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Nitrate and Butyrate Dopes

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Old 11-16-2013, 06:40 PM
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Steve Westphal
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Default Nitrate and Butyrate Dopes

We are doing some covering with tissue and I have some questions. Is it preferable to put nitrate clear dope down first, then follow it with a butyrate color dope, or, use butyrate for all apps? Will the white glue tack down method work with nitrate dope? Any suggestions will be greatly appreciated. Thanks.
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Old 11-16-2013, 08:32 PM
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Butyrate dope will not stick to nitrate dope. Nitrate dope does not shrink. So it will not tighten your covering material. Nitrate dope is not fuel proof.

Solution: Use Butyrate tautening dope to glue your covering to the wood. Use butyrate dope to shrink your covering material. Use Butyrate non tautening dope to fill the weave of the material and for the colors.

Frank

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Old 11-16-2013, 09:06 PM
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Nitrate is available in both tautening and non-tautening formulas. It is generally used as a base preparation and for initially gluing tissue, silkspan and silk to bare balsa since it adheres somewhat better than butyrate. It can also be used as a shrink coat for fibrous or woven coverings, but tends to shrink less than butyrate. It is, as noted, not fuelproof and must be overcoated with butyrate. Nitrate does not stick to butyrate, but the converse holds.

That said, the entire process covering can be completed with butyrate (thinning improves wood penetration and eases brushing). However, when applying butyrate over a solid sheeted wing or fuselage, the high shrinkage of butyrate can cause the balsa to curl or warp. Use tautening butyrate on open areas where the covering is unsupported. Use non-tautening butyrate to protect sheeted areas or on uncovered sheet construction.

There is a short explanation on Brodak's site.

Last edited by Andrew; 11-16-2013 at 09:12 PM.
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Old 11-17-2013, 02:18 PM
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Quote:
Originally Posted by countilaw View Post
Butyrate dope will not stick to nitrate dope. Nitrate dope does not shrink. So it will not tighten your covering material. Nitrate dope is not fuel proof.

Frank
Butyrate dope doesn't stick to nitrate dope? Since when? Nitrate dope is the standard fabric base coat for full scale fabric covered aircraft, which are then sprayed with butyrate. Butyrate sticks just fine to nitrate. But nitrate over butyrate does not work well.

I find nitrate much easier to work with for adhering fabric/silk/tissue and first weave-filling coats. And it is mandatory for these jobs on polyester fabric (aka Dacron/Stits/Ceconite).

Randolph 210 is tautening nitrate dope
Randolph E4964 is (clear) non-tautening nitrate dope
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Old 11-17-2013, 03:46 PM
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OK, I got it backwards. But nitrate is not fuel proof and there lies the problem.

Frank
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Old 11-17-2013, 03:58 PM
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Steve Westphal
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So.....I think I will buy tautening butyrate to stick the tissue down and then use tautening colored butyrate for the finish. What brand do you fellas prefer....Sig or Brodak or other? 50 years ago there was simply butyrate dope!!! Thanks.
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Old 11-17-2013, 04:41 PM
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Don't use tautening for the color or you will have problems in corners. The butyrate will shrink pulling an air pocket in the corner. Areas where the stab meets the fuselage the shrinking will cause an air filled fillet. The tautening clear butyrate works best for sealing and sticking.
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Old 11-17-2013, 05:50 PM
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Steve --
If you're covering with tissue, then I'm guessing that your model is either smaller or lightly built. High shrink or tautening formulations can severely stress or warp lightly built structures and can curl balsa wood as thick as 1/8", unless applied to both sides before drying. You can use high shrink on open structures, but you really must be careful with sheeted surfaces.

SIG sells Supercoat dope in both colors and clear. The colored dope is low-shirnk, but the Supercoat clear is their high-shrink formulation. If you want non-tautening clear, then get SIG's Lite-coat clear. Both Supercoat and Lite-coat clear will stick tissue and silkspan very well. I would be inclined to use low-shrink for attaching your covering and on all solid areas. You can mix Supercoat and Lite-coat clear to lower the shrinkage factor and use that on tissue --- building a simple test frame will let you see what proportions work best for you.

Brodak dope is actually manufactured by Randolph, a major supplier in the full-scale market, however Brodak's formulation is rumored to have a higher solids content than Randolph's commercial offering which improves coverage. I generally buy my clear dopes either from Aircraft Spruce or Wick's Aircraft Supply --- online suppliers for full scale aircraft. I have used a lot of SIG's products, but have not used Brodak's --- however, many folks have been very complimentary WRT to his formulations.

As noted, high shrink dope will pull away (or bridge) from 90 degree joints and eventually will crack allowing oil to infiltrate. These bridges will have to be broken away and dissolved with thinner, then lightly coated again.
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Old 11-17-2013, 07:05 PM
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Quote:
Originally Posted by countilaw View Post
OK, I got it backwards. But nitrate is not fuel proof and there lies the problem.

Frank
Well there is that! But fine for gas or diesel.

I sure like working with it better than butyrate for tissuing open or sheeted structures, sealing tissues and fabrics, etc. It's a good base coat (or intermediary) for a variety of top coats. You'll have a hard time finding tautening nitrate through the hobby market, but it is available still as it is used for cotton/linen fabric coverings on historic aircraft. Non-tautening is used on the polyester fabrics.

Thank goodness it is so flammable, or we wouldn't have butyrate dope for models.
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