Balsa Wood Sealant Hack

 The Thrifty Rocketeer blog continues...

A recent inquiry on Facebook about papering fins has triggered a memory of my learning about balsa wood sealing.  

 I learned the hard way about sealing your balsa nose cone before painting.  My first red nosecone looked SO good, I was proud of it until I launched the second time. The shock cord snapping the nosecone back against the top of the body tube (I presume) caused what is known as an "Estes Smile"... a curved indentation into the wood that mars the appearance.   

 Some wood filler and another coat of paint and I was good to go again.... and AGAIN it happened.  That's when I learned... 

I've done papering of larger fins once... using typewriter paper and a heavy slurry of wood glue and water. It worked well, but seemed to be more work than I wanted to go into.

 

Instead, from my very first rockets some ten years ago, I read about mixing a slurry of Elmer's wood glue (yellow) and just a few drops of water to thin it into a pore-sealing liquid. This was cheaper than buying a quart of "sanding sealer."  Some stores will sell a half pint of Min-Wax sealer also. 

 

The formula or recipe that I hit upon is this:

    1) Take the top off a 2 litter bottle of pop to use as your mixing bowl. 

    2) Squeeze about a half teaspoon of yellow glue into the cap. 

    3) Next, turn down your water faucet in the kitchen to only a drip droplet every few seconds. 

    4) Place your cap under the drip only long enough to catch one or two drips, then remove quickly. Turn off the water. 

    5)  Mix the glue and water together using a child's paintbrush until consistent. Note, ridges in the cap may attempt to keep the water and glue separate, from mixing. 

    6) Apply liberally to balsa surfaces when laid level to avoid drips or runs. Let dry completely. 

    7) Next, sand with fine sandpaper to remove any rough spots. 

    8) Wipe off any sanding dust and repeat with the next coating.

 

My experience is your first INITIAL coat should be 2 drops of water to a half teaspoon of glue to produce a watery coating. SECOND coat should be only ONE drop of water to the same amount of glue. Of course, if you run low or out of your mixture, you can whip up another batch in a minute. Alternatively, you can thicken the mixture just by adding a shot of glue to an already thin mixture, and stir well to become uniform.  Note, the mixture will thicken slightly in the cap, as it begins to dry. You can reconstitute the slurry with a drop of water and adding more glue. The hardened glue in the base of the cap will begin to dissolve into the mix also with stirring.

 

The resulting surface after two or three coats will have a yellow, firm appearance that is smooth enough to spray paint over. If you have ridges or bumps, sand again and use a slightly thinner mix to fill the valleys. Of course, each coating is adding weight, so your goal is a smooth, firm surface without adding too much weight. Always sand between coats... and always after the mixture has dried completely so you don't clog your sandpaper.

 

Rinse your paintbrush out after each coat, as it will tend to dry quickly and stiffen. A stiff brush can be loosened just by running the bristles under under water for a moment and between your fingers.  Yes, you can park your brush in a small Dixie cup of water between coats if you like... but it's not necessary. Rinse brush thoroughly before storing. You can toss the pop bottle cap out and get a new one for the next model kit.

 

So there you have it...  How to make a wood glue slurry to seal balsa wood surfaces.  I swear by it, though I have also used Min-Wax sealant from a local rocketry supply house.  My experience is that sealant dries faster, and the small jar tends to thicken up in the jar faster than you would expect.  If just a little thicker, you can recover a jar with a few drops of water, but once it becomes a gel... well, it's too late.   I like it, but it's a different consistency and dries quickly! 

I'd like to hear your thoughts on this "hack", as the younger kids call tips these days.  Until then, this has been the Thrifty Rocketeer saying, "Rinse your brush out before storing!"