406 Colloidal Silica is a thickening additive used to control the
viscosity of the epoxy and prevent epoxy runoff in vertical and overhead
joints. 406 is a very strong filler that creates a smooth mixture,
ideal for general bonding and filleting. It is also our most versatile
filler. Often used in combination with other fillers, it can be used to
improve strength, abrasion resistance, and consistency of fairing
compounds, resulting in a tougher, smoother surface.