406 Colloidal Silica: Thickening additive suitable for bonding, gap filling and filleting. It can be used to prevent resin flow on vertical and overhead surfaces and to control the viscosity of the epoxy. It is often used in combination with other fillers to control the working characteristics of an epoxy mix, e.g. improve the consistency of fairing compounds, to improve abrasion resistance etc. Add 2% to 10% by weight to the WEST SYSTEM epoxy mix. Cures to an off-white colour.