Thread: silicon mold material - does it weather and die??

Unfortunately they don't last forever.

The softer silicons tears easily, more so as it gets older, especially if not treated with respect. Pull on the sides to get the blanks out too hard and they will tear at the corners or worse still, the plugs tear off. Bond release helps, provided you don't get any on the tube, or trying to cast something apart from pure resin. The only other alternative is using a stiffer silicon, that usually costs more, and makes it harder to get your blanks out.

Tears can usually be fixed however with a bit more silicon on the torn surfaces and let it cure properly.

I also use the resin saver type molds that use rubber stoppers through holes in the ends of the mold, at least there are no plugs to tear off, but can still tear at the corners etc. Alternatively, make your own and use rubber stoppers and molds with thicker sides.

I have some moulds made by newlondon (pink ones) and some by ptownsubbie (blue ones)

The pink ones I have had much longer and get the most use, only 2 have just started some signs of tearing in the corners.

The blue ones have had very litlle use and nearly all of them have torn to a greater or lesser extent. The only ones that haven't torn yet are the vertical round moulds.

I don't think it is only a matter of which silcone is used, it also seems to be a matter of wall thickness, the blue ones, especially the tube-in moulds, have quite thin walls.
But one of the blue ones is a 4 blank 7/8" mould and it tore quite quickly, the wall thickness on this is quite thin IMHO.
That mould also developed some quite large bubbles.

It all depends on what you are casting in them. There are silicon rubbers made that are intended for use with polyester or polyurethane resins, and these will last for hundreds of casts, but the silicon rubbers that are not intended for poly-whatever resin will last less than a hundred castings even if you use a barrier coating such as green soap or Vaseline. Those numbers are for continuous use, I suspect that the chemical reactions in the silicon rubber mold caused by the resin curing by products keep on happening even if you are not still pouring new resin in.

If you want to keep making the same shapes, I'd suggest keeping a set of the best castings then going to someone like Barnes Products (in Sydney, on-line) and asking for a silicon rubber formulated for whatever type of resin you are using. Weigh you original molds then order the next size larger 'kit' of silicon rubber. and a pack of 'Kleen Klay' to seal your mold box (rob the kids leggo for blocks while you are it). There is plenty of information on line about making your own molds (and a lot of rubbish) so there is really no need to buy one of the booklets that are being offered.

Hirst Arts has a pretty comprehensive guide to DIY molds at:
Hirst Arts Mold Making Page

i have just started using Vaseline mixed with white spirits for a mold release, works pretty well, it also acts as a seal around the nipples to stop the resin from entering the tube

the white spirit disolves the vaseline and alows you to spread it more evenly, then let it dry, i have found no ill effects to the resin at all

the molds i have are the larger ones which do 4 sets of blanks, not the singles, i wonder if the smaller singles have the same problems

the molds have not had a lot of use, 3 or 4 castings in the cigar but a couple more in the siera molds, the molds are around 3 years old i just haven't used them

i must also say that i used the molds yesterday to cast some blanks, the amazing part is some of the cracks/splits are on external walls but there was no resin leakage at all, i was expecting a small amount, the resin must be too thick to run through

the nipples on my molds are also a different color from the body of the mold which makes me think that they were cast separate then held in place to be cast, this maybe why some have broken off

i am thinking of making some for myself, i like the plug idea but have not been able to source any locally, can anyone point me in the right direction

do you think that a thicker outside wall is better than a thinner wall, in my estimation the thinner wall would be more inclined to bow from the weight of the resin but should be more flexible when demolding, the thicker wall would be more rigid but less flexible and more likely to crack. the thinner wall could be stabilized by making a little box of the correct dimensions to support the walls while casting

thanks for taking the time to read and add your thoughts

all the best

MIK

Whilst Silicon (RTV) is a natural release, the heat the the chemicals in PR will cause it to go brittle over time, also sunlight does not help as the UV will break down the silicon.

I have found the Vaseline+white spirits to be good, but can't be bothered mixing it, so instead I use WD40 until I was a bit short of cash and found RP7 was $2 cheaper. now after each casting I use RP7. I give them a quick spray and wipe round with a tissue then if I'm not going to use them again they go into a paper bag and then the draw (out of the sunlight)

I must admit I only use Ultrasil and find I get a LOT (100+) castings out of my moulds. so far touch wood it has only been the early moulds that never had a release agent (WD40, RP7 or Vaseline) that are splitting - but these are nearly 2 years old..

Mark

Well I have like reading all the info that has been posted here because I too do a little bit of casting and had mixed results with molds. I purchased a few or the large mold from New londen in a group buy I did some time ago (Maybe 2 years but not sure) and never used them at all then about 8 months ago I started to use them and guess what ? the dam nipples started to break off on the sierra mold that I had. I contacted New London and asked if there was a problem with the molds and was told no that they just wear out (Without use ?) so I then started to make my own and thinks seem to be working better. I have made my molds thicker and that seems to have made a difference. The subject has come up before about what colour mold is best so just because of the stirrer I am I then made the molds in different colours if you haven't seen them I will add them below but please realize that because they are thicker they have all cost me a reasonable amount in particular the Sierra mold.

Cheers Ian

Ian,

You have been busy making all these molds and may I say a very colourful display what silicone have you found to be the best and is it one of the more expensive ones or one of the cheaper ones? and where do you source it from any links?

Cheers
Tony.

Just the cheaper one off Ebay Tony, although he adds some colouring dies to make it interesting

Originally Posted by dai sensei

Just the cheaper one off Ebay Tony, although he adds some colouring dies to make it interesting

What He said LOL



Cheers Ian

Originally Posted by AuS MaDDoG

Ian,

You have been busy making all these molds and may I say a very colourful display what silicone have you found to be the best and is it one of the more expensive ones or one of the cheaper ones? and where do you source it from any links?

Cheers
Tony.

mine arrived today not sure if this is where the others get theirs but it is the only one i could find HERE

i haven't even made masters or molds as yet

Question for Neil,Dorno or Ian

i am planning to make the nipples the same size as the drill used to drill the blank, is this big enough or do i need to make it slightly bigger again to get the seal right so resin doesn't leak into the tube??

thans in advance

MIK

No No No Mik going by my past experiences I have always drilled the holes for the nipples the size of the inside of the tubes because any bigger and I think you will have trouble getting the tubes over them ? I could be wrong but I have done all of mine like this with no problems Except I have not tried them under Pressure so I am not sure How they will got that way. I await the masters (Dai Sensai) Comments I am sure he will have the correct answer.

Cheers ian

I got mine HERE Neil too I think I try and get tapered holes for the nipples to give some wriggle room just open up the front of your drilled hole in the master you make to get a plug effect , cheers ~ John

Originally Posted by MBUMIK

i am planning to make the nipples the same size as the drill used to drill the blank, is this big enough or do i need to make it slightly bigger again to get the seal right so resin doesn't leak into the tube??

That is what I did, ie same as drill size for outside dia of tube, but with a taper to help fitting. But my later ones I just made a hole, then used rubber stoppers (from flebay) to fill the hole/tube, as are the more recent designs.