the 100:5 ratio by weight.
Can I use this silicone for rotocasting?
Yes. You can make the mould with EASYL 3520 and then pour rotocasting resin inside it. The silicone acts as a flexible mould and the low shrinkage (≤ 0.3 %) ensures faithful reproduction of the details in every cycle.
Can I add pigment to the silicone?
Yes, you can add pigments compatible with tin silicones. The maximum recommended proportion is 3 % by weight of the total catalysed mixture. Exceeding that amount can alter the cure time and reduce the mechanical strength of the mould.
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