Sealing and Painting Balsa
 

I sheeted the aluminum landing gear on a plane I am finishing. I decided to paint rather than cover the legs. This was a test for me getting into new stuff. If the sheeting doesn't pop off the first time I land I may redo it in a more professional manner.

I sanded the balsa and covered with about four coats of Duplicolor Filler Primer. I also sanded it at least twice while priming. I then sprayed with Duplicolor top coat. As you can see in the pic I didn't do something enough because you can still see the grain in the wood.

So I'm looking for some ideas on how to get a nice smooth finish on balsa without glassing, just sealing and painting.
Thanks, Steve

RE: Sealing and Painting Balsa
 

Search for Balsarite. Used it years ago for sealing balsa prior to covering, I think they also made a formula for sealing prior to painting.

RE: Sealing and Painting Balsa
 

Not sure how what you're doing will work, I'm gonna watch closely. I can tell you from what I've seen that a wing just sealed and painted, the balsa eventually splits. I have an old JU-52 I got at an estate sale. The wings are not glassed or mylar covered, just sealed and painted. At home I noticed the bottom of the wing had several splits in the sheeting. I've also seen this on planes for sale at swapmeets that were finished the same way.
Edwin

RE: Sealing and Painting Balsa
 

While not your preferred method, glassing is going to be the fastest way to seal the balsa and add some strength to boot. Unfortunately at this point it is really not an option as epoxy resin is not going to stick to paint. With what you have now, I would cover with one of the iron on fabric coverings and then paint. Can I inquire as to why you have no interest in glassing?

RE: Sealing and Painting Balsa
 

You have to use something stabilize the grain and keep the resin from soaking into the grain. 3/4ounce glass cloth and epoxy is your best bet. You can also use tissue and dope or silkspan to achieve the same effect at the sacrifice of ding resistance. Some old timers use dope and talcum powder to seal the grain then prime and paint. Very light, but prone to dings as well.

RE: Sealing and Painting Balsa
 

I'm not looking for a way to "fix" what I already did. The current covers were just a test. The only reason I said no glassing was being lazy, in addition to having never done it before. Seems like glassing would talk a good bit of skill. If the covers stay on and don't break on the first landing I may redo them and that is what I am looking for ideas. I found some old comments where it seems quit a few people use dope and talc as a sanding sealer. I will look into the dope thing. I've also found comments where people used diluted white glue and talc.

RE: Sealing and Painting Balsa
 

Interesting thread in that none of us have investigated or found a replacement for the 100 year old nitrate/byuterate doping processes. Esp. in light that the products seem to be going away.

I wonder what the 1:1 scale ceconite community uses to seal and fill in wood grain? Then again more than half of the 1:1 ceconite community refuses to follow ceconites STC'd processes and use the appropriate plastic "dopes" and they resort back to the specifically warned not to use on ceconite nitrates and byuterates.

Then what do the wood working and nautical boat building communities use?

RE: Sealing and Painting Balsa
 

Have you looked at any of the "Liquid Sheeting" products?

RE: Sealing and Painting Balsa
 

Ok, fillers come down to personal choice and whats available to you. I'd go with balsarite, its light and easy to sand etc, many fillers are hard and its so easy to sand a skin next the filler away to nothing. if you want to seal and fill and then paint, I'd suggest another alternative, polyesther resin with microfibres or balloons, mix it thin and spread evenly. i find old credits cards work very well for applying, best results given working diagonal to the grain. Why I like polyesther over epoxy is it works well thinned down and with retarders to give you working time, and still paints well.

The Cracking issue is in reality quite simple in its causes, All the balsa is only sealed from the outside, the inside is still quite raw and quite happily still steadily drying out some more over the years, even in storage. What happens is the balsa absorbs moisture during humnid spells and then losees it again during low humidity, the movement isn't a lot but it slowly draws all the resins and oils out of the balsa's grain which is why it slowly shrinks and cracks. Its these oils and resins which give the balsa {and any timber} its structural integrity.

I am a cabinetmaker/joiner/shipwright, and over the years have seen mny change as to filling sealing and coating woodwork. My personal preference for coatings and fillers is the urethane family, they give the best long lasting results in harsh enviroments.

RE: Sealing and Painting Balsa
 

If you really a grain free finish that will last for years and is very easy to apply then get yourself a qt. of Minwax oil based urethane and some 3/4 oz. cloth, it goes on fast and easy, then prime and paint...

Bob

RE: Sealing and Painting Balsa
 

I like to use 0.75 oz cloth, polyester resin (inexpensive and less health hazard relative to epoxy) and microballoons. It creates a very durable finish that accepts paint and foils well.

RE: Sealing and Painting Balsa
 

I think you will need to seal the Balsa completely because humidity will continually be changing the surface under the finish if you don't .. Balsa is thin and soft and very effected by moisture in the air.. That is why we have so many wrinkle's show up in our covering .. If getting a good finish on the wood is important you might need to do a little more work than you first thought or possibly come up with a different material or method.. What about covering over the balsa on the the gear with Iron on covering ? I have Century 21 covering on my Robart landing gear and it was easy to do and looks great.. It can also be painted if need be...

RE: Sealing and Painting Balsa
 

Yes, I have experimented with the white glue/talc sealer. My testing showed that AT LEAST 3 coats of white glue and 3 coats of filler primer sanded after every coat gave a pretty nice finish. But that was the minimum number of coats using that method.

RE: Sealing and Painting Balsa
 

I've seen many good comments here - agree with most of them (about 98%). However, I've got an observation and then a question; you're sheeting the aluminum landing gear - that's great. How do/did you adhere/lock the wood to the aluminum, knowing that landing gear bends/gives and wood doesn't do that well? If you didn't, the wood won't stay there very long without vibrating itself to dust.

RE: Sealing and Painting Balsa
 

In the long axis there is a bit of flex in the balsa. But what I am doing is a test as much as anything else. I let the balsa float on the legs. It is only glued on the end pieces. We will see how it goes on it's first flight.

RE: Sealing and Painting Balsa
 

Dope + Talcus. An old solution, as old as easy to sand is.

RE: Sealing and Painting Balsa
 

RE: Sealing and Painting Balsa
 

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RE: Sealing and Painting Balsa
 

some of the very lightweight spackle products work well also, but as has been pointed out, not very ding resistant.
you could skip the fiberglass entirely and go with just finishing epoxy... but that can get heavy.
+1 on silkspan / tissue paper, and talc / dope.
I've used the liquid sheeting products with great success, but only (so far) on Styrofoam.

RE: Sealing and Painting Balsa
 

My favorites are as follows, based on weight, lightest first and assuming we are talking RC gas or glow models:

Japanese tissue/ Esaki and nitrate dope for bedding the tissue. Lite silkspan and nitrate are in the same league. Jap tissue is sealed in about 2-3 coats while lite silkspan in about 4. It's litest for gas and glow apps but not ding resistant. It's very thin
A close second is carbon veil and nitrate. This takes more effort since the veil is very sheer with lots of open areas that need filling, but is also very thin
Mediumsilkspan and nitrate dope for bedding
Japanese tissue or lite silkspanand Klass Kote clear epoxy paint. Epoxy paint is heavier than nitrate. So is urethane paint
Polyspan PET tissue and nitrate of KK epoxy paint. Polyspan is heavier than the paper tissues

I typically will bed with nitrate and make ready for primer in KK.I like KK primer; sands extremely thin

Then come the lite glass cloths, prefernce being the 0.6 ounce and epoxy paint. But it's heavier but no more ding resistant than the above

If you want ding resistance, you will need thickness and weight. Either epoxy finishing or laminating resin works well or polyester/vinylester finishing resin. BUT weight is a problem so if yours is not a weight issue, use that technique.

RE: Sealing and Painting Balsa
 

Lately I've been trying silkspan or tissue applied with Sig Stix It instead of Nitrate dope. Stix it goes on nice and then you can iron whatever you want onto the surface. Then a couple pf coats of clear nitrate dope and you will have a light weight, stable, smooth surface to paint. If you want a glass like surface fill with nitrate dope and talc.

Need a lot more strength for not much more weight? Try Polyspan ironed on with Stix It. Much stronger than silkspan but also more expensive. On larger planes Sig Koverall works well and is not too expensive, apply with Stix It and seal with nitrate dope.

Fiberglass cloth and epoxy or polyester resin is just too messy and heavy for my taste. Been modeling for 40 years and never felt the need to try it more than once or twice, never turns out as nice as the traditional silkspan and dope.

Nitrate dope is compatible with just about anything, not so with epoxy or polyester resins. Plus nitrate dope ALWAYS cures, sometimes epoxy or polyester resins don't.

RE: Sealing and Painting Balsa
 

Has anyone tried Titebond II or Titebond III with micro balloons?

RE: Sealing and Painting Balsa
 

I have tried sealers with mixed results, usually not the smooth surface I was looking for. Just breaking down and glassing the surface may be the easy way. I have been using the Deft Sanding Sealer for my glassing for a log time and like the ease of using it but just discovered something after blowing out a fuel tank seam with a YS engine and blowing 10 ounces of fuel through the fuse, it isn't as fuel proof as I thought it was. I almost never glass any glow powered planes but this is the one I did. :eek: It lifted the glass from the inside out a little, more like bubbles.:eek:

RE: Sealing and Painting Balsa
 

I would not worry much about the finish at this point. If the balsa is properly glued on the top and on the bottom only it will most likely snap when the LG flexes... If you grease in your landings it might not...

If it holds, then think of the finishing. I would use Balsarite applied with an old credit card, then sand and paint.

You are doing the right thing, learning by testing things...



Gerry

RE: Sealing and Painting Balsa
 

DOpe and silkspan. Or cover with a fabric, like solartex, and then paint.