West System Colloidal Silica Epoxy Thickener 406 — Off-White Paste for Fillets & Fairing

When working with WEST SYSTEM resins and hardeners, controlling flow and body is essential for vertical fills, fillets, and fairing compounds. 406 Colloidal Silica is formulated in the USA as a high-performance fumed silica that increases viscosity without undermining the cured epoxy's integrity. It helps you tailor epoxy consistency so you can place material exactly where it’s needed—on faces, edges, and overhead surfaces—while producing a smooth, sandable finish suitable for structural and fairing applications.

How does 406 Colloidal Silica change epoxy handling?

Adding a small amount of 406 transforms thin epoxy into a thixotropic paste that resists sagging and dripping. You can easily control how thick or spreadable the mix becomes by adjusting the amount of powder, giving you predictable placement on vertical or angled surfaces.

• Create non-sag fillets and edge fills for joinery and laminates.
• Convert laminating epoxy into a brushable or trowelable fairing compound.
• Maintain workability long enough to shape and finish before cure.

What performance changes occur after cure?

406 Colloidal Silica principally modifies the uncured epoxy's rheology; once cured it forms a uniform, creamy off-white paste that remains structurally stable. While it thickens the mixed epoxy, it does not change the fundamental cured strength of properly mixed WEST SYSTEM resin and hardener systems when used in typical fairing and filleting ratios.

• Cures to a sandable, abrasion-resistant surface suitable for finishing.
• Adds bulk and body without significantly reducing bond performance when used correctly.
• Stable color and texture for cosmetic and structural touch-ups.

How much should I use and how do I mix it for best results?

Start with small increments: add powder a little at a time until you reach the desired body. Thoroughly blend the silica into a fully mixed resin/hardener blend to avoid streaks; using a stirring paddle or disposable mixing stick helps achieve an even, lump-free paste.

• Add in measured spoonfuls to control viscosity precisely.
• Mix until homogenous—no visible streaks or clumps remain.
• Use within the epoxy’s working pot life; don’t extend cure time by excessive cooling or dilution.

What projects benefit most from 406 Colloidal Silica?

Use 406 wherever you need epoxy to stay put: building fillets, fairing hulls, filling gaps, or applying a trowelable filler before sanding and finishing. Its creamy cured texture makes it ideal for cosmetic fairing as well as reinforcing structural joins where sag-free placement is critical.

• Vertical and overhead repairs where runoff needs to be prevented.
• Creating smooth fairing layers that are easy to sand and shape.
• Mixing into epoxy putties and bulkers for improved consistency.

Who is this for? 406 Colloidal Silica is for boatbuilders, composite technicians, woodworkers, and DIYers who use WEST SYSTEM epoxy and need precise viscosity control. If your work involves vertical bonding, fairing, or any application where drip-free application, smooth finishing, and compatibility with WEST SYSTEM resins matter, this additive gives you predictable handling and a sandable finish without compromising the system’s established performance.