Norski Silicon Moulding Rubber - HELP

[Dan]

Not sure if this is widely available but as I'm having trouble with it I thought I'd ask here .

I was trying to make some moulds of a small terrain piece for my Dads Army project . I mixed what I thought was the correct ratio but it never went off . I then mixed some more hardener in about a week later and it started to go off . This has still never actually set in about three weeks of sitting in the airing cupboard. The mixing tray sitting above my bench is about as wet as the original unmixed state.

I have about half of the hardener left and about 90% of the Silicon . I'm thinking it could be temperature but am unsure.

The depth of the mould was only about 5mm . I managed to remove the master and cleaned it up with Laquer thinner so am ready to have another attempt.

Any ideas ?

[archangel1]

How old are your products? I think that the shelf life for silicone is only about a year and the catalyst seems to disappear long before that.

[geronimo]

If the catalyst is mixed in correctly and the mix is left at room temp or above, it should always cure eventually.

As already mentioned, though, shelf life may be an issue. A bad batch is a possibility. If the catalyst wasn't thoroughly shaken before adding to the rubber it could also affect the cure. Did you wear latex gloves when mixing? - the latex can affect the cure (always use vinyl gloves with silicones). A final possibility is heat - too hot and the catalyst can evaporate out of the rubber - though this only applies to condensation cure rubbers.

[Dan]

The Silicon was used a couple of days after buying it , so hope its not too old . I did'nt think to shake the catalyst so that could be it . I did'nt use any gloves .
I have used a red silicon before with out any problems .

I will give it another go on a warm day with a much smaller mixture .

Thanks.

[Ramshackle_Curtis]

Sounds wierd, Ive never had any problems with silicone not going off. I use latex gloves and as long as the temperature is above about 15 degrees centigrade should be OK...

I think is a probalem with the catalyst. Ask the supplier.

[Dan]

I'm now wondering if it was the temperature . I'm pretty sure I had the work area at room temp before mixing  ,but it may have dropped before putting everything in the airing cupboard .
I'm a bit stuck as its winter now and I might have to wait for summer before having another attempt.

[Ramshackle_Curtis]

If you put the mould under a 60w lamp it should cure. It doesnt matter if you cast in a cold room, the curing will begin as soon as the silicone is at the right temperature. How warm is your airing cupboard? Im surprised it hasnt gone off in thier...

[Dan]

Hi thanks for the help .
The Airing cupboard is usually quite warm but my stepson does not know how to close doors  so I cannot tell if it was in there long enough to start the drying process . I also think I may have made the mistake of leaving it in the lounge too long before transferring it to the cupboard .

I think next time I will heat up the lounge and the mix the silicon up just before bedtime so it can start the drying process over night without being disturbed.