Sunday, 12 February 2017

How To Make a Plaster Support Mould For Latex Moulds

Materials required:

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.
Please note that I have left all of my positive objects still enclosed within my finished latex mould, just as they were when I was making the latex mould. Do not remove them, or your plaster mould will not be effective!!! 


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. 

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. 

Saturday, 28 January 2017

Making A Multi Cavity Silicone Soap Mould

Project: Making a multiple cavity (Egyptian) silicone soap mould.


RTV Silicone/catalyst -  or you could use a Latex rubber moulding compound which I do in my next post.

Bathroom heat lamp globe (sold in supermarkets for under $15) which is used to soften modelling compounds and to provide even heating for the silicone mould once it is finished.

Modelling compounds - Plasticene, heated with the heat lamp for a couple of minutes;
Fimo oven bake clay - the Chinese variety, commonly found on Ebay under 'oven bake clay' or 'polymer clay' (The cheaper the better because the cheaper ones are harder and less pliable).

Cheap thin paintbrush, from a child's set or similar.

Cheap pourable craft glue, from discount stores.

Offcut of a tile, glass sheet or perspex, or anything else with a smooth, flat finish.

Egyptian positive object/s, with flat bottoms. You can use anything else you like to make an embed, as long as the underside is flat. Jewellery pendants, charms and buttons are examples.


First, I secured my Egyptian positive objects to a long piece of perspex offcut using craft grade glue (found in discount stores). I used the cheap paintbrush to brush the glue all over the back of the positive object, with the glue being thicker in the middle. The sheet of perspex then went under the heat lamp for 30 minutes, to set the glue.

Once the objects were glued onto the perspex firmly, I then backfilled any protruding undercuts underneath each positive, using warmed plasticene and poked the warm plasticene around using the non paintbrush end of the paintbrush. The perspex was then placed onto a piece of wood which was levelled using a spirit level. Although it looks like the positive objects are sitting on a wooden base, they are sitting on the clear acrylic perspex. 

Next, I built the mould walls and borders around the perspex base. I used the cheap and nasty 'oven bake clay/polymer clay' which I cut in long strips about 1 cm high. 
 I then used softened plasticene to build a softer wall on top of the polymer clay and filled in any gaps along the bottoms and made sure there were no gaps on the inside or the outside of the mould. I did not bake the 'polymer' clay in the oven for the bottom still needs to be soft enough to adhere to the perspex and plasticene. Using the other end of the paintbrush, I poked and prodded the warm plasticene around until I was happy there were no gaps. Now it is ready for pouring silicone into, to make the mould. 

The positive Egyptian objects adhered to perspex, with the wall of modelling clay and plasticene now complete.

Now with the mould walls secured around the perspex, I poured the silicone into the mould and turned the heat lamp towards the mould once it was finished.

One polymer clay strip on the bottom layer, with softer plasticene moulded onto the upper layer.
Finished silicone multi cavity embed mould
As it is a mild summer evening, I will leave the heat lamp on overnight to ensure the temperature of the silicone constantly stays at around 23 degrees. I can soon smell the familiar smell of the catalyst warming the silicone, which is a good sign. Within 48 hours my mould should be cured and ready to demould.

Thank you for reading my blog about my serious silicone moulding addiction :)