CS25 Condensation Cure Silicone Rubber

For metal casting at home, most people tend to use special 'low melting point' metal alloys, rather than regular lead. The reason for this is that regular lead has a melting point of 327°C which is too high for any type of moulding silicone rubber. Special 'casting alloys' tend to be a tin/antimony/lead alloy and have a melting point around 190°C and a recommended pouring tempertaure of around 240°C which is much more suitable for casting into silicones, which tend to have maximum service temperatures of around 250°C, including both our CS25 and AS40 silicones.

In terms of a recommended silicone, both CS25 and our AS40 can be used as moulds for metal casting if you're using a casting alloy that can be cast at 250°C or less. If you were using regular tin then I'd steer clear of silicones altogether, none of them can reliably be used for the 350°C pouring tempertaures you would need for lead. Out of the two, CS25 is lower cost and easier to use but it will deteriorate faster than AS40 so it would be the best option for smaller numbers (say less than 20) but if you want to make large quantities of the castings then AS40 would be better.

Metal won't stick to silicone so you wouldn't need any sort of release agent or any other products in order to start casting pieces like small soldiers using a low-melt casting alloy.

No, we do not have any additives that will reduce the viscosity. However, often despite the apparent high viscosity, the Silicones have very good flow properties and will flow into fine details and gaps much smaller than you would expect.

Generally speaking, no, you do not need a release agent as really doesn’t stick to much at all. There are a couple of exceptions; firstly it sticks very well to itself and secondly it can stick (or at least ‘grip’) to porous materials. Porous materials and items with fragile surfaces should be sealed to prevent any sticking or damage during the moulding process. PVA, Shellac (sanding sealer) or paint/lacquer can all be used to seal the surface of porous materials. If in doubt, always test a small area first.

As long as the surface is free of dirt and contamination, then this silicone will stick to itself when you do the second pour. If the first pour of silicone has fully cured when you make the second pour then although it will bond and will become a single piece mould, the bond-line is likely to remain a weak-point.

The silicone itself can certainly be used on its own. When you buy the product you get the silicone and its catalyst together. Mix up as much (or as little) as you need and then pour them to create your cured rubber part. You can use the rubber to make a silicone mould (which you could then pour casting resin into) or to make rubber parts themselves (which would normally mean pouring the liquid rubber into a rigid mould).

Pretty much the only material silicone will stick to is other silicone, so a release agent is needed. A thin smear of Vaseline (which can be thinned using methylated spirits) or a spray wax called Macwax make effective release agents when you need to release silicone from silicone.

CS25 does not build up heat during the cure cycle.

Yes, silicone does stick to some kinds of Glass. You will need to use a release agent on Glass objects to aid the release of the silicone.

Yes, silicone does stick to porcelain. You will need to use a release agent on porcelain objects to aid the release of the silicone.

Yes, the mould can most certainly be used more than once. Exact lifespan depends on type of resin used, shape of the cast and other factors, but typically for most resins you would expect 10-15 pulls from the mould before it degrades and becomes unusable.

Yes you can use the CS25 for casting concrete into it. It is quite a flexible silicone so the mould will need to be supported to help stop flex and improve mould life. If you need a very long-life mould for casting concrete then an alternative would be our PX60 Flexible Polyurethane; this is often used for high production volume concrete moulds.

CS25 Condensation cure silicone has a working temperature range from -60°C up to 250°C.

At 20°C, 1kg of mixed Condensation cure silicone will have a volume of approximately 890cm³ (0.89 litres)

In the spec for the Addition Cure Silicone rubber the demould is 24 hours at room temperature but 2 hours at 60 degrees. In the spec of the CS25 Condensation Cure Silicon Rubber, it simply says demould in 24 hours. Is it safe to assume a similar 2/3 hours at 60 degrees?

No. Unlike addition cure silicone rubber, the cure speed of condensation cure silicone rubber (such as our CS25) is not increased with the addition of heat. Condensation cure reactions actually need some ambient moisture and so you will often find that using an oven to try to speed up the cure has the opposite effect and actually slows down the cure of condensation cure silicones.

Unfortunately not due the moisture content in condensation cure silicone's meaning it would likely make the resin cloudy and possibly not cure properly. A better alternative is an addition/platinum cure silicone such as our Addition Cure Silicone Rubber.

The only exception to this, is our range of GlassCast Clear Epoxy Casting Resins which have all been successfully tested and work well with our CS25 Condensation Cure Silicone.

No, we don't currently have a thixotropic additive for this Condensation Cure silicone rubber. We do have a Thixotropic Additive for our Addition Cure Silicone Rubber though; using these two products you would certainly be able to brush them onto a cornice, in position (even over your head) and take a mould of the detail quite easily.

No, our CS25 is opaque and grey once cured. If you need a translucent silicone then our Addition Cure Silicone Rubber is translucent once cured.

No, this is not 'food safe' or FDA approved silicone so it should not be used for food use. Furthermore, it's normally 'Addition Cure' silicone rubbers that are used for food applications (although we don't carry any food-safe silicone at this time)