One-piece Plaster Waste Mould
Wood frame coated in shellac to seal the board with a light wax coating over the top. Use Vaseline to coat so removal is easier.
First coat -
- Use acrylic or food colouring to colour the first layer of plaster (this will allow you to know you're close to the object cast.)
- Sprinkle plaster into water until it forms little peaks
- Mix to get rid of lumps
- Dribble over the surface to avoid losing detail
- Avoid air bubbles by blowing on the surface or tapping
- Cover enough so the colouration of the clay can no longer be seen
- Let this set slightly before applying the second coat
Second coat -
- Mix up the same plaster but without the colouring
- Cover building it up over the parts that stick out further
- Use a mallet and chisel (an old one so that it doesn't ruin the cast)
- Work from the outside in
- Soak in warm water to soften the soap
- Break away the layers
Two-piece Plaster Waste Mould
- Use brass shim/fencing to divide the object being casted building a wall half way
- Overlap the shim and tape it together so that none of the plaster can leak through
- Cover with fine casting plaster like with the one-piece mould using a spatula to cover the ear
- Repeat with the same plaster without the colouring
- Create a thick flat edge at the top, so you’re able to clamp them together, with the plaster once its dried out and a bit thicker
- Scrape back to find shim edge so you can prise it apart
Creating a positive plaster cast from a negative mould
- Soak the plaster mould
- Coat in soap that’s mixed with boiling water so its runny
- Get rid of surface water with tissue
- It leaves a fine film of soap which acts as release between the plaster and mould.
- Stipple excess off.
- Use Crystacal plaster (harder)
- Mix the plaster as before with cold water (may need more plaster to water)
- Apply with a brush to get surface details
- Tap to get rid of bubbles
- Layer scrim onto wet plaster
- Cover scrim with plaster
- Cover with more scrim
- Cover with plaster
- Tidy edges
- Leave overnight (good 12hrs)
Block Mould (many uses)
- This is a two-part silicone mould and needs more accurate measurement than the plaster moulds
- Use 100g of Part A (silicone) and 10% Part B (fast silicone catalyst) so 10g
- Fold part B into part A and then give it a good whisk (this mix is workable for about an hour)
- Pour it into the piece
- Coat the object making sure to get into all the creases
- Mix in a tiny amount of thixotropic to make a more viscous consistency to add to vertical surfaces
