What is "micro"?

Hi guys,

I've seen many references to micro and dry micro in fiberglass work, but have never seen it defined (I searched, honest!). It seems to be a mixture of epoxy and something that's easy to sand. I've used flox before with cotton fibers, but it doesn't sand all that easily. Can you shed some light? Thanks.

Microballons made of glass.

So you see that refers to tiny glass micro balloons to fill the epoxy. When adding, I mix the epoxy first then add the micro balloons. Dry micro is like peanut butter, and will leave wisps when mixing that don't fall over. Be careful as you get to that point as you can add too much (many?) micro to the mix easily. If you let it sit for a minute and it pools, then it is not "dry" yet.

When set it sands nicely.

West System epoxy and fillers are widely used by many builders. It is readily available at large marine retailers like West Marine (which is not related to West Systems epoxy, just a naming coincidence).

West System has a wide variety of fillers that you can add to epoxy resin. If you get a brochure or go on their website, you can get a more info on each filler and their properties. They range from the lightest, non-structural fairing fillers to very strong, hard structural fillers.

In general, the lighter the filler the easier it is to sand and shape after it cures. The harder, stronger fillers are much more difficult to sand after curing.

You can also get cotton "flox" from Spruce. Flox makes for a very strong but hard sand filler.

I have a variety of fillers on hand and make up a custom brew to achieve the balance between strength and workability that I need.

Having built a Long EZ from plans in 1980s you become very familiar with micro and flox. The micro is basically ground up or small glass ( micro) beads. Finer that powered sugar. It is mixed to some desired consistency with the epoxy and is used as a slurry on foam core before the first layer of fiberglass is laid on. Also is used to fill any voids between multiple layers of glass. Micro in a bit heaver consistency is used to "pot in place" metal hard points for future layups ie wing attachments and etc. The third use is in finishing a FG component to ready for sanding or priming. The correct consistency will sand smooth for finishing. Flox is cotton fibers mixed the same way into epoxy. Doesn't sand well but very strong and bonds well. The AS catalog used to have a fairly good section on Epoxy , micro and flox use.

Thanks guys. So can primer and paint be applied directly over micro after it's sanded smooth? I'm envisioning all these little half-spheres of glass creating roughness, but perhaps they're so small it doesn't matter.

Thanks for the link, Bruce!

The size varies but the microballoons are like 50 microns (2 mils) in diameter. The first coat of primer fills in the 'voids'.
Adding micro reduces the strength of the epoxy; don't add it to any structural application unless you really know what you're doing.
Wear a dust mask when mixing; these things are so light they can 'float' up in the air.

BobTurner said:

The size varies but the microballoons are like 50 microns (2 mils) in diameter. The first coat of primer fills in the 'voids'.
Adding micro reduces the strength of the epoxy; don't add it to any structural application unless you really know what you're doing.
Wear a dust mask when mixing; these things are so light they can 'float' up in the air.

Click to expand...

Thanks. I'll order some and try it out.

BobTurner said:

Wear a dust mask when mixing; these things are so light they can 'float' up in the air.

Click to expand...

Another good tip is to keep your micro in a jar with a screw-top lid... plastic bags and snap-top containers make fairly good bellows, enough to make it look like it snowed in your shop. Walmart has big screw-top glass jars for a few bucks apiece.

mcb