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Hardener, filler and additive selection guides

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.

Hardener Uses Resin/Hardener Hardener Temperature Range (°C) Cure Speeds at room temperature
Pot Life 100g Working Time thin film Cure to Solid thin film
205 Fast
General bonding, fabric application
and barrier coating

206 Slow
General bonding, fabric application
and barrier coating

20-30 min 90-110
207 Special
Fabric application and coating for
natural wood finish

20-30 min 85-110
209 Extra
Slow Hardener™
General Bonding, fabric application
and barrier coating

50-70 min 200-260
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 Highest density Highest strength Lowest density Easiest sanding
3. Desired characteristics
404 406 403 402 405 407 409 410
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. Laminating
2. Bond layers of wood strips, veneers, planks, sheets and cores
3. Gap filling / 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.
420 Aluminium Powder
Moisture Resistance
Apply undercoats of epoxy modified for maximum
moisture protection.
422 Barrier Coat
Apply as a tough, low-friction coating, or as
a bearing surface when thickened with fillers.
423 Graphite Powder
Pigmented Undercoat
Apply an opaque, coloured epoxy undercoating
as a base for painting.
501, 503, 505 & 506 Colour Pigments

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.