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Author Topic: Dope Compatibility?  (Read 1037 times)

Offline Andy Mutziger

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Dope Compatibility?
« on: July 13, 2018, 12:26:36 AM »
Hi All,
I'm reaching out for some forum assistance. I have a Hangar 9 PT-19 ARF that needed its noodley nose stiffened. I epoxied in maple motor mounts, epoxied ply doublers on either side, filled and sanded, brush applied 3 coats of clear Aero-Gloss dope which flowed very nicely, and sanded with 400 grit. For color, I chose a Sig dark blue buytrate dope that I thinned quite a bit because it was quite thick.

Now I have quite a mess on my hands as I painted about 1/3 of a side and the dopes are clearly not compatible - I should have stopped after the first couple of strokes! My plan is to sand the Sig dope down and maybe apply a coat of Aero-Gloss to the sanded area.

I'd sure appreciate your experienced input on where I go from here to apply a good fuel proof blue over the Aero-Gloss. FYI: I went with dope because novice me wasn't ready to apply Ultra-coat on what seemed to be complicated surfaces.

Thank you in advance for your help!
Sincerely,
Andy - Santa Margarita, CA
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Online Dave Hull

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Re: Dope Compatibility?
« Reply #1 on: July 13, 2018, 03:21:29 AM »
Andy,
Sorry to hear you are having difficulties.  I find that painting is my least favorite part of building. And reworking a plane built by someone else leaves a lot of possibilities for issues like yours.

I sure won't claim to be a good finisher, but you could consider the following:

1. Sand off the worst of the mess.
2. Solvent wipe thoroughly with lacquer thinner to remove all of the Aerogloss. Get it as squeaky clean as possible. Let it outgas a long time. I would wait a week or more. Store it in a hot garage or car even.
3. Pick a new paint system with compatible products--

   a. Since this is an ARF/Trainer, consider Rustoleum automotive primer in a spray can. Mask, spray, sand, spray, sand until you are happy. Then use a solid color Rustoleum Protective Enamel topcoat. They have more than one blue color, I believe. I have used a dark blue on one half-A plane with good results. Generally only need one application. You need to let this stuff bake a week in the heat/sun before you install engines and get fuel on it if you want some durability. You can do a search here and find more than you want to read about Rustoleum.

   b. Switch to an epoxy system for better durability. KlassKote has a two-part primer and two-part topcoats that are excellent. This will likely cost you many times more than the Rustoleum approach, and needs more safety equipment. It can be brushed pretty well, but that is a skill to be learned as well. Far better to spray if you have equipment. Again, use the search function. I have used three different blues in this product.

    c. Start over with compatible dope products. Start with SIG and end with SIG. Or, start with Brodak and end with Brodak. Or start to finish with Randolph.  Since you already have the SIG blue, it would seem your most logical path here would be to get some SIG clear and do your sealing with that. I don't think you are going to find any Aerogloss blue made in this century. If you have enough Aerogloss clear, you could buy some blue pigment....but now you are off doing experiments again. That is why in the prep steps above I suggested taking all of the Aerogloss off.

I think the KlassKote would encapsulate whatever dope you might not get removed during sanding and solvent cleaning. Probably also true of the Rustoleum. If you can't get all the Aerogloss off, then you'll know when you try to put the SIG butyrate back on. Kind of a groundhog day thing....

You might get away with Rustoleum over an Aerogloss base, but it would have to outgas a long time before I would risk trying it.

Since I have the KlassKote materials on hand, that would be my first choice. If I did not, and I wanted to save a good bit of cash, I'd go buy two cans of Rustoleum. That's going to be about $10 worth, and you will have 90% of the stuff left over for something else. My last choice would be to buy more dope and go that route. Other guys love the stuff, and they would reverse this order completely. For example, if you are not worried at all about appearance, then 5-6 coats of thinned clear butyrate followed by as many coats of color as you need to get it uniform, followed by more clear for fuel resistance and gloss protection. Decide what you will live with, because the dope guys are all expert finishers and they will go on about sanding, filling, grain filling, talc vs. whatever, exact percentages of dope to thinner as the coats progress, gas-off times, block sanding and so on. That is how they get fabulous finishes. They would not bother on a profile ARF, so keep that in mind if the conversation starts to go there.

By the way, I agree that putting iron-on coverings on a profile fuselage is just not worth it. You have to be a magician to keep the fuel and oil out--unless you put an epoxy coat on underneath, and then the covering adhesion is an issue. Or else there really is some magic involved somewhere....

Good luck!

Dave

Offline Bill Morell

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Re: Dope Compatibility?
« Reply #2 on: July 13, 2018, 07:55:06 AM »
AFAIK Aero Gloss is not compatible with ANY dope. Not really even sure it was dope.
« Last Edit: July 13, 2018, 08:28:53 AM by Bill Morell »
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Re: Dope Compatibility?
« Reply #3 on: July 13, 2018, 10:45:48 AM »
Ugh, when will Aerogloss finally disappear from the planet.
There will be a sunny day and we will fly our airplanes.

Offline Andy Mutziger

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Re: Dope Compatibility?
« Reply #4 on: July 13, 2018, 01:21:45 PM »
Hi Dave - Thank you for the great input! I'll strip it all and start over leaning toward the Rustoleum option and get on with it!

An old adage comes to mind: Measure twice (i.e. Read the forum first), cut once (i.e. one paint process per plane).

Bill, now I know!

Motorman, mine's gone! 

Thanks and happy circles! Andy
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Offline Steve Helmick

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Re: Dope Compatibility?
« Reply #5 on: July 13, 2018, 01:49:30 PM »
All things considered, I'd do what Mr. Hull suggests, but use spray can Polyurethane. More fuel proof than enamel (Rustoleum) by far. A few days and you'll be good to go. Once it's painted, it'd still be a good idea to cook it in the car for a day or two.  H^^ Steve
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Offline Dan McEntee

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Re: Dope Compatibility?
« Reply #6 on: July 13, 2018, 04:28:08 PM »
   I had learned that you could put Aerogloss over anything, but you couldn't put ANYTHING OVER Aerogloss. Sticking with one product all the way through is the best option. Some guys are having good luck wit just putting a thin coat of two part clear over the nose and along the wing roots, where raw fuel could be spilled. Charlie Reeves did a great job with this on his Humbler. That makes repairs a bit easier if necessary. I plan on trying the Nasson system if I ever get a new plane built up and finished!  HB~> HB~>
  Type at you later,
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Online Dave Hull

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Re: Dope Compatibility?
« Reply #7 on: July 13, 2018, 07:15:56 PM »
Steve,
Which specific polyurethane are you recommending? I have tried a couple different ones on "practice planes" and neither worked out as well as I had hoped. Which brand and type are you recommending for improved durability compared to the Rustoleum?

Dave

Offline Steve Helmick

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Re: Dope Compatibility?
« Reply #8 on: July 14, 2018, 12:13:20 PM »
The last polyurethane I used was "Formula U", which was a model airplane specific product. It may have been a Pactra product, which then became Midwest, and then went away. It was nice stuff and bulletproof on my "Baster" NW Sport Racer. "Baster" = Faster/Buster. But I don't think I used more than 12% Vitamin N. It came out smooth, but dust can be a problem, because polyurethanes usually don't dry super fast. 

Folks here on SH have often said that Varathane clear polyurethane is fuelproof but yellows with age. I'd expect the same durability from colored Varathane spray bombs, but I have no idea if they have a suitable color for the OP's project...if that even matters at this point in the repair project. I'd read the label very carefully before purchase, but that's what I'd plan to use.   H^^ Steve
In 1944 18-20 year old's stormed beaches, and parachuted behind enemy lines to almost certain death.

In 2015 18-20 year old's need safe zones so people don't hurt their feelings.

"Be polite, be professional, but have a plan to kill everybody you meet." General Mattis.

Offline Randy Cuberly

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Re: Dope Compatibility?
« Reply #9 on: July 14, 2018, 12:21:17 PM »
I think good Ole' Butyrate DOPE is tough to beat and is easy to use and repair.  Unfortunately even it has become pretty expensive of late, especially the thinner!

Dupont "Chroma Color" and "Chroma Clear" are easy to use and give a fantastic finish albeit very expensive.  It goes over Butyrate dope very nicely.  Not so easy to repair however...at least that's what I've been told.

I'm doing a "Whitely Shoestring" with it now.  Great colors.  John Callentine used it on his "Thunder Gazer" and it was gorgeous!

Bob Hunt used it extensively on several airplanes!

Randy Cuberly
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Online Dave Hull

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Re: Dope Compatibility?
« Reply #10 on: July 14, 2018, 12:45:37 PM »
Steve,

Hmmm. I guess I need to check my used paints stash to verify brands. I believe I tried the Varathane spray--I used it on propellers as a test--and was not impressed by the fuel resistance. I also tried one of the modeling-specific clear urethane topcoats. It was kind of marginal. Last year I refinished a Quicky Rat (10% Nitro Class) that was gumming and peeling. I completely stripped the urethane and  put KlassKote on it and don't expect to have any durability issues.

Dave

Offline Randy Cuberly

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Re: Dope Compatibility?
« Reply #11 on: July 14, 2018, 01:14:51 PM »
I don't think anything that comes out of a "rattle" can is going to hold up to fuel very well!
At least that's been my experience over the years!  The Top Flite Stuff os very fuel proof but hardens after a short time and develops cracks in the surface of the paint!

Everything else I've tried either becomes sticky with fuel residue or actually runs off on the ground with raw glow fuel! 

The Automotive two part clear coats are bullet proof and will go over just about anything, but are a real pain when it comes to repairs!  Nothing else wants to stick!!

Randy Cuberly
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Offline Andy Mutziger

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Re: Dope Compatibility?
« Reply #12 on: July 14, 2018, 03:08:32 PM »
Hi All and thank you kindly for the great input. I'm getting some stripper today. It is sounding like brand consistent dope or two part epoxy paints may be my best solution. Reading on the Klass Kote page, it sounds like I could paint with several options and use their clear for nitro protection. It is a trainer, so I am open to rattle can options if there is consensus from forum folk on an option that works decently. I'll do some searching in the back posts. Cheers and thanks a million!
Andy
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Offline Brett Buck

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Re: Dope Compatibility?
« Reply #13 on: July 14, 2018, 04:11:50 PM »
I don't think anything that comes out of a "rattle" can is going to hold up to fuel very well!\
The Automotive two part clear coats are bullet proof and will go over just about anything, but are a real pain when it comes to repairs!  Nothing else wants to stick!!

   Thats what everyone says, but I have made *massive*1 repairs on my airplane, and never had even a hint of a problem with adhesion. I use 2-part epoxy with car clear, I more-or-less sand off what needs it and paint over it, never had an issue with it. Almost anything sticks better than dope, which sometimes doesn't even stick to itself.

    Brett

1 complete refinished fuselage twice, repaired fuse bottom, repaired stabilizer, painted over divots, put more clear over sand-throughs, never an issue or adhesion issue, or fish-eyes. Color-matching issues, thats another story.


Offline Brett Buck

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Re: Dope Compatibility?
« Reply #14 on: July 14, 2018, 04:17:48 PM »
Hi All and thank you kindly for the great input. I'm getting some stripper today. It is sounding like brand consistent dope or two part epoxy paints may be my best solution. Reading on the Klass Kote page, it sounds like I could paint with several options and use their clear for nitro protection. It is a trainer, so I am open to rattle can options if there is consensus from forum folk on an option that works decently. I'll do some searching in the back posts. Cheers and thanks a million!
Andy

  Instead of stripper, try a 50/50 mix of acetone and lacquer thinner, applied with steel wool like a wash. Do it outside in a wind because it is a very heady mix and be very careful about ignition sources. I was put on to this by my old radio restoration buddies, it's almost miraculous and leaves nothing behind, which is a big issue with chemical stripper on bare wood. It's also cheap. If you have a problem, replace the lacquer thinner with dope thinner (which is no so cheap).

     Brett

Offline Randy Cuberly

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Re: Dope Compatibility?
« Reply #15 on: July 14, 2018, 07:00:04 PM »
  Instead of stripper, try a 50/50 mix of acetone and lacquer thinner, applied with steel wool like a wash. Do it outside in a wind because it is a very heady mix and be very careful about ignition sources. I was put on to this by my old radio restoration buddies, it's almost miraculous and leaves nothing behind, which is a big issue with chemical stripper on bare wood. It's also cheap. If you have a problem, replace the lacquer thinner with dope thinner (which is no so cheap).

     Brett

Well I can easily believe you don't have a problem with adhesion after using that mix, but what about the adjacent areas where you don't want to remove everything?

Randy Cuberly
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Offline Bill Morell

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Re: Dope Compatibility?
« Reply #16 on: July 14, 2018, 10:08:43 PM »
I took Larry Fernandez's advice and tried Klean Strip Lacquer Thinner from Home Depot. as long as it says Max VOC on the back. I can't tell any difference from Aircraft Spruce thinner and is much cheaper. $18 a gal. here in So. Ca.
Bill Morell

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Online Dave Hull

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Re: Dope Compatibility?
« Reply #17 on: July 14, 2018, 10:12:59 PM »
Don't use stripper! That just adds another chemical residue to the problem. Lacquer thinner works good. I will have to try Brett's tip on the next OPP job (Other People's Plane restoration job). If it more easily/completely pulls old finish out of the grain, then that would be a winner!

I have a few "un-favorite" chemical stripper stories. My least favorite one involved driving with a friend out to a SoCal airport. He had saved up enough cash to get his Cessna 172 painted. The paint shop flew the plane over to another airport with the facilities to do the paint stripping. They had a concrete pad with a center drain/collector, if I recall correctly. Unfortunately, they applied the stripper and let it sit, but didn't notice that it was collecting around the main landing gear fuselage penetration. They did not get this cleaned off and the result was that it attacked the steel gear leg, which probably already had some corrosion issues. The weight of the plane on the gear and the extended exposure to the stripper induced stress corrosion cracking. The gear leg failed, the plane fell on the ground, and the wing, tail, and fuselage were severely bent. It was not a happy situation, as you can imagine. We shouldn't let a bit of a paint problem with a model airplane cause a huge amount of mental stress!

Offline Andy Mutziger

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Re: Dope Compatibility?
« Reply #18 on: July 14, 2018, 10:50:59 PM »
Perfect, thank you guys for the additional input!! Lacquer thinner it is and I'll have acetone on deck to add to the mix just in case!
I'll post results - Cheers!
Andy

PS - Wow Dave! That's quite a story. Did your friend get resolution and did the plane get back in the air?
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Online Dave Hull

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Re: Dope Compatibility?
« Reply #19 on: July 14, 2018, 11:46:07 PM »
I believe that the Cessna was eventually repaired. New right wing assembly, new horizontal stabilizer and elevator. Not sure how they repaired the damage to the rear fuselage. It was torsionally deformed when the stab hit the ground and the wing was still falling....  And of course, they had to install a new main gear strut. Imagine you were the mechanic that saw the plane laying on the ground when you arrived at work. And what exactly do you tell the boss?

Good luck with your refinishing job. It should go fine. No need to make it hard.....

Dave

PS--I hope to fly my "new" airplane at our picnic tomorrow. I was a gifted full fuse job done up in Rustoleum. It had some serious engine/tank geometry issues, so I essentially grafted a new nose onto it. There was no reason to attempt to refinish the whole plane since it was new/unflown, so the only real choice was to match what was there. Off to the store for some Rustoleum Red. The refinishing went fine and looks at least as good as it did before the surgery. Now I will get to see if the tank will feed like a stunt ship instead of a straight-and-level-only plane. No way I want to cut into it again....


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