Comment on DIY casting silicone from caulk, pourable version by Prince

Our post from three weeks back about Instructables user mikey77's “Oogoo” formulation generated some really great discussions in the comments. Now, reader Iceman086 has reported some successful experiments combining caulk, cornstarch and a solvent to make homebrew silicone with a pourable consistency. Perhaps we can call it “Ooze-oo?”

I found that when making a mould you can use a 4 to 1 ratio of paint thinner to caulk (2 oz of caulk to 1/2 oz of paint thinner) to make a small mould using the bottom of a plastic cup. I added in about 3 drops (literally drops) of paint to the mix in order to help show the details of the mould. Once I had a consistent mix of paint thinner to caulk I added in about 1 tbs of corn starch as the hardening agent. This gave me about 5 to 10 minutes worth of pot time and fully set within 45 minutes.

I gave it an hour and a half just to be sure before I mixed up some casting silicone. This time I used a ratio of 3/4 to 1 (silicone to paint thinner) in order to get a mix that was able to flow. You can go 1 to 2 (silicone to paint thinner) if you want a thinner mix that is pourable but its up to you. I added in my paint (again 3 drops but yellow this time) and mixed until the 3 parts were consistent. I then added in 1/2 tbs of corn starch to the mix as a hardener. After doing this though the mix thickened and I ended up having to spoon it out. This batch still worked how ever and I was able to get some very nice
results. The pot time was about 15 to 20 minutes with this mix and the dry time was around 2 1/2 hours.

If you want a casting consistency that is still pourable I would recommend using the same ratio of Silicone to Paint Thinner but you can reduce the amount of corn starch to 1/4 tbs. HOWEVER! Reducing the amount of corn starch will increase the set time.

In some of the posts above people talked about shrinkage. I didn’t see any noticeable shrinkage given the amount of paint thinner that I used.

His full comment also includes some interesting reports about his experiences with improvised mold releases. Well done, sir!

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I am descended from 5,000 generations of tool-using primates. Also, I went to college and stuff. I write for MAKE, serve as Technical Editor for MAKE magazine, and develop original DIY content for Make: Projects.