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Author Topic: Brodak Dope  (Read 389 times)
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qrashandburn
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« on: September 22, 2020, 11:18:09 AM »

This year I've ventured into using dope to finish my planes instead of just krylon after tautening.  I started with EZE-dope which did a very good job of tightening the tissue and left a nice, althogh blotchy harder finish.  I'm currently trying out brodak nitrate dope and I'm unsure of what my expectations should be.  I'm using a 50/50 mix with brodak thinner after tautening with water.  The coats go on pretty thin and dry incredibly rapidly, within minutes.  I was under the impression that it takes hours for a coat of dope to dry.  The tissue doesn't seem to be all that much stronger, even after a few coats and it's not that glossy either.  I'm wondering if this is all typical of nitrate dope or if anyone has experience with Brodak nitrate in particular.
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mick66
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« Reply #1 on: September 25, 2020, 02:21:19 AM »

Hi

What size model and what tissue is it and is it shrinking or non shrinking dope. 

On say an outdoor sport FF model with light Esaki tissue I'd expect to water shrink followed by 2 coats on 30% shrink and then maybe 4 coats of 30% non shrink.  That's personal preference and 4 or 6 coats of 30% shrink would be good enough for me.

It dries very quickly but will continue to 'shrink' for days or weeks to come.

Cheers

Mike

Ps I often use BananaOil on the final coats and tend to do tissue over Mylar these days ... much tougher for not much more weight
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packardpursuit
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« Reply #2 on: November 17, 2020, 04:30:24 PM »

Two coats of Nitrate dope(50-50% dope thinner w/ 8-10 drops of castor oil per 8 oz of mixture) is my usual finsh for light rubber ships, Peanut scale etc.  Larger models need and can carry more coats of same dope mixture. The more coats, the shinier the finish gets. For rubber enduraance types, such as gollywock/'winter Cup"/ wakefield and unlimited types/ even A-1 glider, get  five coats, the finish is pretty shiney, at this stage.  Castor, or other veg oil, added is to "plastisize the dope". I prefer  Johoba oil. as it it seems to  diksolve more readily than castpr. There are also chemical additives from  better paint outlets, that do the same thing. What you want are "flex agents" for traditional Lacquer finishes.

I can see no advantage to buying/using "non-taughtening"  dopes, as the traditional "plastisizers" for full scale work are exactly the same for models!   I've got a 1930's Mechanic's  text book that calls out the very same ingrediences for dope work. There are lots of horror stories about Butyrate dope but I find the two types interchangable as far as actual working properties, sealing, and shrinkage go.  Problems  with structural damage by over shrinckage of tissue is usully the fault/haste  of the builder ,not taking proper PRECAUTIONS in the build and follow-up with careful attention warp reduction covering practices.   Again, same as full scale!

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