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Author Topic: Clear Butyrate Dope over colored tissue  (Read 1301 times)

Offline Mike Griffin

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Clear Butyrate Dope over colored tissue
« on: February 06, 2019, 09:07:27 AM »
I have covered an open bay wing with some yellow tissue I bought from SIG several years ago.  I applied it pretty much like silkspan by wetting it, spreading it over the wing and doping the edges down.  When it dried, it shrunk and tightened.  I want to preserve the natural translucent look of the tissue so I have brushed on one coat of clear butyrate dope to further tighten the covering.  I don't want to over dope the tissue and make it look clouded and am pleased with the look of the one coat of dope I have applied.

My question is, is the one coat adequate for fuel protection?  I really don't want to apply more dope unless it is necessary and if it is, I will but prefer not to.

Thank you in advance for the help

Mike
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Offline 944_Jim

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Re: Clear Butyrate Dope over colored tissue
« Reply #1 on: February 06, 2019, 09:41:15 AM »
Sir,

When I get home tonight I'll take pics of my 1/2A Wido Satan. It is white tissue with clear dope. Some repairs have different tissues, multiple coats of clear, others are sealed enough that the dope is barely shiny.

For best images, PM your email address. The pics should answer your questions.
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Offline Tim Wescott

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Re: Clear Butyrate Dope over colored tissue
« Reply #2 on: February 06, 2019, 09:41:47 AM »
First: that tissue should be put on dry and then shrunk.  It has a powerful shrink when put on wet (but, you haven't warped your wing, so it's OK -- right?)

Second: use multiple coats, until you're sure it's sealed.  If it's Sig and it's thinned 50-50, I'd use three or so.  It won't cloud up any more or less than if you're putting it over a normal dope finish (so avoid humidity, or use retarder), and if it does cloud you can use the techniques to un-cloud it that have been mentioned here over and over again.

If you have darker tissue you can cut markings out of that -- it ends up looking pretty good that way.
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Mike Griffin

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Re: Clear Butyrate Dope over colored tissue
« Reply #3 on: February 06, 2019, 10:25:57 AM »
Quote from: Tim Wescott on February 06, 2019, 09:41:47 AM
First: that tissue should be put on dry and then shrunk.  It has a powerful shrink when put on wet (but, you haven't warped your wing, so it's OK -- right?)

Second: use multiple coats, until you're sure it's sealed.  If it's Sig and it's thinned 50-50, I'd use three or so.  It won't cloud up any more or less than if you're putting it over a normal dope finish (so avoid humidity, or use retarder), and if it does cloud you can use the techniques to un-cloud it that have been mentioned here over and over again.

If you have darker tissue you can cut markings out of that -- it ends up looking pretty good that way.

Hey Tim,

Thank you.  This wing is for a Ringmaster 576 and applying damp did not phase the rigidity of the wing.   Humidity is not a factor and blushing has not occurred because I am doing this in a temp controlled shop in the house.   Over the years I have done a lot of models in dope but usually painted over the base dope coats.  I really liked the color of this tissue and wanted to preserve the natural color the best I could but also was concerned about fuel proofing since I am using a glow engine.

I am not sure if this tissue is even still available from SIG.  I don't think it was Japanese tissue because it is heavier than the Jap tissue I had seen in the past or maybe it was just a heavier grade of Jap tissue.  The stuff really works well and the thing I liked about damping it before applying it is that you could work all the wrinkles out of it and even the small wrinkles at the wingtips stretched out. 

I appreciate your help Tim and will proceed accordingly.

Mike
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Offline Paul Smith

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Re: Clear Butyrate Dope over colored tissue
« Reply #4 on: February 06, 2019, 11:25:19 AM »
Quote from: Mike Griffin on February 06, 2019, 09:07:27 AM
I have covered an open bay wing with some yellow tissue I bought from SIG several years ago.  I applied it pretty much like silkspan by wetting it, spreading it over the wing and doping the edges down.  When it dried, it shrunk and tightened.  I want to preserve the natural translucent look of the tissue so I have brushed on one coat of clear butyrate dope to further tighten the covering.  I don't want to over dope the tissue and make it look clouded and am pleased with the look of the one coat of dope I have applied.

My question is, is the one coat adequate for fuel protection?  I really don't want to apply more dope unless it is necessary and if it is, I will but prefer not to.

Thank you in advance for the help

Mike

NO.  One coat is NOT enough.  I would say that SIX coats might be enough.  It all depends on thinning.  Ratios like "50-50" or "3-to-1" mean nothing because we don't know the starting viscosity.

Doping is a personal technical art, not a science.  You just sort of stir the dope to feel the viscosity.  Thick dope (or paint) tends to trap solvent inside and take a long time (maybe forever) to dry.
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Offline Mike Griffin

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Re: Clear Butyrate Dope over colored tissue
« Reply #5 on: February 06, 2019, 12:08:52 PM »
Thank you Paul.

Mike
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Offline Tim Wescott

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Re: Clear Butyrate Dope over colored tissue
« Reply #6 on: February 06, 2019, 12:45:32 PM »
Quote from: Paul Smith on February 06, 2019, 11:25:19 AM
NO.  One coat is NOT enough.  I would say that SIX coats might be enough.  It all depends on thinning.  Ratios like "50-50" or "3-to-1" mean nothing because we don't know the starting viscosity.

Doping is a personal technical art, not a science.  You just sort of stir the dope to feel the viscosity.  Thick dope (or paint) tends to trap solvent inside and take a long time (maybe forever) to dry.

  • You're probably more right than me on your count of coats.  I've made a lot of 1/2-A models with tissue over wood (the same Sig tissue Mike's using -- I think they call it "plyspan", and I'm pretty sure it's an Esaki product).  I usually stop at four coats, and after hard use you can see some castor oil seeping into the finish
  • I agree about your statement about ratios, unless you're starting with fresh product of a known brand (like Sig lite-coat, which is what I was talking about).  If you're starting with a half dried out old can, or comparing Sig to Brodak or Brodak to Randolph (Brodak and Randolph are reputed to be the same brand, but the Brodak is reputed to be thinner in the can -- I've never used either, so I can't say) -- no, mixing ratios don't mean much.
  • It doesn't have to be an art.  There's a rather cheap device that all painters are encouraged to use and few actually do, called a viscosity cup.  With that and a stop watch you can actually measure the viscosity of your product, and adjust it to a specification.  Not, mind you, that I ever do -- although I recognize that I should
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Paul Smith

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Re: Clear Butyrate Dope over colored tissue
« Reply #7 on: February 06, 2019, 03:20:20 PM »
I've seen the viscosity cup in a Harry Higgley pamphlet about painting.

It would be a good tool in a big paint shop with a lot of paint.  On my scale I would waste more paint doing the tests and more thinner cleaning to the tool than it's worth.

I'm so frugal that I clean my spray gun and brushes in a CLEAN glass shot glass and put the used thinner back into the color or clear can.  It's always too thick to spray so the used thinner is a tiny step toward thin enough to spray.

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Offline Tim Wescott

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Re: Clear Butyrate Dope over colored tissue
« Reply #8 on: February 06, 2019, 06:03:08 PM »
Quote from: Paul Smith on February 06, 2019, 03:20:20 PM
... On my scale I would waste more paint doing the tests and more thinner cleaning to the tool than it's worth. ...

I would run it through the viscosity cup into my sprayer!
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AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

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