I recommend you visit the West Systems and System Three websites to check out the available epoxy additives and their uses. I keep microballoons, flocking (milled fiberglass), wood flour (fine sawdust), calloidal silica (a "thixotropic" thickening agent - like ketchup it stays put when placed somewhere) and various glass and fiber matting. Things like new coffee filters make a great repair laminate with epoxy.


http://www.westsystem.com/ss/how-to-use/

http://www.systemthree.com/members/m_index.asp (The Epoxy Book in pdf is a free download and very worth reading through. Geared towards boatbuilders but the same facts apply to small batches for R/C)

Some additives bulk up the epoxy for filling gaps, some strengthen it, some change the properties (for better or worse) and they can be abused to make the adhering properties worse. Add too many microballoons to a large amount of epoxy and you may have a melt-down thermal reaction.

As mentioned above: always mix the epoxy first. Let it stand briefly to link and then add the filler(s).