What is a Single Part Open Mould?


This is one of the simplest form of mould making. This method is not suitable for larger castings or shapes with large undercuts. We can use a number of different materials to make this kind of mould, such as latex, polyurethane rubber or silicone. Due to the nature of this type of mould we must always use a flexible material to make the mould. This allows us to flex the mould to remove the castings easily.


The advantage of this type of mould-making is that casting material can be applied in stages allowing for multiple layering of resin slip casting and embedding or encapsulation. It also allows moisture in water soluble casting materials, such as plaster, concrete and cement, to evaporate more readily.



 

Single Part, Open Mould

 

How do I make a Single part open mould?



To demonstrate how to make an open mould, I have documented a real example below.


1. Construction of a container or vessel for your object to be cast is the first step when making this type of mould. It can be made simply by using either clay, MDF, wood, vinyl or anything else available that has adequate depth and size, like plastic cups or cut off bottles.

However, I prefer to use a combination. Stick the master to a rigid base (MDF) using hot glue or other suitable non-permanent adhesives. The vessel walls can then be constructed out of thin metal sheet, clay, MDF, or anything else that will hold the weight of the silicone to be poured without leaking.



Tip: before measuring out your mould making material it is helpful to pour water into the vessel first to work out how much you will need bring the mould to the required level (usually 10-15mm covering above your object)

Remember to place your object to be cast in the vessel with the water in order to displace the excess water, we then carefully pour out and measure the volume (not weight) of water remaining. This is a good way to ensure only minimal wastage occurs when mixing the silicone. Of course this method is only possible if both object and vessel are compatible with water, so check with your technician first.


2. Next, mix as much silicone as you have estimated will be needed to fill the vessel, baring in mind that we will need 10 - 15mm extra, above the height of the master.


3. When pouring the silicone always pour into the lowest point of the vessel containing the master.


4. Once the silicone is set, remove the vessel walls and pull the silicone from the board (this takes a bit of brute force sometimes). Remove the master and you are ready to begin casting. Simple.

   

Single part, open and split mould-making

   

Single part, open mould-making and clear resin casting’s