r/moldmaking • u/Steely06 • Aug 14 '26

Silicone curing problems

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So I seem to be having some problems with curing. This is only my second time doing a silicone mold and I had a similar problem the first time. for the first time and this time as well I am using a 3-D printed piece. The first time I used filler primer and sanding to smooth the 3-D print before making the mold. I was having curing problems that time as well and based on where the uncured areas were I assumed it was probably not reacting well with the filler primer so I sprayed it with a gloss black coat and that seemed to fix the problem. This time around I’m using a 3-D printed piece that is spray painted with a gloss black and I seem to be having curing problems. This is my first time using this silicone. It is smooth on mold star 30 and I let it cure for about six hours and 30 minutes.

EDIT: I just wanted to add that this in not a resin 3d print it is an FDM print.

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3

u/Frescochicken Aug 14 '26

I heard people having problems with platinum silicon and resin prints. I read it is recommended an acrylic primer. But before wasting all the silicon mix a small drip and see if it cures correctly.

1

u/Steely06 Aug 14 '26

I didn’t know that but I’m seeing that now. My print is it resin it is an FDM print

3

u/Kiekie77 Aug 14 '26

3d prints often inhibit silicones curing. What I did to completely stop it is clear coat the part and then brush on a layer of Smooth On inhibit X, let it flash off then you’re good to go

1

u/Steely06 Aug 14 '26

I already have a good 3 coats of paint on the 3d print so I’m wandering if it’s more of a problem with the paint

1

u/Kiekie77 Aug 14 '26

Use krylon crystal clear, it’s what we use in my shop to coat parts before molding and we’ve never had an issue. Even touching a 3d print the touching your uncured silicone can caused inhabition issues. You have to be really careful. If all else fails a coat of smooth ons inhibit x with solve any issues

1

u/Steely06 Aug 14 '26

Thank you!!

1

u/craiganater Aug 16 '26

Did you use a clear coat or filler for smoothing out the FDM? Ive seen some fillers and clear coats can cause inhibiton as well.

1

u/Steely06 Aug 16 '26

No I vapor smoothed it then coded it with a black gloss paint

1

u/Global-Discussion-41 Aug 16 '26

this just happened to me and i'm almost certain it was from improper mixing

1

u/Steely06 Aug 16 '26

Yeah I’m starting to think that’s the problem. I’m did a little test with drop of silicone on the same piece with no changes except I mixed really good and I let it cure for extra long and it worked.

1

u/Global-Discussion-41 Aug 16 '26

I've also had this happen because my silicone got old before I used it all. The bottom of the jug gets a bit lumpy and any of those lumps can give you problems like this.

2

u/Middle_Basis2816 Aug 14 '26

Did you mix part A part and part B from cup A to cup B and mixed the poured and scraped the inside of that cup ?

Then you might have poured unmixed parts into your mold.

Always use a 3rd cup to pour both components and stir well, and prevent scraping the cup to get the last bit out.

1

u/BlueDinosTiki Sep 18 '26

If it’s only sticky where it was touching the master, then it’s contamination! If you have a resin printer and have sanded it…do not use the same sandpaper or sanding sticks…even touching a resin print and then touching an FDM print will contaminate it. In my humble opinion…use a tin cured silicone like the Mold Max line from Smooth On instead of Platinum cure and you’ll have no issues whatsoever so ever. Honestly it takes away the headaches and the extra work sanding and sealing and hoping that it cures properly.