Hey guys,

I'm looking into casting converted pieces for an upcoming army - and have hit a brick wall.

So i went down to Barnes and the dude there was very helpful, and set us up with everything we need. I get home and do a trial run for a silicone mould of a space marine backpack. I measured up the ratios and mixed the two parts of the silicone. Within 8 hours, it was cured perfectly.

Now here's where the trouble starts. The second mold i do (with the piece i intend on casting) takes the silicone about 18 hours to cure, when it clearly states 6-12hrs on the box. I thought i'd not measured properly when mixing which created the longer curing time. I then do the next half of the mould (this time making sure everything was deadly accurate), and i waited for the silicone to cure. 1 day...2 days had past, and over 48 hours later i ripped out the master from the uncured silicone. It has set to a 'jelly' like state.

And, being persistent, i re-did the mold. Measuring again, then getting a second person to double check the measurements before i mixed. It's been over 2 days once more, and it's of a worse state than the previous one

Is there something i'm missing here? Do the two parts of the silicone need to be preserved? It doesn't say anything on the packaging or bottles?

Any ideas people?

I use Ultrasil Fast Cure.

Thanks,
Adam

Not one I've used so far. I've used a couple of Barnes' products over the last few years and nothing like this has ever happened to me.

Perhaps BlindPig can help. AFAIK, UltraSil is what she uses.

Grow your own man-boobs Adam, don't cast them in silicon.

Ask around at Western Suburbs, should be plenty able to give you advice on doing it "naturally"

Same can be said for your hair Bolesy

Could the humidity do anything to the setting process?

Perhaps. First one was indoors w/ air con. All the others were in the garage.

Do you know if its by any chance and endothermic process? Stick a thermometer into the next mould you do and find out. Would be interesting to see.

Hmmmmmm......Never had that happen with Ultrasil.

1. Check the expiry dates.
2. Ultrasil won't get hotter than about 68degrees when curing. The hotter, the faster the cure.
3. Are you measuring by weight (recommended) or volume? Check the batteries are working and the scale
is free to move up and down.
4. Ultrasil is a Tin Calalysed Condensation cured silicone. Moisture in the air shouldn't affect it curing (I live in the
subtropics and it dosen't affect the cure time at all)
5. Make sure the cups and stirring spatula is clean and free of grease.
6. Be careful with PVA glue on models, some silicones do not like it. Ultrasil is usually good with PVA
7. What have you used as the release agent? If you use the Barnes stuff (Rapid release etc) then it should
be OK, but you should wait for it to dry completely before pouring the Ultrasil.
8. Ultrasil should be 100 grams ultrasil Part A to 10 grams part B Catalyst (just in case).

If you can answer all these as having been done or covered, then I guess give the Barnes people a call and see if they have any further clues........

[edit] The only time I have ever had a silicone not cure, was the Dow Corning White RTV Platinum Catalyst stuff. It was *very* fickle about its' expiry date and wouldn't set about 6months before the expiry date.


Welcome to casting!!!!!! Leave your wallet at the door

^^ x2

I'm further north than Blind Pig and I made an Ultrasil mould during our stinking hot, humid weather on the weekend. It turned out beautifully and actually seemed to cure faster than normal.