Cab-O-Sil is a viscosity regulator, itsthe best epoxy additive if you are working on vertical surfaces, it will make your epoxy mix more thixotropic, meaning it won't run. Don't use in large amounts if you intend to sand it, its very hard to sand, (delivered from quartz). Makes a very good structural adhesive
It can also be added along with other fillers such as calcium carbonate to create a thixotropic, hard wearing, scratch resistant tooling gel coat.
Slowly apply to resin until desired consistency is acquired. Usually 1 part filler to 2 parts resin if using it alone.