Micro-balloons vs wood flour

  I will be mixing up some fairing compound in a few days and I wondered how much to use. Compared to wood flour, what is the ratio? Twice as much? I assume that for fairing you want a drier mixture that when using wood flour as an adhesive?  I ask to estimate how far what I have on hand will go.

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RE: Micro-balloons vs wood flour


fwiw, on a spec sheet i found the following:

1.2L of mixed epoxy resin/hardener

Microballoons (dry bulk) 4 L

yields approximately 2 L of mixed compound

but the spec sheet is not clear what thickness of a mixture it is trying to get at...though i would guess its pretty thick given the ratio of dry microballoos to epoxy and my memory of when i did it last -- that said, there is a lot of variation depending on how thick you are trying to make your fairing mixture. 

if you are using it like a fill coat, it can be relatively liquid/gel like, if you are trying to make non-structural fillets, you are in peanut-butter territory.

when i am getting ready to work and i don't have a calibration, i make a small batch using tea-spoons (one tea spoon of hardener, two teaspoons of resin mixed in a cheap plastic cup, then measure out teaspoons full of whatever filler i am working with until i get the consistency i want and record the result. it's about the least wasteful i can get that i think is reliable.


RE: Micro-balloons vs wood flour

Dry mixtures are softer when cured, easier to sand, lighter and more difficult to apply.

Rich mixtures are the opposite.

I like to use a rich mixture for filling the weave, more of a slurry. For fairing I like a consistency of room temperature nutella or canned frosting. I never measure, juat add it in until the consistency is correct.

Good luck,



RE: Micro-balloons vs wood flour

  Thanks Howard. 

  You use the same method that I do, I was just trying to see how far a tub of balloons went. I have a Chester Yawl to fair inside and out and was curious if I needed to order more now. I figure that after scraping and sanding the epoxy, I will need to coat the whole boat at least once in and out before priming. 

RE: Micro-balloons vs wood flour

Do the microballoons change the color of the epoxy or do they turn clear when mixed (like cloth). Specifically, can they be used to fair areas that will have a bright finish? I had planned to just use lots of layers of epoxy and patience, but it would be great if I had a faster alternative.



RE: Micro-balloons vs wood flour

most brands i am familiar with have a redish color to them and are not compatible with a bright finish.  they do not turn clear when mixed with epoxy.

fwiw, bright finishes tend to be a bit more forgiving for slight unfairness (in terms of seeing a defect) vs a painted surface.  if you go with a rubbed varnish finish (not a wet/gloss finish) it hides minor surface irregulariies even better.

realistically, when building bright, i don't think you want to deal with significant fairing issues by just trying to layer on epoxy.  when building bright i tend to take a bit more care in my set up....knowing that i have limited ability to sand it out or build it up.

on sanding down, you only have a little less than a millimeter before you expose core.  on buidling up, you can build up another milimeter or two....and i would almost always do it with wetted out glass vs trying to do it with pure epoxy.  a significant thick (e.g., one or two milimeter) all epoxy layer typically develops cracks over time and is just heavy.  sometimes you can get even thicker than one or two milimeters.....but you need to have glass as part of the process.

my only other note is that as the builder, you tend to be more sensitive to noticing things that most folks will never see.  so you need to be careful about over-correcting. 

one great thing about building your own boat is that you can try it (less intervention) and see how it looks and then come back after the season and when you have time and take an approach that you didn't initially start with.  i tend to look at some of these choices through the lens of 'is it reversable'.  so if i have a small hallow that i am really not sure about, i can finish it and see what i think.  if i don't like the look aftewords, i can easily take a bit of varnish off and build up the epoxy a bit more. 

hope that helps.

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