silicone mold question

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ScoobiJohn

Active Member
ok my first 2 part mold and well part two leaked.... :( but onwards i know the only thing silicone really sticks to is itself - does that mean i can attempt a second pour without removing the remnants of the first as (last time i checked) still fair bit of silicone in there (is a 24hr setting one so who knows how much there will be in another 16hrs)

basically i'm worried that in removing the second layer i will upset the position in the first

any advice?
 

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AKA Pablo

Jr Member
Can you? Yes. Will that give you the best result? Almost definitely not. Even if it does adhere you're most likely going to get a witness line in there somewhere. Whether or not that matters depends a lot on your mold.
 

PlanetAlexander

Active Member
Are you able to send through a photo of the situation? I recently had a bad experience with a two part mold too but in the end I managed to fix it so I might be able to help.
 

robstyle

Master Member
If there is a thin layer of cured silicone on the part you may or may not end up with an orange peel effect when adding more silicone. Sometimes that thin layer will peel off when cured, sometimes it wont. Is it worth the what if chance and the $$$ behind it, or do it again? As mentioned, a picture tells a thousand words.
 

ScoobiJohn

Active Member
ok so things haven't changed much since last night - there is only a tiny bit exposed - ok for second pour?

PSX_20200406_102647.jpg
 

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PlanetAlexander

Active Member
Personally I don't see the problem with pouring over the top of it, as long as you seal the edges of the container really well. Probably best to get the second opinion of someone with more expertise, I've only done a couple of molds.

You might even be able to reuse some of what leaked out. You can put it into the mold to save new silicone that needs to be poured. If it's cured where it's leaked, I'd say it'd be safe to put it in the mold.
 

xeno

Sr Member
pouring on top won't be a problem,
but the tiny bit sticking out might be, the thin layer of silicone might not be hardening properly and could still feel sticky, this can ruin that part of the mold, as that sticky bit gets encased inside the next pour, and create deformation or wet silicone in your copies.

Check if it feels sticky, if it feels non sticky and hard then there is no problem pouring a second part.
 

JBReplicas

Sr Member
Hot glue over the seams of the box again and then tape over that once it’s cooled down, then re-pour it, should be completely fine.
 

ScoobiJohn

Active Member
the silicone does seem to be set properly but the bit sticking out the silicone is very thin if i bonds with the next layer it should be fine (although since silicone obviously leaked down the sides probably going to have to cut it open :( ) anyway will give it a go and see how it turns out - thanks for the advice and next time i'm not going to reuse the foam core :)
 

ScoobiJohn

Active Member
little update - second pour worked perfectly - wouldn't know i had done one to look at it - now just have to fill it :) and hope that one doesn't leak as that would be much harder to clean up the mess

thanks for the advice - helped me out when i was panicking
 

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sjanish

Sr Member
RPF PREMIUM MEMBER
little update - second pour worked perfectly - wouldn't know i had done one to look at it - now just have to fill it :) and hope that one doesn't leak as that would be much harder to clean up the mess

thanks for the advice - helped me out when i was panicking


Good that it worked out.

If you are going to add more silicone, the sooner the better. I've had similar short pour problems before and have mixed up more and added it within an hour of the first mix/pour. I have never had an issue with it not curing as one. The couple of times I have added more silicone to fully cured silicone I have cleaned the cured silicone with denatured alcohol, let it totally evaporate before pouring. I have been lucky, it has worked every time. Still, I expect it could go wrong the next time I try. You never really know.

Someone else already mentioned hot glue. Keep a warmed up glue gun close by when you are pouring. If you notice a leak stop pouring and slather on hot glue to seal the leak. Pour your molds on cardboard or old newspaper to make glue or silicone cleanup easier. I once used 3 sticks to seal up a really big leak...it was an unconventional mold box, long story. Hot glue is much cheaper than silicone, the mold turned out great . I normally use styrene or cardboard to make my mold boxes and use hot glue to seal them. Denatured or isopropyl alcohol will make the hot glue release from most materials once the RTV is cured.
 

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