So today, we will make a plaster press mould using this silicone mould we have just recently created.
First things first, we need several buckets, one for the plaster, one for mixing (and holding the water in the beginning), a bucket with a spout for pouring into the mould, a bucket full of water, a battery drill and a paint mixer attachment, you can use a whisk, but it isn’t easy to mix such a large amount of plaster, and it doesn’t always necessarily mix perfectly.
We start by measuring out our materials into our buckets; for me, it was 4,400gm of plaster and 3080gm of water (70% water to plaster ratio). Make sure throughout this process that you are wearing a mask, as you can see in the video, it is very dusty and is no good to breathe in.
Next, we add the plaster to the water in the bucket while sifting it through our hands to get an even coverage. Don’t start mixing at this point; get your drill ready, and once you have waited 1-2 min, the water will have soaked into the plaster somewhat, and you can begin mixing.
You should mix the plaster thoroughly making sure not to create a whirlpool in the plaster as it will introduce air bubbles into the mixture which you want to avoid as best as you can.
Then, you pour your plaster into the bucket with the spout and mix again, ensuring you don’t create a whirlpool. Once you have thoroughly mixed the plaster (for me, I mixed it for 5 min on the day, but it will depend on the temperature), you then spray a Windex solution into the silicone mould.
The Windex solution is 1/3 Windex to water in a spray bottle; you spay your mould because silicone is resistant to water, and thus, in a reaction I don’t fully understand, pushes the bubbles in the plaster away from the surface of the mould, giving you a clean mould surface.
You then slowly pour your plaster into the mould off-centre to the main casting surface (or, in this case, the press mould surface) and let the plaster flow over the casting surface, which further reduces the possibility of air bubbles being on the surface of the mould.
Once the mould is filled, spray the top with an alcoholic spray (I use Isopropyl Alcohol). This spray breaks the tension of the surface and helps allow the bubbles to burst.
I would also like to thank @vantiki for his very informative videos on mould-making, so check him out on YouTube!
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