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Author Topic: [help] Silicon mold gone wrong  (Read 590 times)

Offline Gabbi

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[help] Silicon mold gone wrong
« on: April 09, 2018, 11:09:46 AM »
I have done a couple molds od small bits I have converted. Single piece mold.
I am using Prochima stuff.
I have opened one of the molds and silicone is very soft and sticky. Pretty sure I have mixed too few catalyst.
I have another one still in the container I poured it.

A couple qquestions:

1) There is any chance that it will fully cure if I wait long enough? (approx 36hrs have passed now)
2) There is a way to remove the very sticky uncured silicon from the masters?

Offline OSHIROmodels

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Re: [help] Silicon mold gone wrong
« Reply #1 on: April 09, 2018, 11:15:14 AM »
I'd leave it in there for a few days near a source of warmth.

Depending what your master is made from there won't be a lot that will remove the sticky residue without damaging the master. Mentholated spirits (purple liquid) might be worth a go but try a test first.

Offline gnomehome

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Re: [help] Silicon mold gone wrong
« Reply #2 on: April 09, 2018, 12:57:14 PM »
Mentholated spirits (purple liquid) might be worth a go but try a test first.
My first try would also be an alcohol, be it methanol, (denaturated) ethanol or even isopropyl-alcohol.
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Offline Gabbi

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Re: [help] Silicon mold gone wrong
« Reply #3 on: April 09, 2018, 01:27:35 PM »
Thanks. Tried denaturated ethanol and didn't work.
Tried nitro and it destroyed resin bits.
"Luckyly" the only bit I really need to retrieve is in metal, so, worst case scenario I can go with nitro.

But first I'll try to warm up the rubber and wait a few more days.
« Last Edit: April 09, 2018, 02:59:12 PM by Gabbi »

Offline Fitz

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Re: [help] Silicon mold gone wrong
« Reply #4 on: April 09, 2018, 09:54:47 PM »
If the mix has any catalyst in it at all, it will eventually cure, but there's no telling how long it might take. Moderate warmth will help, as has been said, just as cold will retard curing.

I've never found any effective solvent for RTV silicon rubber that isn't frighteningly toxic.

Offline Finn

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Re: [help] Silicon mold gone wrong
« Reply #5 on: April 10, 2018, 09:41:09 PM »
          It has been a while but if I remember correctly, room temperature vulcanising rubber uses a dibutyl tin catalyst (or something like that).   

        While warmth will help cure the under catalysed rubber a dry atmosphere will not. Just sprinkling water over the back of the mould  of a damp rag will make a big difference.

Offline Gabbi

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Re: [help] Silicon mold gone wrong
« Reply #6 on: April 11, 2018, 04:52:39 PM »
Thanks once more.
I have heat up the container in wich I have poured the rubber. It is on the radioator at the moment, with a damp paper towel on the rubber.
It is not sticky anymore and if I press the container it feels quite solid. I think I'll leave it alone another day or so, then I'll remove it from the container.

Thanks everyone for suggestions and advice.

Offline panzagl

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Re: [help] Silicon mold gone wrong
« Reply #7 on: April 13, 2018, 04:25:28 AM »
When I took a silicone molding class they repeated several times that latex (like gloves) or sulfur in clay could retard the mold curing- is it possible this is your issue? 

Offline Dr Mathias

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Re: [help] Silicon mold gone wrong
« Reply #8 on: April 13, 2018, 04:49:16 AM »
When I took a silicone molding class they repeated several times that latex (like gloves) or sulfur in clay could retard the mold curing- is it possible this is your issue?

Right- a lot of oil based clay (Plasticene etc. used for holding the master model) has sulfur in it and it will definitely mess up the curing. Coating it with a layer of Future floor wax before pouring the silicone will seal it.

I had a mold that wasn't curing, tacky, etc. (likely because of the sulfur thing) so I put it in a cardboard box and set up a blow dryer to force warm air into the box. Just make sure it has an exit point or the dryer will overheat.


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Offline Gabbi

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Re: [help] Silicon mold gone wrong
« Reply #9 on: April 14, 2018, 09:17:25 AM »
I have opened the mold. It has cured, but it is full of tiny bubbles (not around the model, just the part that was on the bottom of the plastic cup I used.
Don't know it it will be usable, I'll try to cast one. Anyway, I was really interested in retrieving the master, and it came out of the rubber undamaged and without sticky goo on it, so I'm happy as is.

What I have done:
1) wait almost a week (poured the rubber on Saturday after lunch, removed from the plastic cup on Friday night).
2) warmed up the mold. First I have dropped it on a pot with hot water (put the pot on the stove, brought it to boiling point, removed from the stove, put the mold in it). Replaced hot water multiple times, like 3 o 4 times.
3) Left for one working day on a hot radiator at work, with damp paper towel fit in the cup. At the end of the day the mold felt stiff through the plastic cup.
At that point I just decided to wait till the weekend to open it up.

Thanks everyone who helped! :)
« Last Edit: April 14, 2018, 09:20:10 AM by Gabbi »

Offline OSHIROmodels

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Re: [help] Silicon mold gone wrong
« Reply #10 on: April 15, 2018, 07:54:04 AM »
Glad you were able to save it. I've had one or two mould mishaps over the years and it can be quiet disheartening.

Offline Dr Mathias

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Re: [help] Silicon mold gone wrong
« Reply #11 on: April 16, 2018, 12:48:12 AM »
My most unpleasant casting experience was pouring resin into a mold, then realizing that I had neglected to mix part B into part A.

 o_o

Offline nic-e

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Re: [help] Silicon mold gone wrong
« Reply #12 on: April 16, 2018, 02:03:53 AM »
Be thankful it wasn't a bronze mould. There's nothing more terrifying than having a jet of steam followed straight away by a sizzling "BANG" as you get covered in hot sand thrown up by an exploded mould.  lol

I've got more than a couple failed silicone moulds on my shelf. I keep them as reminders of what not to do in future ;D
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Offline Hammers

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Re: [help] Silicon mold gone wrong
« Reply #13 on: April 16, 2018, 08:23:08 AM »
When I took a silicone molding class they repeated several times that latex (like gloves) or sulfur in clay could retard the mold curing- is it possible this is your issue?

Interesting.

Offline Rich H

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Re: [help] Silicon mold gone wrong
« Reply #14 on: April 20, 2018, 12:48:14 PM »
Or realising thald way throuhg a pour of a second half of the mould you've forgotten the mould release...  master now encased in a block of silicone...