Cab-o-sil vs microballons

[mlwynn]

I need help from the composite masters.

I have searched but cannot find the answer. I understand the difference between cab-o-sil and microballons in terms of what they are. I know they are both used as non-structural fillers. I have not been able to figure out when to use one and when to use the other.

What is the difference in application?

Thanks,

Michael Wynn
RV 8 FWF (working on the fiberglass)
San Ramon, CA

[DanH]

"Thickener" is a fair description for cabosil, but to be precise it doesn't thicken epoxy as much as make it thixotropic; doesn't flow except under pressure.

If a fabric layup has a lot of vertical I'd suggest a faster hardener to get a short gel time while still maintaining good initial wet-out. Cabosil might make the fabric a bit more difficult to wet out. I've never used any in a fabric layup, so I don't know for sure.

Add cabosil to a micro/epoxy filler mix if your epoxy sytem has a a slow hardener and the surface is vertical. Even dry micro will flow off on the floor if the epoxy system takes hours to gel, and a lot of the structural epoxies are quite slow. Using something like West and fast hardener you don't really need the cabo; not much flow time. Heck, with West the trick is to get micro mixed and spread before it exotherms.

Best use for cabo is mixed into epoxy for structural glued joints, like in wood wings. The epoxy does not run out of the joint. With cabo you can also form an epoxy filet on tee joints merely by wiping the joint with your fingertip.

Microbubbles are just that, bubbles filled with air, so micro/epoxy is not usually considered structural. Flox is cotton fiber; flox/epoxy mix is structural.

[scsmith]

In small doses, cabosil makes epoxy harder, more durable, more compression strength. If you add too much, it can degrade the other good properties of the epoxy.
Use enough to keep filler from sagging or flowing, no more.

My rule is no more than 1/3 as much cabosil as filler, whether it is flock or microballoons.

As Dan H mentioned, do not use cabosil for fabric layups. If you are having trouble with a layup moving around, try using a peal-ply of 100% polyester interfacing fabric ( about a dollar a yard at fabric stores) OR, kind of a poor-man's vacuum bag, put seran wrap over it.

Good luck. Composites are not evil as many RV-ers seem to feel. I swear sometimes it sounds like a religious argument. Its mainly just a different skill set, but once you have some experience, it is very adaptable, forgiving, versatile.

[mlwynn]

Thanks, guys.

That really clarifies my understanding of the additives. Thanks. I have actually been enjoying the fiberglass part of the project. In most ways, much more forgiving than aluminium. Lots messier, but that is just temporary.

Regards,

Michael Wynn