Hi John,

  It depends on what you're going to use it for. A fillet should be something like peanut butter, filling wire holes a little thinner. Here's a link to the CLC instructional video about using a ziploc bag as a dispenser for fillets. Hope it helps.

 Link

That video's for wood flour thickened epoxy, not microballoons. The microballoons are a dark purple color.

The consistency depends on what you're using it for. If you're filling the weave, then it should be a somewhat thin slurry, like a milkshake. If you're fairing it should be as thick as you can handle. The thicker/dryer it is, the easier it is to sand it and the less your epoxy bill will be.

If you make it too thick and dry, it will curl over onto itself during application. It can get pretty difficult to get a smooth application with a really dry mix. Making it thinner (adding more epoxy) makes it smoother. I like to go fo something like cake frosting.

And remember - microballoons should never be used to make glue. They don't have enough shear strength so the joint will be weak.

Have fun,

Laszlo

So when do you use Microballoons, and why?

Thanks

Michael

Microballoons are great for filling weave and for fairing. They're literally balloons - microscopic hollow spheres - made from phenolic plastic. They are very hard to crush.

When mixed with epoxy, they form a lightweight filler material with a hard finish that stands up well to pressure and is easy to sand. Think of them as a controlled way of mixing air bubbles into epoxy to make a tough foam. Because they displace the epoxy, the end product is lighter and cheaper than using straight epoxy. It's also much easier to sand.

Because of its qualities, it's better in most cases for filling the weave and it's especially good for fairing. A thick mix can quickly fill in the nastiest hollows and it's easy to sand when cured. Once it's sanded, the next step is to seal it to close off the broken balloons at the surface. A 2-part high-build primer is ideal for this.

The main reason that you don't see much mention of the stuff here is that it's a sort of hideous purple color. You can't use on a surface that's destined for varnish. Under paint or graphite/epoxy, though, it's great. I've used it to fill the weave on the bottoms of all my current boats, as well as for fairing my sailing dinghy (which is painted inside and out).

Because of all the hollow spaces in the mix, it cannot be used for thickening epoxy to make glue, at least not where the joint will be under significant structural loads. The bubbles will act as stress concentrators and the  glue will fail.

Hope ths answers your questions,

Laszlo