>> Is there a recommended ratio of epoxy to balloons? <<

You mix the epoxy, then gradually add microballoons until you achieve the consistency you desire.

A thin mixture, like runny mustard, is easy to put on the boat and then distribute with a spreader or foam roller. Because it's thin you'll probably need several coats to build it up enough to fair anything more than minor scratches.

A thick mixture, peanutbutter-like, you can trowel on with your spreader. Pay attention to getting the surface smooth as you apply it. Saves lots of sanding later.

>> And do I need to add anything else?  Some talk about adding wood flour (which I have) and others suggest adding Silica thickener (which I don't). <<

Colloidal silica (eg: Cab-o-Sil) and colloidal cellulose (eg: Cell-o-Fill) act as stabilizers for the mix because of the physical properties of their molecules. They help reduce sagging and running - which is helpful when you're trying to apply thick coats. Because they're also thickeners I add them to the mix before the microballoons. That way I don't over-thicken. My preference is colloidal cellulose because it's easier to sand.

Wood flour is a filler but not a stabilizer. Think of it as a substitute for the microballoons - that's how the epoxy matrix will see it. Wood flour is also a lot coarser than microballoons but way cheaper. If you need to build up a thick fairing I think a layer of epoxy + wood flour, with a top coating of epoxy + microballoons might be the ticket.

Hey Keith,

First, completely mix the epoxy and hardener, then pour the mix into the balloons and stir. That avoids lumps.

The ratio depends on what you're using it for. If you're filling the weave, a runny slurry is a good consistency, especially if it's your first time using microballoons. For fairing, a thicker consistency is better. I personally like something like canned frosting or hydrogenated oil smooth peanut butter.

You can also use the frosting consistency for filling the weave, but that takes some practice to get it into all the squares made by wet-out woven cloth without leaving voids. If you're in a hurry and want a more predictable result with a lower learning curve, I'd recommend a slurry coat to fill the weave followed by a frosting coat for fairing.

I can think of absolutely no reason to add woodflour to a balloon mix. If you know why they recommend it, I'd be interested in hearing. It would make the result heavier, harder and more difficult to sand.

Colloidal silica is used to make a thick mix spread more easily. A thick balloon mix, when applied with a squeegee will roll and not want to sit flat on the first pass, especially if applied in a thick layer. Adding silica will make it apply more smoothly. It will also make it cure harder and be more work to sand.

Rather than adding silica, I prefer to take my time and use multiple thinner coats instead of one big fat one. That's why I always use slow hardener for balloon mix. If the mix still doesn't want to spread well, you can always add a little more epoxy mix.

As far as mix ratios, I'm sorry but I always mix mine by feel. Start with some small batches, say 3 oz of epoxy/hardener mix and do some small scale applications until you get the feel of what you're doing. Then, as with so much of this, just when you get it perfect it'll be over and time to move on to the next new process you have to learn. That's why so many of use end up building a second boat :-)

Good luck,

Laszlo

   I love this forum.

Thank you for the quick replies.   Should be an interesting day!

Keith

Keith, glad to help.

Chenier, I didn't mean to sound rude to you. You posted while I was still typing so I didn't see your reply before I wrote mine. If I had, I would have worded my stirring recommendation a bit differently so that it would have shown respectful disagreement instead of apparentlty rudely dismissing you. Sorry.

Laszlo

No worries, Lazlo. Didn't bother me a bit. And I learned something. :)

Thanks for apologizing. It's getting harder and harder to find good manners on the internet!

Regards,

Chenier