Common Fillers
Fumed Silica (Aerosil 200, Cabosil, etc.)
Typical Applications: stronger tougher putties
Easy to mix with resin and very tough, smooth and easy to spread, very hard to sand.
Glass Microspheres (Q-Cell)
Typical Applications: softer putties
Mixed with resin makes a softer easier to sand putty, not as strong, suitable for radiusing, fairing, etc.
Mill Fiber (Short ground fiberglass)
Typical Application: very tough fiberglass putties
Very difficult to sand but exceptionally tough.
Mixing Putty
Always add filler to resin to start, add filler until your desired consistency is reached, a lot of people will refer to this as peanut butter.
Putties can be stored for a quite a while in this form, but a good rule of thumb is roughly as long as the raw resin would be stored is ok.
For these putties, catalyization will be based on roughly the volume of resin in the original putty. We like to use a formica plywood board and mix shop putties just like bondo. With a putty knife and a small mound in the center of the board to pour catalyst into. With care this can be done without too much mess.
By: Capt. Ken