CABOSIL THICKENING AGENT – Fumed Silica (aka Cabosil) is an extremely fine powder used to thicken virtually every liquid material. It is typically used to thicken resin, paint, dyes, and even water.  It is great for making fillet putty, thickening epoxy for a better glue consistency, and for use below the waterline. Resin mixed with Fumed Silica (Cabosil) is an ideal product for repairing the blisters that are so common on fiberglass boats.
 
It is used in approximately a 1:1 ratio to the mixed resin by volume.  This will provide a consistency similar to vaseline. You may use more or less to suit your application. It adds a milky white color to the resin.
 
Silica is an agent which is used to control the thixotropy or ‘sag’ characteristics of a resin system. By adding colloidal silica powder in varying amounts to a resin mix the handling and flow characteristics can be controlled. Relatively small quantities added to a resin mix containing glass bubbles or micro balloons will give non-sag properties and impart easier handling. Silica is also used with microfibres to produce a mix suitable for use as a high strength, non-sagging structural adhesive, particularly for non-absorbent materials such as grp. The inclusion of colloidal silica has the effect of increasing the hardness of the resulting mix which will create more difficulty when sanding. For this reason silica is usually added in the minimum quantities to any mix for which sanding is anticipated. In some applications this feature can be used to an advantage, for example to create a hard wearing edge or surface.