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Choosing WEST SYSTEM hardeners, fillers and additives

Whether you are looking for a hardener that gives a natural wood finish, a filler for fairing or a fire-resistant additive, you will identify here which WEST SYSTEM® product is suitable.

In the following tables, you can compare applications of the full range of WEST SYSTEM hardeners, fillers and additives and decide which is best for your project.

Which hardener do I need?

Hardeners are mixed with epoxy resin. The mixture cures to a high-strength plastic solid at room temperature which can be used to bond a wide range of materials. This table shows the relevant uses and cure speeds of the four WEST SYSTEM hardeners.

Uses Resin/Hardener
Hardener Temperature Range (°C)
Cure Speeds at room temperature
room temp 1
Pot Life 100g
Working Time thin film
Cure to Solid thin film
General bonding, fabric application and barrier coating
room temp 1 1
10-15 min
60-70 min
5-7 hours
General bonding, fabric application and barrier coating
room temp 1 2
20-30 min
90-110 min
9-12 hours
Fabric application and coating for natural wood finish
room temp 1 3
20-30 min
85-110 min
9-12 hours
General Bonding, fabric application and barrier coating
room temp 1 4
50-70 min
200-260 min
20-24 hours

Which filler do I need?

Fillers are used to thicken the basic resin/hardener mixture for specific applications. Each filler possesses a unique set of physical characteristics, but they can be generally categorised as either adhesive (high-density) or fairing (low-density).

Adhesive filler mixtures cure to a strong, hard-to-sand plastic useful in structural applications like bonding, filleting and hardware bonding. Any of the WEST SYSTEM adhesive fillers are suitable for bonding situations.

Fairing filler mixtures cure to light, easily sandable material that is generally used for cosmetic or surface applications like shaping, filling or fairing.

As a rule, it is better to use higher-density fillers when bonding higher-density materials such as hardwoods and metals.

1. Uses
Adhesive fillers
Fairing fillers
2. Applications

3. Desired characteristics
Highest density
Highest strength
Lowest density
Easiest sanding
1. Small GRP repairs
1. Bonding hardware
2. Increased fastener interface and hardware load capability
3. Maximum strength
1. General bonding
2. Join parts with epoxy thickened to create a structural gap filler
3. Strength / gap filling
1. Bonding with fillets
2. Increase joint bonding area and create a structural brace between parts
3. Smoothness / strength
1. Laminating
2. Bond layers of wood strips, veneers, planks, sheets and cores
3. Gap filling / strength
1. Fairing
2. Fill low areas and voids with an easily sanded surface filler/fairing compound
3. Sandability / gap filling

Which additive do I need?

Additives are blended with mixed epoxy. They alter the physical properties of epoxy when used as a coating. Additives can be used to alter the colour, abrasion resistance or moisture resistance of cured epoxy. This table explains which WEST SYSTEM additive is suitable for which common application.

Resin/hardener mixture with an additive
Abrasion Resistance
Apply undercoats of epoxy modified for abrasion resistance or temporary UV resistance.
Fire Resistance
Apply a more fire resistant coating in engine and galley areas.
Moisture Resistance
Apply undercoats of epoxy modified for maximum moisture protection.
Apply as a tough, low-friction coating, or as a bearing surface when thickened with fillers.
Antifouling Primer
Apply epoxy undercoats with increased abrasion resistance and backup antifouling properties.
Pigmented Undercoat
Apply an opaque, coloured epoxy undercoating as a base for painting.

How do I colour epoxy?

To obtain a colour other than white or grey, add powdered pigments (e.g. tempera paint, coloured tile grout or aniline dye) and universal tinting pigment to the epoxy mixture. Acrylic paste pigments can also be used to tint the mixture, as long as they are specified for use with polyester or epoxy resin. 423 Graphite Powder will colour the epoxy black or impart darker shades to colours.

Generally, colouring agents can be added to the mixed epoxy in quantities of up to 5% by volume and there will only be a minimal effect on the cured epoxy's strength. It's always advisable to make test samples to check that the colour and degree of opaqueness are right and that the mix has cured properly.

Please note that none of these colouring additives make the cured epoxy UV-resistant. So, limit their use to areas that are not exposed to sunlight or apply additional UV protection.

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