WEST SYSTEM Epoxy: Product Selection and User Guide

WEST SYSTEM is a modular marine epoxy system: resin is combined with a compatible hardener, then fillers or reinforcement are selected for coating, bonding, fairing, filleting, laminating or repair. Reliable results come from choosing the complete system and following the stated pump ratio, surface preparation and cure conditions.

This page is a searchable field guide to the product family and the essential workflow. The current WEST SYSTEM User Manual & Product Guide remains the controlling source for ratios, cure windows and application details.

Build the right system

The standard WEST SYSTEM approach uses 105 Epoxy Resin with a compatible WEST SYSTEM hardener. Hardener choice affects cure speed, working time and some finished properties. Metering pumps are matched to specific resin/hardener combinations; they deliver the correct ratio only when the proper pumps are installed and each pump is given a full stroke.

Fillers are added after the unfilled resin and hardener have been mixed. Low-density fillers create easily sanded fairing compounds. Higher-density fillers improve strength, abrasion resistance or hardware bonding. Colloidal silica controls sag and improves gap filling but makes sanding more difficult.

Product selection guide

• Clear coating and fiberglass wet-out: use the selected resin/hardener blend without filler, then apply reinforcement or subsequent coats within the permitted window.
• General bonding and fillets: add a structural or adhesive filler to the mixed epoxy until it reaches the required non-sag consistency.
• Fairing: use a low-density fairing filler and apply only over a properly prepared, compatible substrate.
• Hardware bonding: use the manual’s fastener-bonding method and a high-density filler where required.
• Difficult or flexible substrates: consider G/flex specialty epoxy where its product guidance supports the material and movement.
• Convenient small repairs: a pre-thickened WEST SYSTEM adhesive may reduce measuring and filler selection, but it still needs correct preparation and cure conditions.

Essential epoxy workflow

1. Define the job and substrate

   Identify the material, load, moisture exposure, service temperature and whether the goal is coating, laminating, bonding, filling or fairing. Verify adhesion guidance for plastics, metals, treated woods and previously coated surfaces.

2. Select resin, hardener and additives

   Choose the hardener for the working temperature and time. Confirm pump compatibility. Select fillers, fabrics, pigments and coatings as a complete system rather than treating them as interchangeable accessories.

3. Prepare the surface

   Make the substrate clean, dry and sound, then abrade as required. Remove amine blush from cured epoxy with water and an abrasive pad before sanding or recoating when the manual requires it.

4. Dispense the exact ratio

   Use the correct calibrated pump set or weigh components only where the manufacturer supplies a weight ratio. Use full pump strokes and keep track of each stroke. Do not alter the ratio to speed or slow cure.

5. Mix thoroughly

   Stir resin and hardener for the specified time, scraping the sides, bottom and corners. Transfer to a clean container and mix again for critical work. Add fillers only after the base epoxy is completely mixed.

6. Apply a neat coat for bonding

   Wet porous bonding surfaces with unfilled epoxy before adding the thickened mixture. Fit the joint while the wet-out coat is still receptive and clamp with enough pressure for contact without squeezing the joint dry.

7. Control heat and batch size

   Mixed epoxy cures faster and becomes hotter in a deep container. Pour coating batches into a roller pan or apply promptly. Divide large jobs into manageable batches and never leave a reacting mass unattended.

8. Recoat or prepare after cure

   Recoat within the stated chemical-bond window when possible. After cure, remove contamination or blush as directed, then sand to the specified profile before paint, varnish or additional epoxy.

Common mistakes

• Using pumps that are not matched to the resin and hardener
• Partial pump strokes or losing count
• Changing the mix ratio to change cure speed
• Adding filler before resin and hardener are mixed
• Bonding to moisture, dust, wax or unsupported old coating
• Making a deep batch that overheats in the cup
• Clamping so hard that the adhesive is squeezed out
• Coating blush or contamination without washing and preparation

Frequently asked questions

Can I change the resin-to-hardener ratio to alter cure time?

No. Use the specified ratio and choose a faster or slower compatible hardener for the temperature and working time.

When do I add filler?

First mix the resin and hardener completely. Then add the selected filler gradually until the mixture reaches the consistency required for bonding, filleting or fairing.

Do I need to remove amine blush?

Some cured epoxy surfaces develop a water-soluble film. Follow the manual: wash with water and an abrasive pad, dry, then sand as required before overcoating.

What is G/flex for?

G/flex is a toughened specialty epoxy intended for demanding bonds and certain flexible or difficult substrates. Confirm surface treatment for the exact material.

Sources and further reading

• WEST SYSTEM: User Manual & Product Guide
• WEST SYSTEM: Current User Manual PDF
• WEST SYSTEM: 105 System Selection Guide
• GoIndustrial: Surface Preparation
• GoIndustrial: Bonding Surfaces
• GoIndustrial: Adding Fillers to Epoxy

This guide provides general educational information. Products, substrates, site conditions and regulations vary. Follow the current technical data sheet, package directions and safety data sheet for every product you use. Code-regulated, structural or safety-critical work may require a qualified professional.