Latex – How does it work?

The Kwik-Mold Latex series provide the mould maker with all the viscosities of latex needed to make moulds by dipping, brushing and a very thick form for applying to vertical surfaces or for rapid build-up of flat back moulds – #74.

Kwik-Mold 70 is a one-part, dipping or brushing latex. It is a 60% dispersion of natural latex that vulcanizes at room temperatures. It has a strong odour of ammonia and should be used in well-ventilated areas.

We use Kwik-Mold 70 for the first 3 to 5 coats to be brushed on models with a lot of detail, to ensure that we retain maximum detail in the mould with this un-thickened natural latex. Brush with a stipple action to lay an even coat and eliminate as many air bubbles as possible.

Kwik-Mold 72 is a thickened form of latex designed for use on all subsequent brush coats, after using Kwik-Mold 70 for the primary coats. It provides an ideal way of building up coat thickness as rapidly as possible, while still retaining maximum strength in the finished rubber mould.

Kwik-Mold 74 is a filled form of latex for use on vertical surfaces where its thixotropic character enables rapid application of rubber that will stay where you put it or for rapid build-up of final coats of flat back plaque moulds.

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. However the polyurethanes are catching up fast and are in use for concrete press moulds, where a final thickness can be brushed on in half a day.

How to seal your model

Wherever possible we endeavor to make our 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 the latex Mould

Latex makes the thinnest, most elastic and strongest mould of any type of mould making rubber. It can be polled 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.

To assist beginners, we have produced a kit based on our methods here at the factory for making a plaque mould. Click here for more information