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Author Topic: Use of polyester finishing resin over balsa  (Read 2294 times)

Offline David Ruff

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Use of polyester finishing resin over balsa
« on: February 27, 2018, 05:57:38 AM »
I have been reading a Harry Higley book titled "No Secrets" and he swears by applying a coat of polyester finishing resin over all balsa as the first step in finishing.
Anybody here using that technique?

Tom Morris just applies three coats of nitrate.

Opinions?
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Offline David Ruff

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Re: Use of polyester finishing resin over balsa
« Reply #1 on: February 27, 2018, 06:04:11 AM »
Well, now that I read more about this, I will go with nitrate. 
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Offline Avaiojet

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Re: Use of polyester finishing resin over balsa
« Reply #2 on: February 27, 2018, 07:26:19 AM »
David,

We used to use polyester resin on all our R/C pattern ships, for 20 or better years.

Thing is, the first reduced coat is just the base before you apply glass cloth.

There's other steps that follow before primer.

Here's an award winning model I did using polyester resin and glass cloth.  ;D

Auto primer, auto base color, Don's brushing lacquers, One-Shot sign painter's enamel, hand applied 23K gold leaf finished with Dupont clear. Early 80's.  LL~ LL~ LL~

Done correctly you get so little orange peel.

Guys back then were using K&B. So, instead of using K&B paint, which I never liked, I used auto paint systems only because of my background having used them professionally.

If I had body shop accounts today and access to a spray booth, I would still be using that system.

I have never used nitrate on any of my models.



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Offline Dan McEntee

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Re: Use of polyester finishing resin over balsa
« Reply #3 on: February 27, 2018, 05:42:24 PM »
  Hi David;
     The main reason you don't want to do any of what Avaiojet just laid on you can be said in one word  H E A V Y!!!!! It may be fine for hanger queens and airplanes that won't get flown. It has no bearing on use for a control line stunt model. If you want to glass a wing center section for strength? Yes, but not to the finish point. If you want to re-enforce the nose/tank/engine compartment? Yes but not to the finish point of the process. It would all get sanded as smooth as possible , then filled in with coasts of sanding sealer and dope and then endless sanding. You can do the nitrate if you have it, or even just use butyrate all the way through. If you start with nitrate, give the base coats time to gas off before proceeding. Nitrate has been used in the past as the first build up coats because it was felt that it had better adhesion properties and filled a bit better, but it is NOT fuel proof. Some times guys get it mixed up in their shop and some accidents happen that need to be sanded back off. That is why some use butyrate all the way through. Seeing as you answered your own post, I think you may have figured out most of this on your own. When finishing with dope, search out anything on the finishing section written by Bill Byles or Larry Fernandez on the subject and you will get the straight scoop.
  Type at you later,
   Dan McEntee
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Offline Steve Helmick

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Re: Use of polyester finishing resin over balsa
« Reply #4 on: March 03, 2018, 01:39:04 PM »
Way back in the middle '60's, I used polyester resin for base coat on my speed models, and for fiberglassing the nose fairing of combat models. It worked fairly well, but the more I used it, the less I liked it. For one, shelf life is maybe a year, and you never know how long it was on the shelf. It's also very flammable and odiferous, but what do we use that isn't? Pot life is also short. There were also times when it didn't get really hard, which is no Bueno. I'd much rather use Zpoxy finishing resin for all finishing tasks, with two or three coats of thin Nitrate dope under it.  H^^ Steve
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Offline Serge_Krauss

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Re: Use of polyester finishing resin over balsa
« Reply #5 on: March 04, 2018, 02:32:30 PM »
FWIW: I have produced model fuselages and tails with .56-oz fiberglass applied with West Systems epoxy that are lighter than doped-on silkspan, when then finished with colored and clear butyrate dope. I think that's because of the glass not being allowed to float and needing only a small amount of epoxy in its weave. I built two horizontal tails of almost equal area and compared the weights. The plane below is several ounces lighter than the original P-Force on which it was based and which was all doped-on silkspan.
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Online Tim Wescott

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Re: Use of polyester finishing resin over balsa
« Reply #6 on: March 04, 2018, 03:47:17 PM »
Quote from: Serge_Krauss on March 04, 2018, 02:32:30 PM
FWIW: I have produced model fuselages and tails with .56-oz fiberglass applied with West Systems epoxy that are lighter than doped-on silkspan, when then finished with colored and clear butyrate dope. I think that's because of the glass not being allowed to float and needing only a small amount of epoxy in its weave. I built two horizontal tails of almost equal area and compared the weights. The plane below is several ounces lighter than the original P-Force on which it was based and which was all doped-on silkspan.

I think epoxy is superior in every way except for cost and perhaps toxicity (and I'm not sure about toxicity).

It'd be interesting to see what you could do with vacuum-bagging fiberglass cloth onto a fuselage, if you could figure out how to do it so you're not making big wows in between the fuselage formers.  (I'm thinking bagging it inside and out, which means lots of messing around and probably wasted time perfecting the process compared to just using silkspan and dope).
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Offline David Ruff

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Re: Use of polyester finishing resin over balsa
« Reply #7 on: March 08, 2018, 09:42:18 AM »
I know my friend uses thinned dope to apply light fiberglass cloth to balsa surfaces.  Works real well.  So you have the glass cloth but no epoxy weight.

 :!
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Offline Serge_Krauss

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Re: Use of polyester finishing resin over balsa
« Reply #8 on: March 08, 2018, 06:27:24 PM »
Three disadvantages go with two "advantages" of doped fiberglass.

Disadvantages

1) The dope continues to shrink, revealing the weave.
2) Doped-on fiberglass is too elastic, if you care about stiffening a fuselage, for instance (use biased weave).
3) The dope tends to liquefy with subsequent coats, thus floating the glass and using more dope.

Advantages:

1) The dope can be applied very easily, especially by pre-coating and then applying the glass with thinner. This makes mild compound curves easy.
2) Dope is much less messy than resin, especially when you don't take care and plan ahead in resin application.

The end product with resin is better, but labor is more difficult. As I posted; you can create a lighter structure with epoxy.

Perhaps an advantage: You don't need to rough and clean the doped undercoats so much to ensure that final butyrate coats adhere.

SK
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