The experiments so far trying to cast a block of investment plaster have been varied and I am determined to get this right. So the mix recipe is working, I am getting a smooth plaster, but when casting I need to consider the horizontal expansion especially when using rubber buckets.
Sometimes the answer can appear where you least expect it. I was taking out some rubbish to the large bin outside. The bin is shared between all the studios at the Ferrers Centre and it was almost overflowing being bin day. Sticking out the top was a collection of foam sheets, one of the studios has a Upholsterer and they must have stripped an old seat and discard the foam to replace it with new foam. Thats when I had my eureka moment, the problem with my last experiment was choosing polystyrene chips to line my bucket, but they vibrated out of the bucket, but foam would not vibrate out. I took the foam.
New plan
Step 1 - Line the larger bucket with sheets of upholstery foam, then line with polythene sheeting
Step 2 - Pour in the plaster mix, vibrate and leave to set
I have now lined my bucket with the sheets of foam and lined it with plastic, easy so far. I have mixed up a batch of plaster and poured it into the prepared bucket and placed it on the vibrating plate.
Success! the vibrating does not dislodge the foam and it is working so far. Just go to wait 2 hours until its set to see if my plan has worked.
Fingers crossed