Clear and reliable advice for working with silicone rubber

I’m sorry to say that the purpose of this short posting is not to ‘give it’ .. at least not yet .. rather, I’m turning the tables just for once and ‘asking for it’!

For example, if anyone can recommend sources of information they’ve relied upon in their practice I’d be interested, particularly in those that go into a little bit more detail or even those that are a bit more exploratory. I try to provide clear guidance here, but I haven’t really organized it all into one place yet, and I’m trying to get my facts ‘straighter’, and maybe pick up some more tips from others, before I do. The information provided by manufacturers should always be the first ‘ports of call’, and some suppliers do have some reliable ‘how to’s on their websites .. but maybe there are some I’ve missed along the way.

David Neat, mouldmaking and casting, Lukasil 429 and catalyst

I’d also be interested in what you have experienced regarding ‘shelf life’ i.e. how long you’ve continued using the components before the mix behaves differently to when you first got it? How did that compare to the supplier’s advice? Were you given a clear statement of shelf life in the first place, or did you have to hunt/gather to find it? Worst of all .. did you only find it written on the product once you’d got it? You see, it’s basically evident that suppliers or manufacturers show rather dubious behaviour when it comes to owning up to shelf life. Also, have you ever tried the ‘unthinkable’ i.e. tried a silicone rubber with a catalyst not intended for it? I’ve never had any catalyst going spare, and you probably haven’t either .. but if anyone has done, I’d be very interested in what happened?

David Neat, mouldmaking and casting, making a silicone mould in coloured layers

I recently did some tests which confirmed what I’d always suspected (or maybe read at some point in the past, because I see it is mentioned very occasionally) .. that however old the silicone ‘body’ might be, as long as it moves when you tip it, you can make it work by getting some new catalyst. I tested remainders of silicone which had been shoved in a corner waiting to be taken to the Recycling Centre, some going back more than 7 years .. and they all worked! Yes, they were different .. they were much more viscous than they should have been; the working time was much shorter, and they cured in no time at all! .. but still good for some things!

David Neat, mouldmaking and casting, making a skin mould on shaped styrofoam

When you’ve bought a silicone has it come with the essential facts i.e. not just the ratio of the two parts to mix, but the following: .. its weight in grams per cubic centimetre (good to know if you want to work out how much you’re buying in volume); its viscosity (useful when making a choice, because thinner ones could flow into detail better and leave fewer air bubbles); recommended cure time, etc. Has your supplier even said .. most importantly .. whether it is an ‘addition cure’ (platinum) or a ‘condensation cure’ (tin) silicone? This is important because whereas condensation cure silicones nowadays are fairly unaffected by anything, ‘addition cure’ silicones are a different matter. Or .. are they really? At times I’ve treated addition cure silicones really carelessly in the past without any problems. Again, any personal experiences would be welcome!

You see what I’ve done here? In asking the questions I’ve given information at the same time .. think of it as a standard teaching technique, though reversed in this case. Nevertheless .. I really do need other people’s help on this subject, so any facts you can contribute would be much appreciated!