"recycling silicon rubber mold ?" Topic

have a couple of old and poor molds ,i saw last night a piece about a mold maker on the web, who cuts up all his old molds and adds them to new molds ,i am thinking of doing same
would this new mixed mold be as good as a original mold
and does it matters if the mold is made from different manufacturers silicone rubber

I'm guessing he's just using them as a filler.

Main problem is that it will thicken the mould so won't pour as well, won't give as good detail. Also, different rubbers may have different temperature ranges they can be used in.

I wouldn't risk it without testing first.

I chop up my old ones to use as filler (tip: larger flat pieces work better than tiny minced pieces) after putting in enough RTV to cover the items to be cast. Just be careful not to put it right on top of them. This basically "raises the water level" of the RTV to make a thicker mold. At $ 30+ per pound, I'm definitely going to use the old RTV to stretch my supply of the newer stuff. (Oh, and don't use silicon caulk as filler. It tends to distort a mold….)

It does have its drawbacks . If the detail is shot and the rubber is fresh and still has life in it then it can be used . If the rubber is old and brittle then do not do it , Older rubber can shorten a mold life . If the rubber is a different brand or sheer tear strength do not do it ,.
As a garage kit mold maker we used to do it alot but unless you are going to burn the mold out quickly it can be a touchy issue

As zephyr said, you pour a layer covering the master first, so there's no danger of losing detail. The filler just bulks out the mold volume, saving you rubber. With room temperature casting, there are no real issues with compatibility – won't work with vulcanized rubber at all, I would think.

It definitely shortens mold life a bit, but probably not enough to be a bad tradeoff compared to the cost of the rubber you save. I'd be careful about using pieces from the "working face" of an old mold – they'll be the sections most affected by age and heat, and therefore the most brittle. The backside, on the other hand, should be fine for use as filler – it takes a long time to "cook" all the way through.

I always found minced rubber worked fine, but strips or flats shouldn't be a problem either, and take less effort to make. You don't want to use too much filler no matter what – keep it down around 30% of total volume if the filler is old rubber, new rubber (from a botched pour) could easily go as high as 50% safely.

the best way is to mince the old moulds, mind you i have worn out 3 mincers doing this as an industrial one is quite rare and expensive.
trouble with large lumps is that they sometimes break inside when pulling the castings out of the mould and then they do not sit back together right again making them leak.

thanks guys
some of the molds used once ,mistakes made when preparing them
others about 8- 10 pours (metal)
ming31 when you say older rubber could shorten life of new mold how many pours would i get/lose rough numbers

also some molds will be used with resin should not be a issue then???

I did this once. Since silicone oils tend to diffuse, you shouldn't recycle "old moulds" if they are actually old, this would decrease the overall mould quality while appropriate mineral fillers wouldn't.

The number of decent pours you get depends on your silicone, the age and content of old silicone, and your conception of "decent". Even defining a lose number would be inaccurate. Try it ?

Cheers

I used some minced up pieces of a couple of small moulds to add some ballast to a couple of small block moulds I made today.They were not "old" moulds though ,just small moulds I wanted to use once for small detail parts….so still "newish" silicon in the sense they werent worn out.Making sure the "old" rubber/silicon doesnt touch the master model detail and you should be fine.Any really old silicon is not much use for reasons others have stated above.