Silicone moulds or polyurethane moulds for concrete, stones and tiles?

Anyone casting concrete products such as decorative tiles, paving stones or ornamental elements quickly faces a choice between silicone moulds and flexible polyurethane moulds. Both materials work, but they perform very differently depending on the application, the production volume and the type of concrete mix. On this page we compare both options on the points that matter in practice, so you can make an informed choice before investing in mould material.

What is the difference between silicone and polyurethane moulds?

Silicone moulds are made from liquid two component silicone rubber, usually based on condensation or addition cure chemistry. They are extremely flexible, reproduce fine detail with great sharpness and release concrete without a release agent in most cases.

Flexible polyurethane moulds are cast from two component polyurethane rubber. They are tougher and more abrasion resistant than silicone at the same hardness, cheaper in raw material cost and better suited to rough, large scale production. The downside is that polyurethane is more sensitive to temperature, often requires a release agent and is less sharp on microdetails.

Detail reproduction and abrasion resistance in view

The two properties where these materials differ most. Silicone wins on detail, polyurethane wins on abrasion resistance under rough production.

Comparison by property

Flexibility

Silicone stays very flexible, even at low Shore A values. Polyurethane is also flexible, but at the same hardness it is generally stiffer than silicone. For moulds with deep undercuts or complex shapes, silicone therefore releases more easily.

Detail reproduction

Silicone copies fine textures almost perfectly and is the standard for decorative work with relief, wood grain or natural stone structure. Polyurethane performs well to very well, but becomes slightly less sharp on the very finest microdetails.

Releasing concrete

Silicone is naturally releasing and usually needs no release agent with concrete. With strongly alkaline or abrasive concrete mixes, a suitable release agent does extend the life of the mould. Polyurethane almost always requires a release agent to prevent sticking, which means extra work and a higher risk of air bubbles.

Abrasion resistance

Polyurethane is clearly more abrasion resistant and holds up better with coarse, abrasive concrete mixes and high production volumes. Silicone is more sensitive to wear with rough casting, but performs excellently in precise applications with fine mixes.

Chemical resistance

Polyurethane is more resistant to oils, plasticisers, pigments and cement water. Silicone is largely chemically neutral, although condensation silicones can soften with prolonged contact with certain solvents or plasticisers. Addition silicones are more stable in this respect.

Thermal stability

Silicone has excellent temperature resistance, typically from around minus 60 degrees to plus 200 degrees Celsius. Polyurethane is more limited and, depending on the type, often remains usable between 0 and 60 to 80 degrees. With heat accelerated curing or outdoor use in sun, this is an important consideration.

Service life and dimensional stability

Silicone is very dimensionally stable, shows no shrinkage and retains its dimensions even after many casts, provided the mix is not too abrasive. Polyurethane lasts longer with coarse masses and large series, but can deform over time, especially with incorrect storage or exposure to heat. Expect a slight shrinkage of about 1 to 2 percent during curing or ageing with polyurethane, while silicone shows virtually no shrinkage.

Repair

Polyurethane is more repairable with polyurethane bonding agents or hot air. Silicone bonds poorly to itself after curing, which makes repair difficult and replacement often the more practical route.

Price

Silicone is generally the more expensive option in raw material cost and polyurethane sits structurally lower. For large series with many casts, this difference weighs heavily. Check the current prices per product in our collection of silicones for concrete moulds and in the category flexible polyurethane rubber.

Advantages and disadvantages at a glance

When do you choose which material?

Recommended silicones for concrete moulds

For concrete applications we carry several silicones that prove their worth in practice. A short selection:

See the full range in our category silicones for concrete moulds.

Frequently asked questions

Do I need a release agent with silicone moulds for concrete?

In most cases no, because silicone is naturally releasing. With strongly alkaline or abrasive concrete mixes, a release agent is advisable to extend the life of the mould.

Which mould lasts longest in mass production?

With large series of rough or abrasive mixes, polyurethane generally lasts longer. For fine, decorative products in smaller volumes, silicone performs excellently.

Which mould gives the sharpest detail?

Silicone gives the sharpest detail reproduction and is therefore the standard for decorative work with fine relief or texture.

Can I use both materials outdoors?

Silicone tolerates sun and temperature changes better. Polyurethane is more sensitive to heat and UV and can deform with prolonged exposure.