Silicone for concrete molds With silicone for concrete molds you make flexible molds for concrete, cement, cast stone, plaster and other mineral casting materials. Silicone releases by itself, reproduces the finest texture and stays flexible even after many casts. In this category you will find addition cure silicones for demanding...
Silicone to make molds for pouring concrete or cement (33)
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WackerWacker Catalyst T 37® – Hardener for ELASTOSIL® M Condensation Silicones & Mold Making
€5,95€4,92
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Silicone for concrete molds
With silicone for concrete molds you make flexible molds for concrete, cement, cast stone, plaster and other mineral casting materials. Silicone releases by itself, reproduces the finest texture and stays flexible even after many casts. In this category you will find addition cure silicones for demanding series production and condensation cure silicones for smaller runs and hobby projects.
Chemically, concrete puts a heavy load on a mold. The pH is around 12 to 13 and the mix is warm and moist while it cures. The silicone you choose therefore directly determines how many casts you get from a mold. Below you can read what to look out for.
What is silicone for concrete molds?
These are two component pourable silicones (RTV 2) that cure at room temperature into a strong, elastic mold. They are used for:
- ✓ Decorative concrete, garden ornaments and concrete decor
- ✓ Tiles, wall panels and brick slips with texture
- ✓ Cast stone, imitation natural stone and wood grain in concrete
- ✓ Architectural elements such as cornices, columns and facade parts
- ✓ Stamping mats and form liners for precast concrete
Why silicone?
- → Self releasing, with ordinary concrete a release agent is usually not needed
- → Perfect detail reproduction, down to the structure of wood or natural stone
- → No heat build up during curing, so no effect on your concrete
- → Stays flexible, so undercuts and deep reliefs demold easily
- → Good resistance to moisture, whereas polyurethane can foam at high humidity
Addition or condensation silicone for concrete?
The chemical difference
Addition cure silicones (platinum cure) crosslink without by products. They hardly shrink and stay dimensionally stable. Condensation cure silicones (tin cure) are cheaper and more forgiving to process, but shrink slightly and age faster.
Resistance to alkaline concrete
According to Wacker, addition cure silicones are more resistant to alkalis than condensation cure silicones. With strongly alkaline cast stone, condensation silicones can even cause white efflorescence on the surface. For series production, coloured concrete and large runs we therefore recommend addition cure silicones. Condensation silicones are fine for plaster, small series and hobby projects.
Mixing ratio and processing
Addition silicones are usually mixed 10:1 or 1:1 by weight, always weighed accurately. They are sensitive to inhibition by sulphur, tin and some clays or paints. If in doubt, do a small test on your model first. Condensation silicones are mixed with 2 to 5 percent hardener and are not sensitive to inhibition.
Why does a concrete mold wear out faster than expected?
With the right addition silicone you get hundreds of casts with ordinary concrete. If a mold already deteriorates after a few dozen casts, it is almost always due to one of these causes:
- → High pH combined with heat. Alkalis slowly attack the silicone surface. At higher curing temperatures this happens faster, research shows roughly a doubling at 40 °C compared to room temperature.
- → Alkali activated binders and geopolymers. Mortars based on blast furnace slag with water glass as activator are more aggressive than ordinary cement. A test with your own mix is always necessary here.
- → The wrong silicone. A silicone developed for prototyping or jewellery is not automatically suitable for concrete. Choose a type that the manufacturer recommends for concrete molds.
- → The wrong release agent. Mineral oil and petroleum jelly penetrate the silicone and make it swell, so the surface wears faster and concrete starts to stick.
⚠️ Polyurethane with strongly alkaline mortars: polyurethane is more wear resistant than silicone, but sensitive to strong alkali and water glass. Polyester polyurethane degrades fastest, polyether polyurethane holds up better. If you work with geopolymers or alkali activated mortars, always test first.
Our silicones for concrete molds
Addition cure silicones for series production
Wacker Elastosil M 4630
Shore A 28, low viscosity. Recommended by Wacker for concrete molds, ideal for fine textures.
Shore A 28, low viscosity. Recommended by Wacker for concrete molds, ideal for fine textures.
Wacker Elastosil M 4601
Shore A 28, high tear strength. Strong all rounder for molds that see heavy use.
Shore A 28, high tear strength. Strong all rounder for molds that see heavy use.
Polytek PlatSil HTS 40
Shore A 40, very high tear strength and elongation. Made for demanding production environments. The softer HTS 25 is also available.
Shore A 40, very high tear strength and elongation. Made for demanding production environments. The softer HTS 25 is also available.
Siliconen Additie Kleurloos 50
Hard mold for heavy casting materials. Can be mixed with Kleurloos 25 for any hardness in between.
Hard mold for heavy casting materials. Can be mixed with Kleurloos 25 for any hardness in between.
Wacker Cenusil M 825
Pourable addition silicone for concrete and reproduction molds, economical in larger packs.
Pourable addition silicone for concrete and reproduction molds, economical in larger packs.
CHT QM 270
Shore A 62, for hard, dimensionally stable molds in architecture and the furniture industry.
Shore A 62, for hard, dimensionally stable molds in architecture and the furniture industry.
Condensation cure silicones for small series and hobby
Siliconen Condensatie 35
Medium hard, suitable for concrete and plaster molds.
Medium hard, suitable for concrete and plaster molds.
Siliconen Condensatie 20 Universeel
Affordable all rounder for decorative concrete, plaster and candles.
Affordable all rounder for decorative concrete, plaster and candles.
Wacker Elastosil M 4514
Pourable condensation silicone from Wacker for reproduction molds.
Pourable condensation silicone from Wacker for reproduction molds.
Dow Silastic RTV 3481 R
Condensation silicone for resin and concrete molds.
Condensation silicone for resin and concrete molds.
Read more: free background information
📄 PDF download · Wacker brochure
Moldmaking for concrete and cast stone
Silicone or polyurethane for concrete, stones and tiles?
Make your own silicone mold of decorative concrete
Moldmaking for concrete and cast stone
- ✓ Which ELASTOSIL M silicones Wacker recommends for concrete molds
- ✓ Silicone versus polyurethane for wet cast concrete
- ✓ Applications such as cast stone, facade elements and stamping mats
Silicone or polyurethane for concrete, stones and tiles?
- ✓ When silicone is the better choice
- ✓ When polyurethane works out cheaper
- ✓ Pros and cons for wet cast production at a glance
Make your own silicone mold of decorative concrete
- ✓ From model to ready to use mold
- ✓ How much silicone you need
Tips for a long life of your concrete mold
- ✓ Let the mold cure fully before first use. A short post cure at 60 to 80 °C makes addition silicones extra stable.
- ✓ Preferably use no release agent with ordinary concrete. If you do need one, use a thin mist of the Achem BL-3007S or Achem SG-1008S release spray, which in our experience work well with silicone. Avoid mineral oil and petroleum jelly on silicone.
- ✓ Keep the curing temperature of your concrete as low as your process allows. Every degree warmer speeds up the ageing of the mold.
- ✓ Clean the mold after every cast with water and a soft brush. For oil and grease residues use Kirasol 318 SC, a mild water based cleaner.
- ✓ Store molds flat, dry and dark, with no weight on them, so they do not deform.
- ✓ Large series? A solid silicone mold is not always the smartest or most economical solution. We are happy to think along with you about other, smart solutions that better suit your production and volumes.
Frequently asked questions
How many casts do I get from a silicone concrete mold?
With addition silicone and ordinary concrete, Wacker states 100 to 1000 casts. The actual number depends on your concrete mix, the curing temperature, the shape of the mold and how you demold.
Do I need a release agent?
With silicone and ordinary concrete, usually not. With aggressive or very fine mixes, a thin layer of release spray can help, for example Achem BL-3007S or SG-1008S. Always test this on a sample first.
Which hardness should I choose?
Shore A 20 to 30 for molds with lots of relief and undercuts. Shore A 40 to 60 for flat products such as tiles and slips, where dimensional stability matters more than flexibility.
Can I use silicone for geopolymer or alkali activated mortar?
Yes, but these mortars are more aggressive than ordinary concrete. Choose addition silicone and test with your own mix and curing temperature before making a series of molds. We are happy to help you set up a test.
Can you make the mold for me?
Yes. Via request a custom mold we make molds based on your model or 3D file, from a single prototype to series production.
Related information
Not sure which silicone suits your concrete?
Tell us which mix you cast, how warm it cures and how many casts you need. We will advise you on the right type, the hardness and a release agent if needed. Email info@siliconesandmore.com.
All information is based on experience and manufacturer information, but offers no guarantees. Customers are responsible for testing suitability for their own application.