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Author Topic: Dope.  (Read 1139 times)

Offline kevin king

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Dope.
« on: January 11, 2023, 10:33:55 PM »
If my goal is to have a light, buffed out mirror finish, everything must be kept flat from the wood surface up. That Is why i am considering spraying a coat of clear before applying silkspan instead of brushing on a coat of clear just prior to laying down the silkspan. Would like your feedback on this, Thanks

Kevin

Offline Tim Wescott

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Re: Dope.
« Reply #1 on: January 11, 2023, 11:08:26 PM »
At that stage of prep, the wood grain dominates.  In fact, the first coat of dope raises the grain and hardens it, so the wood will feel considerably rougher after the dope dries than before you put it on.  I put on somewhere around four coats of clear -- sanding in between coats -- before the 'span goes on.

There's really not much advantage to spraying on the dope until you've got most of the silkspan grain filled -- before that, it takes a slightly longer time and a lot less thinner to brush the dope on.  (If I were doing two planes at once or had a no-prep paint booth this calculation would be different).
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Offline kevin king

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Re: Dope.
« Reply #2 on: January 11, 2023, 11:49:37 PM »
Thanks Tim. So what your saying is you brush on 4 coats sanding in between coats, and do you brush on another coat and then apply the silkspan immediately after, while the dope is still wet?

Offline doug coursey

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Re: Dope.
« Reply #3 on: January 12, 2023, 09:07:49 AM »
THIN THE DOPE 75% FOR THE FIRST FEW COATS THEN A FINAL THICKER COAT......YOU WANT IT TO SOAK INTO THE WOOD SO THE COVERING WILL BOND GOOD
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Offline 944_Jim

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Re: Dope.
« Reply #4 on: January 12, 2023, 09:54:23 AM »
Hi Kevin,

I hope this submittal is still relevant...I began typing it a few hours ago. :o

Spraying the bare frame will incur the weight penalty of dope being where it does your covering no good. By the time you spray/seal ALL the wood, and prepped only covering contact surfaces, you will have sprayed a lot more frame than necessary.  Brushing it on gets it where it only where it needs to be...rib edges, TE/LE, any balsa sheet surface you plan on covering...

Four coats sounds about right. Since the wood grain does rise (yet, less and less each time you seal) I do two thinned coats to get deep into the fibers, then go back to straight dope as I fill, remove grain, seal slick (to my satisfaction...but I'm not looking for show quality).

If the frame is sealed, slick and shiny (or close enough for my satisfaction) then I begin tissuing. Wetting the perimeter of the panel with thinned dope will "melt" the sealed surface so the (in my case, wetted tissue) material will stick to the base coat. This is just a quick wetting to stay wet long enough to lay the material. More thinned dope is applied through the just-laid material at the contact edges to soak into and through the material to the base coat. Bonus...if your wetting dope is thinned "just right," is that it almost floats the material long enough to tug the wrinkles out. This is akin (close, but not quite) to floating window tint on glass before squeegeeing it down. Once "glued down," I like to make another pass to ensure edges are secure.

Any of the later methods of securing covering start with a sealed frame...regardless of sealing and adhering compounds used. I'm thinking of the gluestick or ModgePodge users in particular here. I can't think of any way to stick any covering to bare, sanded smooth wood.

PS I dig your builds!
« Last Edit: January 13, 2023, 04:17:14 PM by 944_Jim »

Offline kevin king

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Re: Dope.
« Reply #5 on: January 12, 2023, 11:02:44 AM »
Hi all. I think i may have to adjust my question.

Offline kevin king

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Re: Dope.
« Reply #6 on: January 12, 2023, 11:11:37 AM »
To clarify my question, I have  3 coats brushed on the raw wood, (flaps, elevators) and its sanded with 320 and perfectly flat. Next i sprayed on 2 coats of clear and it it looks great,  my concern is brushing on a coat at this point  would ruin the flat surface. It would be the same if you had a buffed out airplane and then brushed a coat of dope on it. This is the reason i think spraying a coat of clear before silkspan would result in a flatter lighter surface before applying the silkspan would be better than applying silkspan to a wet, wavey brushed surface. Apologies for not being more clear in my question.     
« Last Edit: January 12, 2023, 11:42:18 AM by kevin king »

Offline kevin king

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Re: Dope.
« Reply #7 on: January 12, 2023, 11:37:39 AM »
So to clarify, at this point i have a 3 brushed on coats on the raw wood, (flaps & elevators) of 70/30 dope, and its block sanded dead flat with 320.  Next i sprayed on 2 coats of the same mix and the part looks great. The next step is to apply silkspan.  Most people including myself would then brush on a coat of clear and apply the silkspan. This is where i am thinking to deviate. Some may think i am over thinking this, and yes they are probably right. But my thoughts were to spray a 3rd coat let it dry to the touch, then apply the silkspan and brush 3 more coats.  The idea is the sprayed coat will still be fresh enough to bond to the next coat while at the same time will still remain as a flat surface, As opposed to a wavey wet brushed coat that will float around, shrink and what not, if that makes sense?
« Last Edit: January 12, 2023, 11:59:11 AM by kevin king »

Offline 944_Jim

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Re: Dope.
« Reply #8 on: January 12, 2023, 12:01:26 PM »
On 1/2A, I'd leave smooth, sealed wood as is, and continue with my art work. The times I've  tissued solid/smooth/sealed surfaces, no brush marks came through the tissue. Now what happens on top of the tissue comes back to your fill/seal process just as I't does on the wood.

May I ask why you want to cover the solid wood surfaces? If they are sealed, smooth, and visually pleasing, I'd skip the covering. Or is this model large enough that you want the covering as a strengthener? If so, the covering will also require surface smoothing efforts as well.

I think your idea of spraying a wetting/setting/sticking coat may be of value, if for no other reason than the ability to wet the entire surface quickly, and then apply the covering quickly. Thinned dope should flow/level pretty well regardless of how applied, but brushing could take long enough to disrupt the process as it begins to set on the first laid parts. Getting your covering sized appropriately when dry will make this a bit easier. Just be sure to do on one side as quickly as possible to the other side...or enjoy your Pringles. LL~

I'd love to know what your are working on at this point.

Offline 944_Jim

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Re: Dope.
« Reply #9 on: January 12, 2023, 12:23:58 PM »
Oh, and this may be a good time to run a test piece with alternate adhesives.

Thinking out loud (admittedly, I'm no expert using any of this), but I'd be curious to see how the covering adheres to your smooth wood using a gluestick, or thinned white glue...or any of the other ways people stick their covering down. I understand the gluestick crowd says an iron helps "wet" or melt the gluestick to stick the covering hard to the wood...kind of like an "apply dry Stix-it." I did mention I'm thinking out loud.

Online Brett Buck

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Re: Dope.
« Reply #10 on: January 12, 2023, 12:28:01 PM »
To clarify my question, I have  3 coats brushed on the raw wood, (flaps, elevators) and its sanded with 320 and perfectly flat. Next i sprayed on 2 coats of clear and it it looks great,  my concern is brushing on a coat at this point  would ruin the flat surface. It would be the same if you had a buffed out airplane and then brushed a coat of dope on it. This is the reason i think spraying a coat of clear before silkspan would result in a flatter lighter surface before applying the silkspan would be better than applying silkspan to a wet, wavey brushed surface. Apologies for not being more clear in my question.     

    So, there is nothing on the wood but dope to stabilize the wood? Like thinned out epoxy?

    I am far from an expert on dope finishing, but normally you want at least silkspan and dope as soon as you can stick it down to stabilize the wood and provide a consistent underlying surface. With all that dope film thickness, I would worry about it all shrinking and making it impossible to flatten out.

             Brett

Offline kevin king

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Re: Dope.
« Reply #11 on: January 13, 2023, 12:40:02 AM »
Quote from: 944_Jim link=topic=62975.msg650106#msg650106 date=1673550

I'd love to know what your are working on at this point.
[/quote
Its a Vector 40 Jim. i always silkspan everything, It adds alot of strength and not alot of weight, and it helps hides the woodgrain.

Offline kevin king

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Re: Dope.
« Reply #12 on: January 13, 2023, 01:30:43 PM »
Has anyone tried attaching the silkspan by brushing on thinner? Pro's and cons? Ive heard of this but never tried it

Offline Jim Svitko

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Re: Dope.
« Reply #13 on: January 13, 2023, 01:42:01 PM »
I have always brushed clear dope, thinned 50-50, to attach silkspan.  I never tried only thinner.  I am not sure if that would sufficiently "melt" the dope you put on the bare wood first and still get the silkspan to stick very well.

You might just drive the previous coats of dope deeper into the wood and leave nothing at the surface for a bond.

Offline 944_Jim

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Re: Dope.
« Reply #14 on: January 13, 2023, 04:14:25 PM »
Yeah, what Mr. Jim said...
I seem to remember trying that on my Stuntman 23 (back in 1983...so give my brain a break, please). I doped the whole plane to seal the wood, and papered the wing, stab and rudder for strengthening. I also want to be clear that I tend to build too heavy, and have learned what little I know from first hand, old school trial and error. I had no peers to experiment with, nor a mentor to show/teach/guide me. So this means that what I "know" may not be optimal, and quite possibly just mis-informed belief. Oh, and I build/fly 1/2A...in short, when I begin my Brodak Cub, or my Veco Tom Tom, I may be re-thinking the same questions...

What I learned was that thinner-only would quickly saturate the tissue, and begin to flash off in different places before really affecting underlying dope and not sticking the tissue down very well. The tissue felt like an old, dry scab ready to fall off the injury. My recollection is that whatever stuck wasn't enough to keep the tissue down firm, and the tissue skinned-over enough that any more dope couldn't get through the tissue and below. In fact , the tissue would almost "de-laminate" if worked harder.

Using thinned dope allows for saturating the tissue and keeping it wet long enough to soften underlying dope for a really good, firm stick, with dope throughout the tissue grain and below. Subsequent dope applied much like in the late stages of sealing balsa would behave much like we expect it to go.

Offline kenneth cook

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Re: Dope.
« Reply #15 on: January 13, 2023, 06:53:11 PM »
             Kevin, your finishes are very high quality. I agree with your logic. I always sand in between coats but using Polyspan lately, I have to tell myself not to touch it.The Polyspan at least for me is taking roughly 5-6 brush coats of thinned dope.  One thing I've been doing is adding retarder to my last brush coat of clear prior to spraying. This really offers a nice smooth base as it levels everything off.

       

Online Steve Berry

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Re: Dope.
« Reply #16 on: January 15, 2023, 09:36:08 AM »
I may be in the minority here, but for a dope finish, I would simply follow what Windy or Sparky do.

3-4 unthinned coats of dope on the raw frame, sanding in between. Then a 50/50 thinned coat, apply wetted silkspan, a brush it down, rubbing with fingers as needed to achieve good adhesion.

After that's dry, brush with 3-4 more coats, sanding in between, eliminating any wrinkles that didn't get pulled out at first (sand them off). By the time it's all finished, the surface should have a sheen to it - not glossy, but no "dry" spots, either.

When in doubt, start watching some of Windy's or Sparky's videos and follow along.

That's what would do, especially since they both have won concours awards (Windy multiple times).

Steve

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« Last Edit: February 05, 2023, 11:34:47 AM by Steve Berry »

Offline Dave Moritz

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Re: Dope.
« Reply #17 on: February 01, 2023, 12:56:38 PM »
Steve:

Many thanks for watching and summarizing the videos in so few words - that is a dedication to the hobby and a skill in itself! The narrative I've been waiting for!

Dave Mo...
It’s a very strange world we live in, Master Jack.” (4 Jacks and a Jill)

Offline Tim Wescott

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Re: Dope.
« Reply #18 on: February 18, 2023, 03:06:11 PM »
Has anyone tried attaching the silkspan by brushing on thinner? Pro's and cons? Ive heard of this but never tried it

It seems to work well for silkspan and for "domestic" tissue (i.e., the crap that comes Comet kits).  Don't bother trying it with Esaki or equivalent "good" tissue -- that stuff doesn't let the thinner through; you don't get a good bond.  I get a better bond using dope, and rubbing it in, or (gasp) putting the silkspan onto wet dope.  If you're going to put silkspan onto wet dope you have to do no more than six inches at a time; when I do this I usually end up going over the top and rubbing to really get the attachment right.
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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