how to smooth rough silicone

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mgriffsgirl

New Member
I am trying my hand at this silicone baby stuff for the first time ever. Its going ok except I am learning on my own and mostly guessing. I have completed my molds and made the body parts and some of them are rough and some have airbubbles. To fix the rough parts, I have seen people use sandpaper so I got the 1200 grit wet dry but its not smoothing at all. It leaves lines in it, someone please let me know how to smooth silicone out with something I have around the house!
 

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8 perf

Sr Member
I'm guessing you actually mean smoothing the resin cast parts that came out of the silicon mold, correct?? Do you have pics of what you are working on? What type of resin are you using? Not sure why the cured surface would be rough unless there are a lot of air bubbles floating on top. Need a bit more clarification to help you out.
 

mgriffsgirl

New Member
20150120_145702.jpg this is the silicone part that I a working on. Its platsil gel 10 with a bit of flesh color. As u can see I am sanding t noe because the surface did not come out smooth. Is there an easier way to get the surface smooth rather than sand with 1200 wet dry?
 

8 perf

Sr Member
I've actually never heard of sanding silicone rubber before. I usually make molds with silicone and cast a hard resin piece inside. The mold master is usually glass smooth to avoid imperfections. You are doing the exact opposite, for obvious reasons. What sort of surface texture does the inside of your mold have?
 

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8 perf

Sr Member
As I said, I've never done that before. I make silicone molds and cast into them, not silicone castings. The only thing I can think of is the inner surface of your mold has imperfections in it, or perhaps the silicone was not mixed smoothly enough. Just spit balling. Those are the two things that come to mind. I don't know if acetone or lacquer thinner will have any affect on silicone or not, but you may try smoothing it with a cotton swab on a small part that might not be noticeable. My next guess would be to contact the maker of the silicone and ask them for advice.
 

PoopaPapaPalps

Master Member
RPF PREMIUM MEMBER
Yeah, I've never heard of sanding silicone either. If there were imperfections on the surface of the silicone that aren't trapped bubbles, then it was either on the surface of your sculpt or whatever it was you've molded or the surface of your negative in your mold, itself. Given I don't know what material you made the molds from (Plaster? Fiberglass?), my recommendation is if you still have the original positive, fix it up until it has the surface finish you want and remake it because I don't think you can sand silicone to a smooth surface.

I'd suggest making some more silicone and lightly spreading it over your silicone pull and try to smooth out imperfections like that, but 1) it's a stinker to do because you'd lose detail and 2) it's very easy to mess it up; wasting time, money, and effort.

Try detailing what your process has been and maybe that can help us help you.
 

swgeek

Sr Member
Yeah it looks like your mold has a lot of surface bubbles and when you cast the other silicone in the mold it filled all those bubbles, and left you with a pimpley surface. Not much to do for that except try and recast your part, or more likely, make a new mold.
 

camerafx24

Active Member
RPF PREMIUM MEMBER
It would appear you have tiny air bubbles in the mold surface. If you were to make your molds out of epoxy (smooth on carries it) you wont have this problem. also, are you de gasing your silicone? It wont solve this problem, but will make for a better casting.

I hope this helps.
 

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detenten

Active Member
Judging from your picture, I have pulled a similar looking casting of Dragonskin out of a Rebound 40 brush mold.

My guess is you did this: you have a sculpt, you brushed on a silicone, and then cast silicone in silicone-- but your end product has holes on it.
This could be a result of your mold-- what happened to me is I used too stiff of a brush, and in trying to push Rebound 40 into the crevices of my sculpt, I poked little holes in my clay sculpt. So my mold ended up with whispy hairs on it that gave me some mangy looking castings.

It also resembles a silicone casting I took out of a rough quick plaster lifecast I took of my face-- the air bubbles and rough nature of plaster gave me a pitted resin casting and bumpy silicone copy, too.

I think your problem is with your mold. Look at the inside surface and see what it looks like; if it's rough, then your casting is going to be rough. You might need to make a new mold.


If the above is not your situation at all, then try this:

Thin your casting silicone with silicone thinner. For some reason your casting rubber might not be reaching all the small places in your mold and so you're missing some detail, or it's forming bubbles for some reason. Also try using a soft brush to brush on a first thin layer of silicone in your mold to capture surface detail, let it cure to "tacky," then pouring the rest of your casting.
 

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