West System Colloidal Silica Filler 2 oz — Epoxy Thickening Additive, Non-Sag Paste

West System 406-2 Colloidal Silica is a finely powdered epoxy thickener that transforms mixed epoxy into a stable, creamy paste for fairing, filleting, and preventing runoff on vertical or overhead surfaces.

Whether you’re shaping a boat hull, building composites, or repairing bonded joints, controlling epoxy viscosity is essential. West System 406-2 is formulated to be blended into WEST SYSTEM resins and hardeners to produce a non-sag, workable paste that stays where you put it. It thickens without compromising cure or structural properties when used as directed, and it cures to an off-white, sandable finish suitable for fairing and finishing operations.

How does 406-2 change epoxy handling for vertical or overhead work?

Adding a small amount of 406-2 to mixed epoxy increases body and reduces flow, allowing you to apply epoxy to vertical faces and ceilings without sagging. This gives you better control during application and lowers the need for masking or temporary supports.

• Creates a paste-like consistency that resists runoff
• Improves placement when applying fillets or fairing coats on inclines
• Minimizes drip and waste on overhead repairs
• Compatible with WEST SYSTEM resin/hardener combinations

What are the benefits of using 406-2 in fairing compounds?

When blended into epoxy fairing mixes, 406-2 increases thickness and abrasion resistance, producing a smoother, more workable filler that’s easy to shape and sand after cure. The resulting fairing compound retains good adhesion and structural integrity when used as part of a proper epoxy system.

• Produces a creamy off-white paste suitable for finishing
• Enhances fairing strength and consistency for shaping
• Reduces shrinkage compared to solvent-based fillers
• Sandable once fully cured for a refined finish

How much 406-2 should I add, and how do I mix it properly?

Use colloidal silica sparingly — a little goes a long way. Add small increments to the mixed epoxy until you reach the desired viscosity, stirring thoroughly to eliminate dry pockets and ensure uniform texture.

• Start with a pinch and increase gradually to control thickness
• Mix resin and hardener fully before adding filler
• Stir thoroughly to an even, lump-free paste for consistent cure
• Avoid overloading, which can make the mix brittle or hard to wet out

Will 406-2 affect epoxy cure time or bond strength?

When used in recommended amounts with WEST SYSTEM epoxy, colloidal silica primarily alters consistency and has minimal impact on cure schedule or adhesion. It’s designed to be complementary; however, very high loadings can change mechanical properties and should be avoided for critical structural laminations.

• Formulated for use with WEST SYSTEM resins and hardeners
• No significant cure delay when used appropriately
• Excessive filler can reduce strength—use only as a thickener
• Best suited for fairing, filleting, and non-structural gap filling

Who is this for: West System 406-2 is aimed at boatbuilders, composite fabricators, professional repair technicians, and advanced DIYers who need predictable epoxy handling for fairing, filleting, and vertical or overhead repairs. If you require a sandable, non-sag paste that integrates with WEST SYSTEM epoxy products to improve placement and finish, 406-2 provides a simple way to adjust viscosity without introducing solvents or fillers that compromise the system.