Doping a frame
 

Hey gang.

I painted my first coat of Nitrate Dope on the empennage today, and I'm not sure I put a heavy enough coat on, as it seemed to disappear. When doping, do we want several light coats, or fewer heavy coats? Thanks!

RE: Doping a frame
 

Several light coats is better. The first coat usually does disappear, as you found out. But it's there, and the sealing process has started. By the third coat, you should start to see a sheen. It's sounds like you are right on track... carry forward!

RE: Doping a frame
 

Is your dope thinned 50/50?  Are you covering with cloth?

RE: Doping a frame
 

Photos!

RE: Doping a frame
 

LOL, ok soon. :D

Huck- I'm covering with Koverall, and no the dope is not thinned. Should I thin? I thought that was to happen later, when spraying.

GAP-RCU, thanks for the words of encouragement. :)

RE: Doping a frame
 

Also, what is the drying time for Sig dope? This stuff dries pretty fast, how soon can I sand and apply another coat?

Thanks [8D]

RE: Doping a frame
 

Sig dope is very thick out of the can.  I usually thin 50/50 with nitrate thinner; it goes on easier with no dragging of the brush and soaks in better.  I never use it straight from the can.  You can re-coat after as soon as dry to the touch. I use thinned Stix-it on the frame after doping when using Koverall.  Show us some pics of your plane. 

RE: Doping a frame
 

"Nitrate" thinner? I know we need to be careful with nitrate and butyrate, but I thought thinner was thinner?

RE: Doping a frame
 

Sig sell a thinner that can be used for both types. My can says - "for use with Sig supercoat, lite coat, and nitrate dope".Lite Coat is a butyrate dope; I don't know what SuperCoat is, but I think it is also butyrate. The dope can says to "thin with Sig dope thinner". I don't know what Sig says to thin butyrate dope with. I use Brodak butyrate dope for color finish and Brodak Butyrate thinner.

RE: Doping a frame
 

There was more than one request for pics... ;)

Sig 1/5 Anniversary Cub with a Saito 90TS and Robart landing gear [8D]

RE: Doping a frame
 

I will pick up some Sig thinner tomorrow and give it a whirl. Gonna need more brushes, too!



For the solid and/or sheeted parts of the frame / fuse / wings, do I dope everywhere the Koverall will come into contct with wood? Or are there places that you would ski to save weight?

RE: Doping a frame
 

I dope all balsa areas to harden it up - helps prevent denting. The dope does not add that much weight; most of the weight is the volatiles that evaporate. If you use Stix-it, or some other adhesive, you only put it on the perimeters you are covering. I am sure you know this allready. Very nice looking craft.

RE: Doping a frame
 

Yeah, hopefully someday she'll fly, heh. Gracias por la informacion

:P

RE: Doping a frame
 

If you don't dope all the wood the Koverall comes in contact with, you will end up with pin holes. The dope will be drawn through the fabric into the wood unless it has at least 2-3 coats before covering. Speaking from experience here. Also, you can reuse the brushes. I never clean my nitrate dope brush, same one used on many planes. Just let it sit in the dope for 10 minutes before using it again and it softens up.

RE: Doping a frame
 

Chances are very good that you will use quite a bit of thinner on your model. Suggestion: look up Randolph Dope on the web. There are several sources that carry it since the material is also used on full scale stuff. Aircraft Spruce is one very good supplier.

A gallon of Nitrate thinner will set you back about as much as a quart does from Sig. It's the same stuff, repackaged. Same is true for top coat butyrate dopes also.

Sage advice that is ages old: Fifty - fifty mix is typical for most brush applications, especially for surface prep and bedding of the covering. Great thing about Nitrate as a base glue, it dries very hard, quickly, with minimal weight gain. Top coats of Butyrate (Randolph, Brodak, Sig) could be used right away but if you decide on other types of top coats, wait about a week to allow full flash of the solvents. I use epoxy and polyurethane auto paints over nitrate.

A word of warningNever use any other type of top coat if you started to use butyrate tho. Butyrate continues flashing for a year or more and will pop off other paint chemistries

RE: Doping a frame
 

Cool! I just started my Sig 1/5 Cub about three days ago. I'll will also use Koverall, and the same finishing method I've used a number of times before. Perhaps you already know much of this, but just in case, here is what I do:

I use Randolph nitrate & thinner, purchased from Aircraft Spruce, then use Brodak butyrate for colors (which is re-packaged Randolph); the Sig nitrate and buty dopes work the same. First, 3-4 coats of 50/50 nitrate on all wood surfaces that will touch fabric. Light sand after the final two coats. I adhere the edges of the koverall to the wood with very thinned nitrate (70/30). The thinner melts the built-up nitrate in the wood, and sticks the fabric down. After shrinking the fabric, I then lightly fill the fabric weave with more nitrate (roughly 50/50 mix again). Filling the weave will take several coats. Don't sweat about adding weight with each coat - as others have mentioned, the clear dopes weigh next to nothing.

My first color coat is silver, which easily covers the different shades of wood, glue, & filler used during construction (these different shades can bleed through otherwise). The silver creates a uniform color base, and will easily expose any gross flaws in the finish. Now is the time to fix the flaws, so they don't show. Then I will lightly apply a coat or two of Cub Yellow, then the black lettering & lightening bolt. I can go light with the final color coats because the silver creates such a good base. Don't sand the color, yet. Next, I spray on several coats of clear buty (about 50/50). I will lightly sand (600 grit wet) only after the second or third coat of clear, otherwise it's too easy to cut through the thin color coats. I finish the model with a few more coats of thinned clear buty, with light wet sanding as needed.

With some, or all, of the clear and color coats, you may have some blushing if you are painting above 60% humidity. Blushing is white, or milky, blotches in random areas of the finish. It is caused by the humidity getting trapped in the finish as the solvents flash off. No worries, as blushing doesn't hurt anything, and is easily fixed on the very last coat of clear. With the last clear coat, add some retarder, which will slow the rate of drying, and prevent blushing. Order a small bottle of retarder from Sig when you place your final order for dopes. Usually, you don't want to add more than about 10% retarder. The best thing to do for the final coat is to wait for a day when the humidity is less than 50% (good time to call in sick to work, hehe), and with a touch of retarder, the final clear coat will come out perfect.

RE: Doping a frame
 

I'll echo what GAP-RCU said; the silver also prevents UV rays from deteriorating the fabric which, over time, causes the fabric to weaken. This is especially true when using silk or other natural fabrics. I also spray a base coat of white prior to my color coats. It provides a uniform base for the lighter and darker shades. When painting your colors, start with the light shades then go to the dark shades.

When preparing the airframe for covering, I apply a few very thin coats of Ceconite Super Seam adhesive which is designed for synthetic fabrics. When I lay out the fabric, I work out the wrinkles then activate the Super Seam with acetone.

Clean up your tools with acetone or other similar solvent. It's much cheaper than thinner!

RE: Doping a frame
 

You paint the frame until the surface is slightly glossy. Then you have enough. If not, when you apply the fabric, the wood will leach the dope into it, and you will not have the "stiction" that you really want.

Les

RE: Doping a frame
 

This is all great information, guys- thank you! [8D]

RE: Doping a frame
 

hi
been using clear dope for over 50 years on and off ,to seal balsa and install silk covering on open bays at times -only thing we had then
you can save some dollars SIG thinner is acetone and can be used with SIG butyrate and nytrate to thin it is cheaper in quart cans at LOWES and HOME DEPOT than local hobby shop
CLEAR dope is lighter than epoxy so i choose to use it in my glo fuel tank areas to fuel proof them (LIGHTER IS BETTER )
if your balsa should get fuel soaked use K 2 R dry cleaning spray to draw the fuel and oil out of the soaked balsa ,then apply a few coats of clear dope the balsa will get hard again an regain its original strength
you can use clear dope under monocoat or ultracoat wherever you choose under those film coverings to prevent glo fuel seepage into the balsa at its seams ( for ex : at the aileron seam just behind a glo engines exhaust ) the films will have no problem sticking to clear coated balsa wood,
clear dope can be used to seal any seams a film covering may have or around decals to prevent them from lifting for the long hall-,when dry it cannot be seen on the films
two or three coats will seal a balsa surface and fuel proof it -,a coat dries fast about 15 minutes-,when dry to the touch you are ready for the next coat
butyrate and nytrate have different curing rates one takes a days longer to cure and should not be top coated until the curing is complete- there will be some shrinking and drying off of solvents going on for days as per the instructions
all balsa wood surfaces must be sealed from HOT glo fuel ( with a film or a fuel proof sealer of some kind be it clear dope or SIGMENT(SIGS glue in a tube ) )to prevent glo fuel seepage into the wood-, fuel seepage will make the balsa very soft long term and cause the plane to come apart prematurely a some time in the future
i have a 20 year old -,40 size SIG UGLY STIK that has been recovered twice with monocoat-the third attemp at covering it (restoring it ) i could not get a film to stick to the surface -even after much surface prep ,i coated the balsa wood surface with SIGMENT glue and a brush-,the fuse is a natural balsa wood color now and is fuel proofed for sure
the surface came out very smooth surprisingly with no sanding-this was a last try attempt at keeping one of my most relaxed flying airplane in my fleet flyable-,still flying now with 800 plus flights it worked great for me -, it was a very last resort
the diaheadral in this top wing plane has improved the planes flying characteristics much for the better less control coupling now try it you will like it
the plane is an RC IKON in my opinion and a KEEPER after flying it for 20 years
BEST REGARDS TONY

RE: Doping a frame
 

I don't recommend using dope to fuel-proof if one is using greater than 5% nitro. You can get by with 10% nitro, if you wipe it off of the surface right away. I learned this the hard way.

Like Tony, I used dope to fuel-proof balsa & firewalls back when I was a kid. When I returned to the hobby after many years, I doped up a firewall just like I did as a kid. After twenty flights, though, I had a fuel soaked mess. That's when I figured out the nitro limits of dope (by testing). So why did it work back when I was a kid? It dawned on me that we kids could not afford fuels with greater than 5% nitro, and the hobby shop rarely stocked the high nitro stuff!

RE: Doping a frame
 

Hey guys, I more than likely need to start a new thread but, this is what i need. <div>We built a Tri-Pacer ( do not know how big) but one day it was setting on the table at our local flying field when all of a sudden.......A gust of wind came and knocked it over. There is a big gash we cut it out, made a 7 by i think.... maybe 5 inch square at the top. When we put the covering over the plane my grandfather and I, pulled it as tight as we can and we use balsarite to glue it down. There is a huge wrinkle maybe, 3 inches across. We called our friend and he said to use a heat iron or a heat gun and it should come out...... We can't get it out!!! Any suggestions? I might post some pics. If i get some taken.....</div><div>
</div>

RE: Doping a frame
 

"I don't recommend using dope to fuel-proof "

Depends on the "type" of dope. Nitrate is fuel proof/greatly resistant; butyrate is not.

"So why did it work back when I was a kid? "

Thank the EPA. The formulations have been forced to change, so that all the "good/desireable" characteristics and no longer allowed:-((((((((((((((((((

Les

RE: Doping a frame
 

Hmmm. I thought it was Butryrate dope that was "hot fuel proof".

RE: Doping a frame
 

I was also under the impression that butyrate dope was fuel proof. I just went out to the shop and looked at a few cans of Brodak butyrate dope and it says "fuel proof" right on the can.

Having used the real Stits covering on a real airplane a few years ago, I thought I would tryStits-Lite onmy latest project, a GP .60 Extra 300. I currently have all the fabric on and one coat of "Poly-Brush" on the wing and fuselage. The learning curve has been very short and shallow, and so far, I really like this process.I plan on using Poly-Tone colors and clear for the final coats - It looks like butyrate, smells like butyrate, and acts like butyrate, so I just assumed it would be fuel proof; however, I could not verify that by looking on the website or on the can. Perhaps if Chip Mull happens to catch this thread, he can comment on the various Stits products and their ability to fuel proof a structure.