Liquid Latex
Latex - Liquid form for masks, moulds, casts, make-up and special effects.
Latex makes the thinnest, most elastic and strongest mould of any type of mould making rubber. It can be pulled over
relatively large undercuts when releasing the model without tearing.
The strongest moulds are made by brushing on thin layers of latex. The number of coats can vary from 8 to 20 or more
depending on the size and purpose of the mould. A simple mould of a chess set piece about 15cm high would normally take
about 8 to 10 coats, each coat applied, then let to dry in a warm area until the white colour disappears before applying the
next coat. About an hour or so between coats would be normal. To speed things up you can use a fan driven radiator or
hair dryer to dry the water in the latex. The colour changes to an amber rubber colour.
Latex cannot be poured or applied in thick sections, it will not cure. Your mould when completed will be quite thin and if
above say 15cm in height will require a back-up mould to support its shape when casting.
Latex uses
Ideal for casting plaster, concrete but can also be used for limited casting of some resins. As a white brush-on liquid, after
multiple applications it builds up to a mould thickness of 1 to 3mm that air vulcanizes to a light amber colour. This forms a
very tough, blanket mould with great elasticity.
Latex has a better tear strength than all synthetic rubbers and is preferred by the concrete and plaster shop industry when
used as a sock mould or one that peels off a casting, just like you pull a sock off your foot.
How to seal your model
Wherever possible make your models in plaster. Plaster is porous and does not need a sealer or release agent. Also latex
peels off the model quite easily.
This does not apply to all porous items particularly wood, which due to its fibrous nature can cause problems unless you
seal the surface. You can seal with several coats if paste wax or by spraying with lacquer, shellac followed by a coat of
release agent.
Wax, glazed ceramics or glass do not need sealing or application of a release agent. Avoid petroleum-based products,
solvents and oils as they are not compatible with latex and will cause its degradation over time. If in doubt test a small area
to see if it releases satisfactorily.
Making a Mould Using Brush Method.
Latex may be used to make moulds from masters (originals) made from various materials such as plaster, clay, glass and
concrete. Ensure the masters are clean, dry and free of grease or oil. Except for plaster models, masters may be washed in
a solution of dishwashing liquid and water and dried before latex application.
Fasten the master to a firm non-porous substrate so that the entire piece can be moved without handling the coated areas.
The latex compound may be used as an adhesive by pouring a small quantity onto the support, positioning the model and
allowing the assembly to dry.
Brushes used to apply moulding latex should be rinsed in a solution of soap and water both before and after use. This aids
cleaning of the applicators and prolongs their use.
When applying brush latex, care must be taken to eliminate all air bubbles in the first coat. This will ensure that the detail is
accurately reproduced. If a thinner viscosity is required for the first coat, the brush latex may be diluted with a small
amount of distilled water. Brush from the top of the model to the bottom and continue out from the base to a distance of
approximately 4 cm on the supporting substrate. Apply the overlap for every coat of latex, not just the first. When dry the
excess film provides a useful handle in casting operations.
The first coat should be dried at room temperature (23 – 25 deg C) in order to minimise lifting from the master. Once the
first coat is completely dry to touch subsequent coats may be applied. Drying between coats may be carried out at room
temperature. To speed up the process the drying temperature can be increased up to a maximum of 50 deg C either in an
oven or by fan heater. If no heat is available, directing a current of air across the surface of the model at room temperature
will speed the drying.
Do not use excessive heat as this may:
• Promote shrinkage
• Cause cracking
• Trap moisture in the film
• Lead to low tensile strength
• Cause delamination between layers
For models with a relatively large surface area, the following application may be considered. Apply the first coat of latex as
described. When this is dry follow with a layer in a checkerboard pattern. Once the checkerboard application dries follow
with an entire coating. Continue alternating between the full coat and the checkerboard coat until desired thickness is
achieved. This technique helps to reduce the tendency to shrink and keeps the dimensions of the finished mould very close
to those of the original.
Reinforcement of the latex
This can be achieved by applying strips of cheesecloth, burlap or a similar open weave cotton fabric
to the mould after four applications have been made. The fabric should be cut into narrow strips and applied to a fresh coat
of latex. After this has dried a further two or three coats of latex should be applied over the fabric. Do not apply
reinforcement to areas which will need to stretch to facilitate the item's release from the mold.
The recommended number of latex coats for a model approximately 15 cm high is five to six. For models 30 cm high or
larger, ten to twelve coats may be required.
Once the final coat of latex is applied the mould should dry for 24 – 72 hours at room temperature to cure. To improve the
tensile strength dry for 13 hrs at 50 – 60 deg C.
Peel off the mould. The latex should be very durable and can be peeled right back inside-out. Then just pop it back to it's
original shape.
Build a support stand for the mould. For most items it is best to support the mould just under the flange so that it is
suspended. Larger items may require extra enforcement such as a wooden box to keep it in the proper shape when filled.
Cast your item using any casting medium. Plaster of Paris is probably the easiest and can be painted later. Polyester resin or
similar polymers will reproduce very fine details in your item.
Making a Mould Using Dipping Method.
This needs to be done with a porous master which is simply dipped into the liquid latex. The porosity draws moisture from
the latex causing it to thicken on the surface. Unfortunately, as this happens, air bubbles are formed in the latex. To
overcome this, remove the master from the latex after a few seconds and use an old brush the stipple the surface and
thus burst the bubbles. If you have had to burst some air bubbles you must re-dip immediately. Let the master dry for
approx 15 minutes before re-dipping and allow to touch dry before each re-dip. The number of dips required will depend
on the size of master and master complexity.
Remove the master from the liquid latex and leave it to dry for at least 3 hours before removing the mould as described
later.
Making a Mould Using a Thickening Agent
A thickening agent can be mixed into the latex. This converts the latex into a paste of about the same consistency as
whipped cream; The original
should be firmly positioned on a base-board and the latex pasted on, starting at the bottom and working up preferably applying a thin film all over first, so that visible bubbles can be eliminated - although
this problem can largely be eliminated if an initial coat can be applied using un-thickened latex (either by dipping or
painting). ideal for most large projects. Inevitably, the outer surface of the newly-created mould
will only be as good as the finish that can be given to it with the knife or trowel, etc., although this does not usually
matter. Although thickener stiffens the latex, it does not significantly affect the overall drying time.
Thickener is normally added in the ratio of between 1% and 5%, very gently mixing in a small amount at a time until the
desired consistency is reached. Look in our shop if you require latex thickening agent separately.