Gypsum plaster, clean bucket, water, spirit level, Vaseline/petroleum jelly, 12 mm thickness wooden dowel, PVA glue (or similar strong water based craft glue), two slim glass louvre window panes (2 or 4, I used two for this project) or smooth melamine wood cut to size, duct tape/packaging tape and you obviously need a finished latex mould with positive objects still contained inside the mould :)
|Old louvre window panes, smooth side up, are ideal to use as latex mould bases.|
To make my latex mould, I secured my positive objects first on a recycled window louvre, flat side up. Fifteen layers of latex later, the mould is ready for a plaster 'mother' mould or backing mould. Applying fifteen layers of latex means that your latex mould will last longer and your mould will be the strongest it can possibly be.
|Fifteen layers of latex is recommended to ensure strength and durability of your mould.|
1. I applied petroleum jelly/Vaseline, to the dry latex mould above, with the positive objects still enclosed within the latex mould :)
2. I measured the highest point of my latex mould and cut six identical pieces of wooden dowel to act as levellers for my finished plaster mould. I left a gap of 2 cm above the height of the highest latex mould so that the finished plaster mould will support it well.
|Ensure your glass pane and wooden dowel pieces are level. Glue the dowel pieces down with the loose top glass pane acting as a weight on top.|
3. I glued down the wooden dowel pieces to the latex mould and waited around 30 minutes for glue to dry. Do not glue the glass pane down!!! Keep the glass pane on top to help set the wooden dowel pieces to the latex. Once the dowels are glued down, remove the louvre pane.
4. I then made a supporting frame around the latex mould, but I only used glass louvres on the two longest sides of the mould to shape the rectangular plaster mould, because I just needed a flat bottom to support the latex mould, with the dowels used as a guide to finished height level of the plaster. If you wanted to, you could build a wooden, or a cardboard or linoleum or metal frame around the outside edges of the louvre to support the plaster mould as it is poured. I just used two louvres to make a frame, butting two glass window panes opposite each other, on the longer sides of the latex mould. At this point you can tape around them using duct tape or ordinary packaging tape. The tape will enclose the two shortest open ends of the mould.
5. Apply petroleum jelly/Vaseline to the glass louvre panes (optional but a good idea).
6. Prepare your plaster. Fill your container with water. Add dry plaster mix at a ratio of roughly equal parts water to powder. Once the plaster is visible over the water line, start to mix with a spoon or I use my hand/s so I can squish out any lumps and feel the thickness and temperature of the plaster. The plaster will feel warm once it is thickening and the texture should be as thick as a soft 'butter' type consistency. Leave it a bit on the soft side, as once it starts to harden quickly if it is too thick, will not leave any room for smoothing it down once it is applied to the mould.
7. Pour your plaster onto your latex mould and fill completely up to the top of the wooden dowels. Once your mould is filled over by plaster, place your glass louvre pane firmly on top of the plaster and press down firmly on top of the dowels, to ensure it is level (This is optional but good for producing a very flat plaster surface). Try to keep the shortest sides of the mould covered with plaster too. What we want to end up with is a rectangular plaster box shape with a perfectly flat bottom to support our latex mould, once turned over right side up.
7. Once finished, you can remove the glass pane once the plaster has set. The glass should not stick to the plaster. Your plaster mould underneath the glass window pane is the finished bottom side of our mould. Once dry, flip the finished mould over and leave the latex mould enclosed in the plaster until it is completely set.
Warning: Mixing plaster with your hands, squishing it between your fingers then sculpting with it can be seriously fun.