Instructables

Silicone thinners; what is a suitable compound to thin silicone caulk? Thank you.

Preferably non-toxic and inert, to make the silicone caulk/gel more viscous, to allow it to flow into a mould more readily.

Do you mean LESS viscous ?

I've used a few % of silicone oil to reduce the viscosity, but it does make the rubber softer.

Better still, get a proper two-pack rubber.
brendanmccloskey (author)  steveastrouk2 years ago
Hi steveastrouk

Sorry, my misunderstanding of viscous was "runny" or "liquid", now I know it means the opposite, so you are right; what I want to do is make this translucent silicone gel more runny or free-flowing AND softer. Can you recommend an outlet/website for silicone oil?

Thanks
NasirU1 month ago

use petrol "gasoline" (fuel use in motor cars etc.) only problem is smell of petrol. I used this trick and it work.

Where are you in the world Brendan ?
brendanmccloskey (author)  steveastrouk2 years ago
Co. Down, N.Ireland UK
I've seen suggestions for methylated spirits, and also citrus oil. I'm hoping for something non-toxic, touchable and inert

Thanks
Brendan
PM me, and I can send you a small tin from work to see whether it works.

Two-pack isnt' that expensive though. I buy mine from Alex Tiranti in Reading.

Steve
canucksgirl2 years ago
On this website forum topic, a member posted very detailed information and advice about using silicone for molds and suggests different additives based on the type of silicone you are using.
brendanmccloskey (author)  canucksgirl2 years ago
thank you, lots of info here
I have done some experimenting with this, and I claim there are two tricks required for casting a large volume of silicone caulk. 

The first trick is to find some way to introduce small amounts of moisture (water) into the whole volume uncured silicone, because some small amount of water is needed as part of the reaction which cures the silicone.   If there are regions completely devoid of water, these will not cure, resulting in a volume that is cured on the outside, but uncured and squishy on the inside. 

One way introduce small amounts of water into the entire volume of your mix, is to mix in a drop or two of acrylic paint.  I have also read rumor of small amounts of glycerine (glycerol and water) used for this.  One advantage of using a few drops of acrylic paint is  that this provides a visual indicator for when you have the paint and caulk completely mixed.

The second trick, for the thinner, I have read of people using naptha, or xylene, and I have actually tried naptha, and it seemed to work, but of course it smelled terrible, like gasoline. 

I am guessing that part of the magic with solvents like those, is that a lot of the solvent will just evaporate completely, and not become a permanent part of the cast.