Silicone compatibility question

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TMBountyHunter

Well-Known Member
So I've gotten myself into a bit of a situation. I was gonna recast a small part today but found my OOMOO 25 has gone bad on me again. I have a terrible habit of buying a pint, using half of it fairly quickly and then leaving the rest for a few months because I have nothing else to cast. By that time Part A is too thick for pouring. (I'm too cheap to get that gas blanket spray, thought it looks like that might be a worthwhile investment). Last time this happened I just chucked the silicone. This time I thought I might be able to use it as a brush-on application instead of pouring.

That worked. The only problem is I didn't really have enough for a full mold, at least I don't think I do. Currently my mold is only a mm thick in some places.

So the question is: If I go and get Rebound brush-on rubber, will it stick to the OOMOO? Or should I just get more OOMOO and let it sit for a while after mixing so that it's thick enough to brush?
 

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exoray

Master Member
So the question is: If I go and get Rebound brush-on rubber, will it stick to the OOMOO?

It won't stick, and WORSE it won't cure!!! Platinum cure silicones won't cure in the presence of many contaminants, and tin cure silicone is a contaminant that will cause cure inhibition...

Or should I just get more OOMOO and let it sit for a while after mixing so that it's thick enough to brush?
That might work...

Or you can support mold the silicone (plaster or resin/fiberglass) and make a glove mold supported by the ridge support mold...
 

TMBountyHunter

Well-Known Member
Gah I completely forgot about the platinum/tin difference, thanks.

Guess I'll pick up more OOMOO tomorrow, I'll try the waiting and brushing first and if that doesn't work out too well I guess I'll go for the glove mold.



EDIT: GRRRRR Labor day tomorrow, stores closed :(
 
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TMBountyHunter

Well-Known Member
Ok so Labor Day was setback #1

Setback #2 is that the local supplier is out of stock of OOMOO 25 for another week so another question arises:

What's the best thing I can do to ensure the layers adhere to eachother a week from now? I've put a plastic bag over it for now to keep the dust from accumulating. Should I clean the "old" surface with something before applying the new one? Or do I just leave it and pray?

Sorry about all the questions, I just want to be sure I'll do as much as I can to not screw up the 2nd mold for this project
 

Pilot

Sr Member
In my personal experience, OOMOO sticks to itself quite readily. I made a mold several months ago where I started with some that was on the brink of badness...I used that to brush in the details since it was a little thick, let it cure, and then went over the whole thing with a brand new batch. Aside from the slight color difference between the two batches, you'd never know it was two pours. I've also used chopped-up pieces of old OOMOO molds to use as filler in newer pours with no problems.

Exoray and I have talked about this same thing before in another thread, and I was quite surprised to find that not all silicones stick to themselves like that - but my experience with the stuff is pretty limited compared to a lot of folks here. If you're not learning new things, you're not doing it right! :)

As far as ensuring a good bond between the two, just rinse the existing mold off under water if it's dusty and make sure it's 100% dry before pouring more on it. Shouldn't have any trouble after that - as long as you are indeed staying with the same product.
 

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