What Is Jesmonite®? A Beginner’s Guide to Jesmonite AC100

Jesmonite® is a registered trademark covering a range of two-component composite systems used in art, design, decorative objects and architectural applications.

In everyday use, the word Jesmonite is often used as if it were a generic name for mineral casting materials, but Jesmonite® is a specific brand with several different product systems.

One of the most popular systems for creative projects is Jesmonite® AC100. It is a water-based, two-component acrylic polymer and mineral-base composite system suitable for decorative casting, interior objects, mould work and a wide range of surface effects.

Jesmonite® AC100 can be used to make:

• coasters;
• decorative bowls;
• candle holders;
• plant pots;
• figurines;
• jewellery;
• wall decorations;
• sculptural objects;
• terrazzo- and marble-effect pieces;
• other decorative cast objects.

AC100 captures fine mould detail well, can be pigmented, sanded and finished with suitable sealers or protective coatings.

What Is Jesmonite® AC100 Made Of?

Jesmonite® AC100 consists of two components:

• Jesmonite® AC100 Liquid – a water-based acrylic liquid;
• Jesmonite® Base – a mineral powder component.

The standard AC100 mixing ratio is:

2.5 parts Base : 1 part Liquid by weight.

For example:

• 250 g Base + 100 g Liquid = 350 g mixed material;
• 500 g Base + 200 g Liquid = 700 g mixed material;
• 1,000 g Base + 400 g Liquid = 1,400 g mixed material.

The components should be weighed accurately using scales, rather than measured by volume or estimated by eye.

An incorrect mixing ratio may affect setting, strength and the final properties of the cast object.

How Is Jesmonite® Different from Epoxy Resin?

Although Jesmonite® is sometimes described as an “eco resin” or water-based resin, it should not be treated as the same type of material as epoxy resin.

Jesmonite® AC100 is:

• water-based;
• a two-component system;
• solvent-free;
• low in VOCs;
• based on an acrylic polymer and mineral component;
• a relatively fast-setting casting material.

Once cured, AC100 usually has a matt, mineral-like surface, making it particularly suitable for stone, concrete, marble and terrazzo-style finishes.

How to Prepare Jesmonite® AC100

1. Weigh the Components Accurately

Use digital scales.

First weigh the required amount of AC100 Liquid, then add the correct amount of Base, maintaining the 2.5 : 1 ratio.

Incorrect proportions are one of the most common beginner mistakes.

2. Add Pigment if Required

For an even colour, Jesmonite® pigment can first be mixed thoroughly into the Liquid component before the Base powder is added.

The maximum recommended amount of Jesmonite® pigment is 2% of the total mixed weight.

For example, 1 kg of mixed material should contain no more than approximately 20 g of pigment.

In many cases, significantly less is enough to achieve a strong colour.

Too much pigment may affect:

• setting;
• consistency;
• mechanical properties;
• the finished surface.

3. Mix the Liquid and Base

Small quantities can be mixed by hand, while larger batches are easier to mix consistently using a Jesmonite® high-shear mixing blade.

When mixing:

• make sure no dry powder remains;
• scrape the sides and bottom of the mixing container;
• aim for a smooth and uniform consistency.

Mixing very slowly is not a strict requirement – the key is to use an appropriate mixing method while avoiding unnecessary air incorporation.

How to Reduce Air Bubbles

Small surface pinholes are one of the most common problems when casting Jesmonite®.

Several techniques can help reduce them.

Apply a Thin First Coat

If the mould contains fine details, brush a thin 1–2 mm layer of Jesmonite® onto the mould surface before filling it completely.

This helps the material reach small details and reduces the chance of visible surface bubbles.

Gently Tap or Vibrate the Mould

After pouring:

• tap the mould gently against the work surface;
• lightly vibrate or move the sides;
• for larger-scale work, a vibrating table can be used.

This encourages trapped air to rise.

Do Silicone Moulds Need Release Agent?

Usually not.

High-quality silicone moulds are popular for Jesmonite® because they are flexible, reproduce fine detail and usually allow the cast piece to be removed easily.

Release agents are more commonly required with rigid mould materials, such as:

• plaster;
• Jesmonite®;
• fibreglass;
• metal;
• wood;
• glass.

Do not automatically apply mould release to every silicone mould. Follow the recommendations for the specific mould material.

How Long Does Jesmonite® AC100 Take to Set?

Jesmonite® AC100 is a relatively fast-setting material.

At around 18°C and without Retarder, the initial set begins after approximately 15–20 minutes.

However, the time before a cast can safely be removed from the mould depends on:

• ambient temperature;
• thickness of the object;
• mould size;
• additives;
• working conditions.

In practice, demoulding may take anywhere from approximately 30 minutes to several hours.

Warmer conditions generally accelerate setting, while cooler conditions slow it down.

When Can Jesmonite® Be Sanded?

Being able to remove the object from the mould does not mean that all moisture has left the material.

Jesmonite® AC100 is water-based and continues to dry and cure after demoulding.

Before:

• sanding;
• sealing;
• applying a protective coating;

it is advisable to allow the object to dry for at least 24 hours, while some pieces may benefit from 24–48 hours.

How to Sand Jesmonite® Objects

Fully dried AC100 can be sanded.

Start with an abrasive appropriate for the surface and gradually move to finer grits as required.

Sanding produces mineral dust, so:

• work in a well-ventilated area;
• avoid inhaling dust;
• use suitable respiratory protection where appropriate;
• remove dust thoroughly before finishing the object.

Sanding is especially popular for terrazzo-effect Jesmonite®, where removing the top surface reveals coloured chips embedded in the material.

Does Jesmonite® AC100 Need Sealing?

This depends on the intended use of the object.

AC100 has a naturally porous surface, so a suitable sealer may help reduce:

• water absorption;
• staining;
• absorption of dirt.

Sealing can be particularly useful for:

• coasters;
• plant-pot saucers;
• bathroom accessories;
• frequently handled decorative objects;
• pieces exposed to moisture.

For outdoor use, an appropriate sealing or paint system is recommended.

Jesmonite® AC100 should not automatically be considered fully waterproof simply because it has cured.

Is Jesmonite® AC100 Food-Safe?

Jesmonite® materials should not automatically be assumed to be suitable for direct food contact.

Therefore, bowls, trays and plates made from Jesmonite® should not be marketed as food-contact products unless the finished item and its coating system have been separately assessed for that use.

A decorative bowl is not the same as a food-serving bowl.

7 Common Mistakes When Working with Jesmonite® AC100

1. Estimating the Mixing Ratio by Eye

AC100 must be mixed by weight, using the 2.5 : 1 Base-to-Liquid ratio.

What to do:
Use accurate digital scales.

2. Adding Too Much Pigment

More pigment does not necessarily produce a better or richer colour.

What to do:
Do not exceed 2% of the total mixed weight, and begin with much less whenever possible.

3. Waiting Too Long Before Pouring

Mixed AC100 begins to set relatively quickly.

What to do:
Prepare the mould, pigments and all tools before mixing the components.

4. Trapping Too Much Air

Poor mixing or pouring technique can introduce visible air bubbles.

What to do:
Mix thoroughly, apply a thin face coat to detailed moulds and gently vibrate the mould after pouring.

5. Using Release Agent on Every Mould

Release agent is not always necessary with good-quality silicone moulds.

What to do:
Consider the specific mould material and follow its manufacturer’s instructions.

6. Sanding Too Early

A piece may be ready to demould but still contain moisture.

What to do:
Allow it to dry for around 24 hours before sanding or sealing.

7. Assuming Jesmonite® Is Automatically Waterproof

AC100 can be used for many decorative objects, but surface performance depends on the final finish and intended use.

What to do:
If the object will be exposed to water, staining or outdoor conditions, select a suitable protective coating.

Jesmonite® AC100, AC84 or AC730 – What Is the Difference?

Jesmonite® is not just one material.

Jesmonite® AC100

A water-based acrylic polymer and mineral-base system that is particularly popular for decorative casting.

Suitable for:

• coasters;
• bowls;
• candle holders;
• figurines;
• terrazzo and marble effects;
• interior décor.

Jesmonite® AC84

An acrylic polymer-modified cement-based system.

It is suitable for decorative casting where a more cementitious character and different performance profile are required than with AC100.

Jesmonite® AC730

An acrylic polymer-modified cementitious micro-concrete composite, designed for more demanding decorative and architectural applications, including outdoor use.

For this reason, it is better to choose a specific Jesmonite® system according to the intended use, rather than simply buying “Jesmonite”.

At Magicminiature.lt you can find  Jesmonite® AC100, AC84 and AC730 systems, pigments and accessories.

Is Jesmonite® Suitable for Beginners?

Jesmonite® AC100 is one of the most accessible systems for getting started with decorative casting.

The basic process is straightforward: accurately weigh two components, mix them, add pigment if required and pour the material into a mould.

For a first project, consider using:

1. a simple silicone mould;
2. a small AC100 kit;
3. one or two Jesmonite® pigments;
4. accurate digital scales;
5. a mixing container and spatula;
6. a simple project such as a coaster or small decorative pot.

The most important points are to weigh accurately, prepare everything before mixing and avoid sanding or sealing immediately after demoulding.

Once you are comfortable with basic casting, you can experiment with marbling, terrazzo, layering, metallic powders, glass granules and other decorative effects.