Epoxy additives

How many of you use additives/fillers with your epoxy during construction? I usually use the WEST System 404 high density filler, even with 5-minute epoxy. This really allows for good placement and control of the epoxy during all phases of building, and I'm told the joints are much stronger. I also use the 410 microlight filler, but only for the final fillet surface at the fin/BT joint.

....I have used carpenters chalk mixed with west systems epoxy
to thicken the mixture ..I haven't tried any of the west systems fillers yet....

System Three Resins has a great publication called "The Epoxy Book" that delves into the various techniques involving epoxy, including additives. "The Epoxy Book" can be downloaded or obtained in an Epoxy Trial Kit from www.systemthree.com. Although more geared toward boat building and repair, System Three's information has helped me understand the proper way to use epoxy and additives.

Additives like silica fibers do increase the strength of your epoxy joints a great deal and I would continue using them. Also microballoons help to make fillets lighter and much more sandable. I use both on every rocket I build.

HTH, --Lance.

I'm a fan of microballoons personally, since they sand beautifully. Generally when you see a fin break, it does so in the wood itself and not the fillet. I'm told that microballoons actually take away from the strength of an epoxy fillet, but since the epoxy isn't the weak spot of the joint anyway, I don't think the microballoons will be a problem.

I have used Sig microballons for weight reduction in fillets. I figure the fillet is by far the most durable part of the assembly, even with the filler in it.