Microballoons

I've been playing with microballoons as a thickener for epoxy fillets. I'm aware of the other fillers out there, but I happen to have microballoons handy and I have a question regarding them specifically.

Do microballoons sufficiently weaken the epoxy to where it becomes a concern for HPR applications (i.e. fillets)? If you've never tried them and are a little sloppy with your fillets, give them a try. It makes your epoxy sand like a dream! Make sure you have a good filter mask on though, because apparently the stuff isn't real good for your lungs.

Here is an excerpt from the System Three epoxy reference book (used to be a free PDF on-line). Micro-balloons are what I needed for my fillets on the Upscale Big Brute.


"Microballoons and microspheres should not be routinely used
in an adhesive formulation as they reduce tensile strength.
Quartz microspheres may be used as a filler/thickener for cold
molding where the surface area to be bonded is large with
respect to the mass. Microspheres are acceptable here because
of the large glue surface area involved and the low
microsphere loading level."

I just posted a reply on the "Big Brute" thread about microballoons! Sounds like you want to avoid using them in places where you are using the epoxy for a strong bond, but for fillers, they are fine.

Just to confirm...
Microballoons are:

• good for fillets
• bad for fillets

as far as strength goes on holding the fin to the body tube?

My impression is that the microb's would help transfer the load over the area the epoxy is placed, therefore, causing less fillet cracking from abrubt impacts. Any other thoughts?

For strenght instead of micro ballons in epoxy use West System high density micro fibers...I think it's 805..

Don't remember for sure...used them all up on Carl's nose cone.

Only one drawback...turns the epoxy bright PINK!

sandman