Questions about dope.

I am nearing the finishing stages of my profile, and I am considering a dope finish on the fuse. (wings and tail will be film)

My previous experiences have been to buy a bottle of dope and apply it. I never put a lot of though into it. As a result you can imagine what kind of finishes I did....(I have almost always been a plastic film guy)

So, could someone please explain the difference between Butyrate and Nitrate dope- fuel proof(both?), usage, application, etc

Thanks

LAST EDITED ON Aug-16-03 AT 10:43 PM (CDT) by ()
 
Just a quick answer: Nitrate is NOT fuelproof. Some people prefer Nitrate as a base because it has more solids and is "stickier" than butyrate. You can put butyrate over nitrate but NOT vice versa. Other people just stick to butyrate alone (and then others don't use dope at all!).

Another point is that even butyrate will be attacked by high nitro (>15%) raw fuels. It is the raw fuel that really attacks most finishes. The exhaust is much tamer by comparison.

I use Nitrate on the bare wood, 50/50, for three coats. It fills the wood quicker than Butyrate. Only reason I use it. I then use thinner to apply medium silkspan to the wood, then three coats of 50/50 Butyrate followed by a fairly thick coat of Brodaks primer. I sand each coat so it is as smooth as I can get it and this also prevents a too heavy build up of dope. I tend to not put enough filler on mine, so I have never made a heavy plane with too much dope. Then again mine are not real shiney, too much time needed in flying right now. Once the filler is smooth land no grain is showing, I spray on a base of silver or gray, then sand and spray on the color coats. This is followed by several thin coats of clear. I need to put on more clear. I'm sure you well know that preparation is 80% of the job, painting is 2% and the last 18% is clean up , touch up. I use either Sig or Brodaks Nitrate. Only difference I can see is the Sig Nitrate is a little thicker and a little more tint to it. Both so far have been compatable. Little ditty: list in a verticle line. EBAN. Enamal over all, Butyrate over Acetate and Nitrate, Acetate over Nitrate, and Nitrate over nothing. A good coat or coats of Butyrate clear will help seal everthing and keep things fairly hot fuel proof, but the oil always finds its way in over time. So I've been told

Just keep it simple and don't use nitrate.

>Just keep it simple and don't use nitrate.
>
>Curt

If you run a diesel or a sparkie, nitrate is all you need. Butyrate was originally developed just prior to WW-2 because of concerns over fire resistance (nitrate goes up in a flash when on fire).
Nitrate adheres better to metal and if you use a polyester covering, then nitrate is a must to get the overcoats to adhere well to it.

You're asking about dope, fine.

But a dope finish on the fuselage, rudder, and stab should include covering it with silkspan as part of the pre-finish. Failure to do so will result in balsa grain showing through, in spite of sanding sealer/filler coats or a dozen coats of dope.

The silkspan/dope finish will add strength as well as covering the balsa grain. If you care to put the effort into the prefinish over silkspan, you can achieve an excellent result.

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"I have often regretted my speech, never my silence." -Publilius Syrus

LAST EDITED ON Aug-17-03 AT 07:52 AM (CDT)
 
Larry is right, however... If you are trying to keep things simple, just use clear dope over the wood.

Sand the bare wood smooth, then brush 3 coats unthinned, or just a little thinned clear over the bare wood. Sand it lightly with 320 just to remove the fuzz, then start adding thinner to your dope and brush a few more coats. When the wood shines, you can brush or spray your color. A coat of clear over the color will give a longer lasting and better looking finish. It can be carefully brushed, or sprayed.

If you would like a better finish, after about the 6th coat of clear over the wood, add some talc powder to the clear as filler. If you tint it with gray, you will get better results. Brush it on and sand it off until you are happy. One more coat of clear at that point and you are ready for color.

Keep in mind that lighter colors of dope do not cover well. On many colors, they look better over white or gray. White too looks better over gray. You will learn by experience.

For the best finish, Larry is on the money. Silkspan not only adds strength, but a few hours to the process.

There are alternate finishes to dope that other modelers have enjoyed success with for the type of model you are building, like Rustoleum products.

The point I wanted to make was that sanding sealers/fillers simply will not fill balsa grain well. Even multiple applications, while looking better, will "pop" the grain once the dope has cured and is exposed to sunlight.

If you do not properly deal with the balsa grain, you might as well brush on your dope finish. I know, I finished many ships like this in high school; I couldn't understand why silkspan would be necessary over a solid wood surface, nor why the grain eventually reappeared no matter how many coats of sanding sealer I had used.

I believe it was one of Ted's columns in MA where I first read that filling balsa grain was almost impossible, but it was easily covered with silkspan..

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"I know that you believe that you understood what you think I said, but I am not sure you realize that what you heard is not what I meant. " -Robert McCloskey

>The point I wanted to make was that sanding sealers/fillers
>simply will not fill balsa grain well. Even multiple
>applications, while looking better, will "pop" the grain
>once the dope has cured and is exposed to sunlight.
>
>If you do not properly deal with the balsa grain, you might
>as well brush on your dope finish. I know, I finished many
>ships like this in high school; I couldn't understand why
>silkspan would be necessary over a solid wood surface, nor
>why the grain eventually reappeared no matter how many coats
>of sanding sealer I had used.
>
>I believe it was one of Ted's columns in MA where I first
>read that filling balsa grain was almost impossible, but it
>was easily covered with silkspan..
>
>[photo not recovered: 3e69bb3870f12ad5.jpg]
>
>"I know that you believe that you understood what you think
>I said, but I am not sure you realize that what you heard is
>not what I meant. " -Robert McCloskey

It adds a tremendous amount of strength too. I usually use Jap tissue rather than silkspan over balsa, but the results are the same. You'll get a beautiful finish with far less weight and dope. I once took a Starduster X fuselage that I had covered with colored Jap tissue and clear dope (Aerogloss- actually an acrylic lacquer) and laid it across two lawn chairs and put all my weight on it just to see how strong it was. Now I'll grant you I only weighed about 125 pounds at the time (sigh!) but it neither bent nor broke... It was light too!

Thanks so much for the input guys...

I actually have more experience with Auto finishes than dope so I had considered using an auto finish over polycrylic, but I don't have my equipment near enough to work with for the next few months. (my father has it 10 hours away....).

I have successfully used a nitrate dope base covered with rustoleum and topped off with a polyurethane gloss clear many times on my all sheet half-a's, but I wanted to finish to a little higher level.

Though it will take time, I picked up 3 new sheets of silkspan from the hobby shop yesterday morning before I posted this, so I believe I will go that route.

And about preparation being 80% of the effort, I would have even made that percentage higher!

Now comes the real hard part! What color scheme to use???????

Wish me luck!