Easy making a mold with Liquid silicone rubber
A and B component
The Liquid silicone consisting of 2 components, A and B. If these two are mixed together, the liquid silicone will be hard. With an addition of 5% hardener (hardener = B component), it will take 24 to 19 hours before the silicone has cured. You can add more hardener but you with the risk that not all the air bubbles are out of the mold before the silicone has be hard. The hardener weighs less than a gram / ml and the silicone more, it is important to determine or you are working on weight or volume first. In both examples, we weigh the silicone but the hardener is added on weight or drops. Add hardener by weight per 100 grams silicone use 5 grams hardener.
Add hardener with drops per 100 grams, use silicone least 5 grams hardener. 15 drops is ± 1ml, so 100 grams you need 75 drops.
What you need:
- Liquid silicone (A-component) & hardener (B-component)
- Measuring cup + plastic spoon to mix
- Plasticine clay to seal seams
- Double-sided tape & just wide tape
- Large plate
- Kitchen scale
It is important to have a solid flat surface, a flat plate is a good solution. Then fix the object of what you want to make a mold with a piece of double sided tape and fix it in the middle of the plate (what later the bottom is have to be fixed on the board). Grab a placemat or another thick flexible plastic sheet and turn it around to the object with a 3mm space around the object. Then slice across the seam of the placemat adhesive tape so the palcemat is closed. To be sure tape also on the outside.
Make sure that the silicone does not come in contact with other materials, there is a risk that this can slow or even stop harding the silicone. So no tape, paper, cardboard etc. on the place whare the silicone is!
If your object is porous (such as concrete, plaster, etc.) then the silicone will suck in the pores of your object. The result is that the object gets stuck and can break if you take it out. With Polyvinyl alcohol you can make a thin protective layer (2 to 3 layers are needed) that prevents this.
Another big advantage of polyvinyl alcohol is that you can make a protective layer around the original. Liquid silicone that comes into contact with other materials can react through a chemical reaction so that the liquid silicone will not harden.
Make a roll of plasticine clay like bake bread and create a circle of the size of the placemat. The plasticine clay will not hard and not tear, the silicone can not came out the placemat. The clay can be reused after making the mould. Place the placemat on the plate around the subject and then the clay on the outside of the placemat like a wall. With plasticine you seal the bottom against leaking. Please note that the clay does not come into contact with the silicone because you run the risk that it will not cure!
Place the measuring cup on the scale and press tara. Now you have to gues howmuch silicone you need to make the mold. Put enough of part A into the measuring cup and weigh. Then its time for the hardener with a maximum of 2%. So, at 100 grams Liquid silicone rubber must be used 2 ml hardener, these are 20 drops. Stir well and then pour it over the object and let it dry for at least 24 hours. After this the mold can be removed from the plate, and the mold is ready for use. Keep in mind that its not allowed to make a copy of everything!