ABL (STEVENS) Resin & Glass
LATEX RUBBER MOULD-MAKING TECHNIQUES

  LATEX LIQUID RUBBER.
Pre-vulcanised emulsion, which will air, dry on the surface of a master pattern to form a highly flexible thin rubber skin.
Extremely versatile this material is widely used in such diverse fields as the manufacture of moulds for garden ornaments to the production of theatrical masks.
Latex is easy to use, is relatively strong, and will give good definition and accuracy of reproduction.

MOULD MAKING.
When considering making a Latex mould a suitable master must be either acquired or created, choice of materials is quite important.

PLASTER OF PARIS.
Probably the most suitable material as the porosity of the plaster draws moisture from the Latex causing it to thicken.

CLAY MASTERS.
Are suitable but should be allowed to dry out or be once fired before dipping in Latex.

WOOD MASTERS.
Experimental work has shown that moulds can be made on wood masters, which must have a smooth surface and be of a porous nature. The dipping and curing is the same as for plaster and clay.

NON-POROUS MASTERS.
For these types of masters the "Paint On" method will be necessary. Some metals react with Latex resulting in weak moulds.

PLASTICENE MASTERS.
Plasticene masters can be used with Latex but may result in a reduced mould life.

Two mould-making techniques are used, the "Dipping" method or the "Paint On" method.

DIPPING.
This is best carried out with porous masters, as the porosity draws moisture from the Latex, thus causing it to thicken on the surface. However, as the moisture enters, it replaces the air already there, thus forcing air bubbles to form in the Latex. To overcome this, re-dip for a few seconds, remove from the Latex and with a brush, stick, or palette knife, burst the bubbles as they form and spread the Latex over the surface.
As this is being done the Latex will quickly turn to a paste, which will prevent the release of further air, re-dip in the Latex and leave for 15-20 minutes, remove and allow any surplus to drip, off; a mould thick enough to be used should have formed.
The Latex should be touch-dry in ten minutes at normal room temperature (20°C), turning from white to a semi-transparent creamy yellow colour, and ready to peel from the master in 2-3 hours.
Drying can be speeded up, using gentle heat up to about 70° - 75° C.
Before attempting to peel the mould from the master, apply talc or washing up liquid over the surface to prevent it sticking to itself when it is peeled.
If the master is dipped for a longer period a thicker coating will be obtained, needing a longer drying time.
In the event of an over-thin mould being made with the first dip, thickness can be increased by re-dipping as soon as possible but within about 12 hours to ensure the Latex bonding to itself.
Best results are obtained by trying to get the correct thickness of Latex during the initial dip.

PAINT ON.
Paint a number of layers of Latex with a soft brush allowing a part cure at normal room temperature (20°C) before applying the next layer.
If the master is non-porous the latex will tend to "run" so only very thin layers can be applied, keep repeating the process until a skin of sufficient thickness has been built up; for small pieces 7 or 8 layers may be necessary, high spots can be given extra layers.
If the master shape is warmed in an oven before the initial layers are applied a thicker skin will form and subsequent painting will give a better-finished mould.

LATEX THICKENER,
An optional extra that can be added to the Latex if required.
It is particularly useful when painting on non-porous surfaces but can be used on all surfaces and does allow you to build up the thickness of your mould much quicker.
By adding enough thickener to make the Latex similar in consistency to emulsion paint, it can be painted on any surface, porous or not, without running.
To avoid air bubbles, care must be taken to brush the thickened Latex on in thin layers, although after the initial coat has been painted on, it is possible to dip, either in the thickened or the original Latex, in the normal way.
While the addition of thickener at the correct rate will not reduce the strength of the cured Latex or have any adverse effect on the finished castings, excessive use will produce a very rigid brittle mould.
The thickened Latex can be used to take moulds from non-porous vertical surfaces, e.g. wood and stone carvings on walls etc. later supported by a Plaster of Paris or glassfibre case mould, before removing from the original.
As a guide about one drop of the Thickener will thicken 1 gram of Latex so that it can be painted on easily. This amount should be varied to give the best results on any particular job.
If your latex mould is of a large size and liable to distort when used then a support case/jacket will be needed.
This is usually made of either plaster or glassfibre.
No release agent is required when using either of these materials with latex
.

IMPORTANT NOTE: UP TO 10% SHRINKAGE MAY OCCUR USING LATEX PRODUCTS.
These notes are given in good faith for general guidance purposes only and since operating conditions, methods and application techniques are beyond our control, we cannot accept liability for any losses however they may occur.

ABL (STEVENS) Resin & Glass, 4 Millbuck Way, Springvale Ind Est, Sandbach, Cheshire, CW11 3HT
Tel/Fax: 01270 766685    Website: www.resin-supplies.co.uk   Email: enquiries@resin-supplies.co.uk