Thread: First Silicone Mould

Originally Posted by BoomerangInfo

Hey, do you know, once you have a set silicone mould, can you cast silicone into it, or does silicone stick to silicone, if you get my drift?
Russell.

Silicone doesn't stick to much of anything EXCEPT silicone!

You need a special type of release to get it not to stick. I'm not sure where to get it,
but I know I've seen suppliers mention it.

Silicone RTV does stick to itself, in fact it is the only thing it will bond to, and it will not let go. This is useful in that you can chop old scrap RTV up finely & use it as 'filler' in non critical parts of a new mold.

However you can use a number of things to get RTV to release/not stick to itself - the easiest is to just rub some Vaseline/petroleum jelly over the area not to be bonded. Make sure you get some down the outside of the mold too, not just the part line as RTV can creep into tiny spaces & glue things together.

You will find that when making a 2 part mold it is quite hard to get the parts to separate as there is a very exact mechanical fit which makes it seem like it has set solid - did you remember the parting agent? - then suddenly it lets go. One shop I know just casts the mold in one piece with steel locating pins thru both halves, then cuts one side of the mold thru' to the master inside. When you can release the master you have cut far enough - but the master has to be either very hard or expendable for this to be viable.