How to Make Balsa Wood Dough

If you have been building balsa models for any time at all then I'm sure you've tried various putties and fillers.  I've tried just about everything that has been marketed.  I've used spackling compound, Model Magic-type stuff (hate it), micro-balloons mixed with about anything that will stick to balsa and a myriad of other things.

So far, none of them has been good enough for me to stop my search.  There are a variety of problems with commercial fillers.  In fact, some of them are so bad that I think the folks marketing them have never actually used them on a model or they would know how bad the stuff is.

Some of the fillers work ok, but there are still properties that could be better.  These are just a few of the problems with various fillers that have come and gone over the years:

• So hard to sand that it leaves a ridge
• Doesn't sand at all - usually means it's rubbery
• Too brittle (normally these are the extremely light fillers)
• Dries so fast it can't be applied properly
• Doesn't stick and falls off
• Poor color match

Over the years I've experimented using cellulose-based glues, such as Ambroid, to make filler.  These glues sand very easily and stick well.  The two problems I've had with them is that they are generally too dark and they dry so fast I often don't have time to get the filler in place.  At that point it starts crumbling off while I'm still trying to work with it.

Nevertheless, I still felt that a cellulose product was the proper base.  I just had to work the kinks out.  I finally have.

Mixing the Dough

The two basic components of the dough are clear dope and balsa dust.  The dope can be butyrate or nitrate.  I've tried both and didn't notice a difference in working with them.  The dope has a longer working time than Ambroid and is less expensive for a larger quantity.  Although I've never done it, I assume that retarder can be mixed in if you need even longer working time.

	You will need to collect balsa dust until you have a few tablespoons.  You don't need to make a pint of this stuff all at once.  In fact, if you don't care about working out a good color match, you can make it as needed. I can always retrieve plenty of fine balsa dust from my table saw.  A disk sander also produces lots of dust. If you plan to retrieve dust from a power tool, then you should clean it out before you use it with balsa.  That will minimize the amount of foreign particles, such as plywood, plastics or metals, that end up in the mix.
	If you don't have a power tool to create dust for you then you can just scoop it up a little at a time as you sand.  Before you start, clear off the area so you don't get a lot of foreign particles mixed in with the balsa dust. The more you sand, the more dust you get.  The more you sand, the less filler you need.  It's a catch 22 in a good way.
	The other thing my table saw produces plenty of is balsa strings.  After collecting the dust, put it through a fine strainer to sift out larger particles.  Fine dust is easier to mix and to apply.
	Sifted balsa dust.
	Mix in the clear dope in small quantities.  It's a good idea to keep some of the dust in reserve in case you accidentally add too much dope.  If the reserves aren't enough, just set the mix aside until you create more dust. It is mostly personal preference how thick you want your mix to be.  I like mine to be like thick, gooey oatmeal.  I want it to be sticky, but able to be spread.  The more solids in the mix (dust) the less it will shrink as it dries.  For that same reason, I use the dope full-strength (no thinner).
	These were the solution to the other problem.  When the dough dried it was lighter in color than when it was wet, but it was still too dark. I lightened the color slightly with talc.  Micro-balloons accomplish the same thing.  However, you will have to experiment if you really want a close color match because the dough is a different color dry than wet. Balsa also has a variety of shades.  If you really care, you may want to make up a bunch of 1/2 oz. bottles of different shades.  You could slop a small glob on top of the lid to match the color.  That's even too anal-retentive for me.  One jar that's close enough works.

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Copyright © 2004 Paul K. Johnson