Hi,

Living in Europe I use nitro dope rather than butyrate dope to finish my models. I spray on a last thin coat of clear epoxy because as everybody knows nitro dope is not fuelproof.
I have been watching Windy Urtnowsky's fantastic videos for a while and would like to try butyrate dope. But my question is: to what extent is butyrate dope fuelproof (to what nitro content)?

Thanks,
Paul

The bottom line is raw fuel will eat into a dope finish fairly quickly. But if you have enough clear on it, especially around the nose area, it's pretty durable. You just need to be a bit careful with filling the tank and priming the engine with raw fuel. Exhausted fuel doesn't seem to hurt it. An all dope finish lasts for years and is much easier to repair than a dope finish with epoxy or automotive clear coat.

Brodak dope, from what I heard, is made by Randolph.  Both nitrate and butyrate can be bought under the Brodak or Randolph hame.  A few months ago I heard that Certified bought Randolph but I have not been able to confirm that.

The Brodak formulation might be a bit different from the Randolph/Certified product but they are compatible.  I have used Randolph butyrate thinner with Brodak dope, and vice versa, with no problems.  I have applied one over the other with no problems.  This goes for clear as well as colors.  Much cheaper to buy Randolph thinner and use it with Brodak dope.

The Brodak Crystal Clear does not appear to have much, if any, fuel resistance.  I have planes with dull blemishes on them where raw fuel made contact.  Although I like the fact that it is "crystal clear" and might not yellow as much over time, its fuel resistance is minimal.  From the quick and dirty experiments I did, the Randolph non-tautening clear appears to have more fuel resistance than the Brodak Crystal Clear.  Not that it is fuel proof, just a bit more resistant than the Brodak clear.

Ok so I want to make a vintage combat plane, and just clear the wood, and SLC or Fascal on the wings. Can I just use butyrate dope after the wood prep? Or does it need something over the butyrate? I've seen many many "clear" combat planes. What's the trick?

Back in the day, I used colored silk for my combat planes.   Glass cloth and epoxy around the nose and dope on the rest.   I used clear dope until it kind of a sheen to it.   Never a problem with the fuel available back then.  Of course 10% nitro is all I used. 

Of course there was always a pin hole or several that let fuel in.