How do I use Jesmonite?

Jesmonite is supplied in two parts, a liquid and a powder, these are mixed at a ratio of between 2-3 parts powder to 1 part liquid. Digital scales are not necessary to measure this material.

1. Measure out an adequate amount of powder first and add the acrylic liquid at a ratio to suit your work. Remember, the more of the acrylic liquid produces a runnier liquid. Check with your technician what viscosity suits your work best before starting.

2. Once combined the powder and liquid begin to react quickly so do not delay mixing and application. I find using an electric whisk or similar for about 1-2 minutes is enough to ensure all the lumps of powder are gone and it is a smooth texture before applying.

3. The mixture can be applied by brush as a plastic coating or in conjunction with fibre-glass. It can also be poured as a solid or a hollow slip casting.

Tip: The more powder you add the thicker the material becomes. Handy for filling the bits you’ve missed. Also adding more liquid will thin the material, making it ideal for casting highly detailed surfaces.

4. After around 15-30 minutes the surface can be worked like plaster, which makes it a great choice for fabricating complicated one-off shapes quickly and easily. Over the next 24-48 hours, the jesmonite will gradually harden into a tough plastic like material that can be cut, shaped, sanded and painted.

What is Jesmonite?

Although it has been around since the 80’s Jesmonite is a relatively little known material despite the fact it remains one of the only water-based resins around today. Jesmonite is made up of two components, a liquid acrylic compound that binds a gypsum powder (not unlike that used for plaster casting). The resulting mixture acts much like plaster for 24 hours or so then hardens to acrylic-like properties.

It is ideal for covering large foam sculptures by itself or together with fibre-glass matting to add extra strength.

Because it is a water based compound, all the protective equipment necessary when working with G.P resin and fibre-glass is not required. Although a dust mask and goggles are essential when mixing any powder or liquid.

There are several types of Jesmonite already available and new developments released in 2008 included the introduction of metal finishes for cold metal casting

Because it is a water-based resin, it is also ideal for coating polystyrene sculptures and foam core furniture designs with a durable, exterior shell, which can be sanded painted or upholstered to meet the users needs.

On its own it is very strong, it’s even weather proof, much like the properties of plastic, yet when combined with fibre-glass matting it becomes extremely strong and highly durable. It is also impact and flame resistant.

It is very popular when making large or load bearing structures particularly when used with polystyrene block sculpture as a core. This keeps the weight to a minimum whilst not compromising on structural strength.

It is also suitable for making children’s toys and interactive sculptures where conventional resin/fibre glass usage would not be suitable.

It is also easier and less harmful to sand and finish making it quicker and safer to achieve a professional looking surface.

 ‘Mind-control’ skull for The Gadget Show. AC100 over a foam core

Currently there are several types of Jesmonite:

AC100 is a good general purpose resin suitable for outdoor applications and is very durable.

AC200 and AC300 which are both designed primarily for indoor use.

AC730 which is a cement substitute essentially suitable for water features and submersed casting as well as replicating stone finishes.

  Phone- glass reinforced AC100 resin, steel/foam core
           Polystyrene foam commonly used for sculpting
First layer of stitched glass fibre reinforcement with Jesmonite
  Taking shape after several layers of glass fibre and Jesmonite
           Metal reinforced, foam core and Jesmonite light
    Blue foam core and AC100
   PS foam painted with AC100


Most Jesmonite types costs around £8.00 per kilo

Expect to pay £60.00 or so for 20 kilos of AC100.

This cost varies depending on how much you buy.

Bulk buy’s are usually cheapest.

 Spray painted, stitched glass-reinforced   
        AC100 over sculpted foam core
Primed, AC100 over sculpted foam core