West System Microfibers Epoxy Filler 6 oz — 403 high-strength non-slumping structural paste

West System 403 Microfibers is a fine-fiber epoxy thickening filler that turns mixed WEST SYSTEM resin and hardener into a high-strength, non-slumping gap-filling adhesive for structural bonding and repairs.

Designed for boatbuilders, woodworkers, and repair professionals, 403 Microfibers thickens WEST SYSTEM epoxy to a controllable, paste-like consistency that bridges gaps, penetrates wood grain, and forms durable structural bonds. Unlike lightweight fillers that bulk out resin, this blend of fine fibers reinforces the cured epoxy for improved shear and compressive strength. It works with 105-series resins as well as WEST SYSTEM G/flex and quick-setting G/5, giving you one reliable product for many bonding and repair tasks.

How does 403 Microfibers strengthen epoxy joints?

Adding 403 Microfibers to mixed epoxy creates a fiber-reinforced adhesive that resists crushing and shear under load. The fibers disperse through the resin, improving internal support and preventing brittle failure compared with neat epoxy.

• Produces a tough, structural paste that stays where applied without slumping.
• Fibers help transfer load across gap-filled joints for stronger bonds.
• Improves resistance to compression and shear relative to unfilled epoxy.

How do I control the consistency for different repair jobs?

Consistency is determined by the amount of 403 added to mixed epoxy—small amounts make a spreadable adhesive, larger amounts create a thick bedding compound. Measure and record the ratio you prefer so repeat batches match, especially when working in stages or on multiple components.

• Add a little filler for thin gap wet-out and surface adhesion.
• Increase filler for gap-bridging, non-sag structural bonds in joints.
• For consistent results, duplicate the filler volume per batch during multi-part projects.

What materials and epoxy systems is 403 compatible with?

403 Microfibers was formulated to thicken any WEST SYSTEM epoxy, including 105 Resin mixes, G/flex for flexible, tough bonds, and the rapid-setting G/5 adhesive. It is particularly effective when bonding and repairing wood, but also suitable for many composite and general-purpose structural applications.

• Works with 105 Resin-based WEST SYSTEM formulations for standard structural uses.
• Compatible with G/flex for joints needing toughness and some flexibility.
• Can thicken quick-setting G/5 for faster, gap-filling adhesive work.

How should I use 403 Microfibers for best results?

Mix your resin and hardener first according to the epoxy system instructions, then gradually fold in 403 until you reach the desired thickness. Apply the filled epoxy to clean, prepared surfaces and clamp as needed until the compound cures; for repeat batches, weigh or measure the filler to preserve identical viscosity.

• Mix resin and hardener thoroughly before adding filler.
• Add filler incrementally while stirring to control viscosity precisely.
• Use clean, dry surfaces and clamp parts for reliable structural bonds.

Who this is for: West System 403 Microfibers is aimed at professionals and serious hobbyists who need a dependable, high-strength epoxy thickener for structural bonding, wood joinery, and repairs that require gap-filling and load-bearing performance. If you build or repair boats, restore wooden furniture, or perform demanding composite repairs and want consistent, reinforced epoxy adhesives that work with WEST SYSTEM resins, this 6 oz package is a compact, effective option to keep in your workshop or tool kit.