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What Mould Rubber to Use?

Molding Silicone, Latex Rubber or Polyurethane Rubber

The three most popular types of mould rubber currently used are latex, silicone and polyurethane. All three types of mould rubber have their uses, advantages and disadvantages and all have to be considered before selecting the correct mould rubber for each project.

COMPARISON OF MOULD MAKING RUBBER
Properties
Latex
Molding Silicone
Polyurethane
Description
One Part Mix
Two Part Mix
Two Part Mix
How to use
Brush on 12 to 20 coats
Pour on
Pour on or Brush on
Cost
Lowest Cost
Highest Cost
Medium Cost
Cure Time
to 1 hour each coat
6-8 hours
24 hour cure
Ease of Use
Time consuming
Harder 2 part mix
Hardest mixing
Mould Type
Glove mould
All types
Block or 2 part

Advantages:
Latex is a low cost mould rubber which usually does not require a release, stretches easily, and cleans up with soap and water
Molding Silicone is extremely versatile, no release agent is required, many different varieties made.
Polyurethane is extremely durable, releases air bubble easily and is made in many degrees of hardness.
Disadvantages:
Latex has very limited life,12 months usually, it takes a long time to make a mould with half to one hour between coats it can take several days to make a mould and due to its flexibility it requires a mother mould to hold the shape during casting.
Molding Silicone is more difficult to mix and usually requires removal of air bubbles with a vacuum. It is the most expensive rubber.
Polyurethane requires release agents, takes 24 hours to cure and is limited in the number of mould types it can be used for.

OUR PERSONAL FACTORY PREFERENCES
Wherever possible we use molding silicone. The extreme ease and speed of use, reliability and easy release qualities makes the price unimportant in our case. The combination of a silicone mould and the use of polyurethane resin as a casting medium opens the door for the production of countless hard plastic items from train and vintage car parts. 8 hours or less for the molding silicone to cure and 10 minutes to produce a white hard plastic figurine in resin.


WHEN DO WE USE THE OTHER RUBBERS
For hobby casting of plaster, latex is still our rubber of choice and articles on how to make latex moulds are available on our website.
We recommend that where you are just starting out and the labour is your own, latex moulds can still be used economically for casting concrete, replacing the moulds on an annual basis. They are used as usual with a fiberglass or plaster back up mould.
For concrete moulds of all types we prefer to use polyurethane. It has outstanding long life characteristics (up to 15 years) and does not need back up moulds.


Aldax CraftSil Mould Making Rubber
Aldax KwikMold Mould making Rubber

 

 
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