Dope is lifting

[Dan Berry]

OK, I'm having a recurrent problem and now it sorta matters.

I am using SIG dope-clear and white. It is lifting on the inside of corners/fillets.
I am using DuPont Acrylic Lacquer thinner as a solvent. It is a brushed finish.
I have also noticed the problem on some Free Flight fuselages but it isn't such a concern there.

Am I too thick? Too thin? Too dumb?
I do not recall having the problem with some Brodak clear or color.

Anyone got any ideas to help me make my Ringmaster attractive?

TIA
Dan

[Larry Fernandez]

My first question is, what material are you using for your fillets?

Larry, Butttafucco Stunt Team

[RC Storick]

It's lifting because of shrinkage. Don't paint the fillets. Easy to do when spraying but hard to do when brushing. Light dry coats on fillets.

[Dan Berry]

The fillet is just epoxy and microballoons.
It also does it on a simple 90` joint.
It's a sometimes thing, not always along the length of a joint.

I know that it's shrinkage but I also had the problem with the SIG LiteCote.

[billbyles]

OK, I'm having a recurrent problem and now it sorta matters.

I am using SIG dope-clear and white. It is lifting on the inside of corners/fillets.
I am using DuPont Acrylic Lacquer thinner as a solvent. It is a brushed finish.
I have also noticed the problem on some Free Flight fuselages but it isn't such a concern there.

Am I too thick? Too thin? Too dumb?
I do not recall having the problem with some Brodak clear or color.

Anyone got any ideas to help me make my Ringmaster attractive?

TIA
Dan

Hi Dan,

You are encountering a common problem when working with the materials you are using.  The problem, as Robert noted, is too much dope in the fillet areas.

The brand of dope you use has no effect on the problem, whether it be Brodak, Sig, Randolph, or Certified brand.  The initial coats of dope (after covering) should be tautening type butyrate applied with a brush, only over the open bay areas - about three coats thinned about 30 to 40 percent thinner/dope. 

Subsequent coats of dope can be brushed on (Jim Kraft, I think, is very successful with brushed finishes) using only non-tautening type dope such as Sig Light-Coat or Randolph non-tautening clear.  All Sig and Randolph colors are the non-tautening type, although Sig's label on colors says "Super-Coat".  For all coats after the first three on the open bays I recommend the use of additional plasticizer (I use Dave Brown's "Flex-All") in the amount recommended on the bottle.

Also, using Du Pont automotive lacquer thinner in butyrate dope is OK as long as it is the original type, ie: 3608S, 3602S, etc.  Never try to use the newer low VOC type lacquer thinner labeled V3608S, etc.  This stuff will not mix with dope and is not usable even to clean brushes or spray guns.

Whatever you do put as little dope in the fillet areas as possible.

Bill 

[Dan Berry]

DuPont 3608s thinner.

The plane has Ultracote on the wing.
The dope is on fuseleage/tail. It's lift at the wing/fuse. empennage and even the 1/8 ply doublers on the nose where they blend to the fuselage.

I don't have non-taughtening color available.
It's not my first goat. I never encountered this problem in my youth using AeroGloss. My Brodak clear didn't do this. If the Brodak color were fuel proof I might not be in this pickle.

[Dan McEntee]

  Lightly sand the areas again to get them clean, level and scuffed up. Mix up some more dope, and this time try the old method of adding a few drops of castor oil to the dope to plasticize it. I use epoxy and micro-balloons to make my fillets and have never had it lift from them, but I also always use Dave Brown's Flex-All in the dope mix for final colors. I don't know how available this is anymore, but I really think all it is really is medicinal castor oil. it looks the same , and I have given it a "taste test" with just a drop on my tongue when my curiosity got the best of me. 
  Good Luck and have fun,
   Dan McEntee

[Tim Wescott]

The fillet is just epoxy and microballoons.
It also does it on a simple 90` joint.

I'm not sure what you mean by "simple 90 degree joint", but if you mean a sharp inside bend, that's going to be worse than a fillet.

Sig white is low shrinkage.  Sig clear comes in both low and high shrink -- if your clear is Lite coat then it's low shrinkage.

That's low shrinkage, not no shrinkage.  All dopes shrink.  For that matter, all paints that harden by evaporation shrink (which pretty much means all one-part paints).  So unless you're willing to paint with catalyzed paint, you're stuck working around shrinkage.

Some pharmacies carry medicinal castor oil -- look.  The bottles that I found were 8-ounce, which is plenty for painting with dope.

[Hoss Cain]

DuPont 3608s thinner.
/// SNIP ///
I don't have non-taughtening color available.
It's not my first goat. I never encountered this problem in my youth using AeroGloss. My Brodak clear didn't do this. If the Brodak color were fuel proof I might not be in this pickle.

I have been using Brodak since it's inception. It is a well refined Randolph product. I have never had a problem with its fuel proof qualities. If you use the high-priced spread, AG, as I did in my old times, nothing else worked with it and if one did not let it cure for some time, it would blush big time  especially if one spilled some raw fuel on it. I don't know about SIG now, but in its early days it was simply repackaged Randolph. I owned a hobby shop in Mt. Prospect IL for some 7-8 years, "70s" and I carried all types of finish products, the hobby stuff and even real dope packaged for 1:1 scale.
Fillets made with anything other than talcum powder, (no additives) fine sanded balsa dust, and dope have IMO always caused trouble when painted over with dope.  In my experience way back when everything was dope and paper or silk, fillets could be a real pain, especially when I bought a kit early in the week to fly on Saturday. Of course back then I couldn't even spell "appperance points",    so nothing else mattered much.

[billbyles]

DuPont 3608s thinner.

The plane has Ultracote on the wing.
The dope is on fuseleage/tail. It's lift at the wing/fuse. empennage and even the 1/8 ply doublers on the nose where they blend to the fuselage.

I don't have non-taughtening color available.
It's not my first goat. I never encountered this problem in my youth using AeroGloss. My Brodak clear didn't do this. If the Brodak color were fuel proof I might not be in this pickle.

Dan,

"It's not my first goat. I never encountered this problem in my youth using AeroGloss."  Well, Dan, things change over the years; Aerogloss is not the same formulation today as it was in your youth, so sometimes you have adjust your techniques to suit the materials available these days.

Re-read my post above - I said that all Sig and Randolph colors are non-tautening, so if Sig or Randolph are the colored dope you are using then they are non-tautening.  The symptoms you describe - shrinking in the fillet areas - is because you are getting too much dope in the fillet area.  Even the dopes labeled "non-tautening" do shrink some.  Tautening type dopes shrink 10% to 12%.  Non-tautening dopes have plasticizer added, however they still shrink about 5%.  Adding additional plasticizer will help reduce the shrinkage, and should be used after the initial tautening type dope is applied over the open bays.

Since you said you are using Ultra-Cote on the wings then just use non-tautening dopes from the start.  While I don't use Brodak dopes I have heard many top builders state that they no longer use it due to its lack of being fuel-resistant.

I also use leather fillets on my models, and dope sticks extremely well to the leather - you will never have a problem with dope lifting with a leather fillet.  Paul Walker makes his fillets out of balsa, carving them & he has no problem with dope sticking to them.

[Dennis Toth]

Dan,
You mentioned that the fillets were epoxy and micro balloons, one thing about regular epoxy is you have to clean off the surface with degreaser after it cures to get it to take paint reliably. Epoxy have a wax in them to control the cure, the wax migrates to the surface as it cures (this is a very small amount). Simply take some degreaser or thinner on a paper towel and wipe it down a few times, then once that dries sand the surface with 400, wipe again (for good measure) and put a thin coat of non-tauting clear, go slow let it dry over night, then go into paint, again thin light coats and let them dry. If you get a lift spot, Windy use to say you can slit it with a razor blade and put in some thin CA and press it back down, then sand it off and fill in any dent with filler and continue painting.

Best,   DennisT

[Serge_Krauss]

Guys, it's not that hard a problem to avoid and doesn't need special materials. I've never had any lifting problems over my epoxy/microballoon fillets, with high-shrinkage Brodak butyrate dope. The prevention:

1) As Dennis says, sand the fillet with #400 paper, wrapped around an appropriately sized dowel, after the epoxy sets. If you want a really good fillet, you have to do this anyway.

2) Use a brush, but do not paint the whole width of the fillet at once. On my first clear coat, I brush a 50/50 coat overlapping only about about 1/3 of the fillet's width on each edge. Let that dry for a while (longer is better). Then brush a narrow strip down the center of the fillet to complete coverage. Let it gas off. Do this  one or two more times. Rough it up with wet (or dry) sanding (typically #400 again). I use Dupont Prep-Sol in my wet sanding, which may also help in removing residue. I've then sprayed thin color coats over the whole fillet area with no (that's NO) problem. This is with a very high-shrinkage butyrate (not even nitrate) dope.

I've posted this picture before, but note that there is no lifting on this decade-old, 30-minute epoxy and micro-balloon fillet. I've used this technique several times with no problems.

SK

[Hoss Cain]

  (SNIP)
...color coats over the whole fillet area with no (that's NO) problem. This is with a very high-shrinkage butyrate (not even nitrate) dope.

I've posted this picture before, but note that there is no lifting on this decade-old, 30-minute epoxy and micro-balloon fillet. I've used this technique several times with no problems.

SK

"Don't 'cha knows thet thar be a law  a'gin thet kind uf smooth and purty work?"

Well if thar ain't, thar oughta be."