What kind of rubbers can I use for Mould-making?

This manual will review five of the most widely used mould making materials: latex, alginates, polyurethanes, vinyl hot melts and silicones. Each has advantages and disadvantages. No one material will do everything.

Latex is possibly the most widely used material, mainly because of its comparatively low cost and elasticity. It is capable of making a strong, thin walled mould, ideally suited for one piece “skin” or “glove” moulds

Because as many as 10 to 20 coats must be brushed on to give the mould a workable thickness, with time allowed between each coat to enable the latex to cure or “dry”, making the mould is very slow and time consuming.

In addition latex must be brushed on, dipped or sprayed, it cannot be poured to make a mould. The thin walled nature of the finished latex mould makes a back-up mould a necessity to support the latex and help it to retain its shape when casting.

As shrinkage is also a problem, latex cannot be used to make moulds where dimensional accuracy is a requirement.

Aldax Moulds sell their latex in three grades, #70 which is a thin brush or spray on latex which is used for the first 3 or 4 coats to retain detail, #72 which is a thickened latex used for building up coat thickness and #74 which is a filled latex for use on vertical surfaces.

Our latex can we purchased from our online ebay store by clicking here.

“Hot-melt” (Polyvinyl chloride) is not cheap to buy. However vinyl moulds are cost effective in that they can be re-melted and the material used again.

Vinyl is hazardous and disagreeable to use because of the high temperatures required to melt the material. The high temperature in turn restricts the model materials that can be used with vinyl to make moulds and has fallen from general use.

Silicone rubbers make high quality moulds for casting resins and foams, but the material is very expensive. Silicone is the material of choice for polyurethane plastics and low temperature metals.

It is easy to use, dimensionally accurate and without the moisture problems of polyurethane.

Aldax Moulds have a general purpose silicone rubber CraftSil 750 which we have found has been suitable for over 90% of our customers requirements. View this item on our ebay store by clicking here.

Alginates are mainly used when time is a critical factor or for body casting, as they are completely safe for body contact. They set up in minutes to a rubbery type of gel when mixed with water and give excellent impressions.

Due to the fact that they dry out quite rapidly they must be cast almost immediately after demoulding. Plaster or wax are mostly used in this type of mould.

Click here to view our Minit Mold Alginate.

Polyurethanes are rapidly becoming the mouldmaking material of choice. They are much cheaper than silicones while performing much the same functions. They come in 2 part systems that are easy to weigh and mix due to their fluidity. They can be used for pouring practically any type of cementicious or plaster material, casting resins or foams.

Along with most of these materials they have a limited shelf life and are very “moisture Conscious” however from the point of view of ease of use and economy they have become the preferred mould making material.

The feature of polyurethanes that attracted us most was the long life of the moulds. We used polyurethane exclusively for making of plaster ceramic master case moulds. Unlike latex which under heavy use has a 12 month life, our polyurethane moulds are still producing perfect moulds after 15 years.

While there have been hundreds of different types of polyurethanes developed for specific industry usage, tomorrow the chemists tell use there will be thousands, due to the versatility of polyurethanes from flexible rubbers through foams to hard plastics.

For purchasing information, send us an email to aldax@bigpond.com.au