Dope problems

Stuka Stunt Main Forum · 6 of 6 known posts recovered

Jim DeYoung · Apr 18, 2001 07:07 PM

I am in the process of painting 6 sheet balsa, .049 powered, airplanes. The planes were scratch built with a church group of 6th & 7th grade boys. The design is very similar to the Carl Goldberg STUNTMAN 23. Things were going fine until I tried to remove some masking tape-not just any masking tape-but scotch brand drafting tape,which has very low tack. The tape pulled off the dope down to bare balsa. About 50% of the area under the tape was left bare. It was not just an isolated spot but all over the plane. I think on the rest of the planes I will be forced to leave them one color.
Here is the painting sequence I used:
-2 coats Sig clear dope thinned 100% w/Dupont thinner
-3 coats Sig clear with some zink st.
filler, sprayed, sanded between coats.
-Epoxy fillets added and sanded
-1 coat Dupont Fill N Sand sprayed and 80%
90% sanded off- all sanding done with 320
grit paper.
-1 coat Sig white with 25% gray thinned
100% with Dupont thinner,sprayed.

At this point things were looking good . Most of the grain was filled in and they looked good! This is where I used some masking tape and ran into trouble. It seems there is almost no adheasion between bare balsa and butyrate dope. Any Advise?

gcb · Apr 18, 2001 07:22 PM

#1 source

Try heating the masking tape with a heat gun as you remove it. Careful to not blister the paint.
I have not tried this, but I read it on one of the forums.
Good luck,
George

LNeumann · Apr 18, 2001 08:05 PM

#2 source

We always use butyrate. We only use butyrate. It does stick to balsa. However, you can get meltdown with too much thinner or too slow of a drying thinner. You can also get problems if you wait too long between coats (without sanding) or paint too soon.

And the dope needs to "gas off". That thinner needs to evaporate out. SIG dope is notorious for drying slowly, and, if you used another thinner (which DuPont thinner? Was it 3608S?) that could add to the problem. The problem is, if it skims over on top and still needs to dry underneath, it will bubble itself off. And, if the thinner melts all the way in, it will take everything with it. This could be the basic problem of what happened to you.

Until the dope is absolutely dry (maybe a month for SIG) the tape can be a problem pulling up. When you remove the tape, try simply pulling the tape back on itself. That way it doesn't have so much upward pressure and you are far less likely to remove paint underneath when you remove the tape.

Leonard Neumann

Jake · Apr 18, 2001 08:07 PM

#3 source

LAST EDITED ON Apr-18-01 AT 08:12 PM (EST)

You said the magic words "Sig dope". That is the root cause of your problem. I no longer use it because of this. Do yourself and the children a VAST favor and ditch the Sig and go with Brodak or Aerogloss, you will all be a LOT happier in the end. I am sure Leonard can hook you up with a good mail order deal with Brodak.
By the way Leonard, I pulled the wheelpants off a model this evening for a little maintainence; it was doped with Sig, dried many MONTHS now. Guess what? The dope peeled off the pants in several spots and stuck to the brackets! Bye Bye forever Sig. This isn't the first time I have had a problem with Sig dope, but it is the LAST time for sure.

JAK

Larry F · Apr 18, 2001 09:23 PM

#4 source

Jim --

The reason you got valuable responses is that you provided essential detail on all aspects of what you did and what happened.

Reminder to all of us -- Follow Jim's question as a model of how to ask a question and we are almost guaranteed useful responses.

Larry F

dave siegler · Apr 19, 2001 09:19 AM

#5 source

Removing tapes can alway be problematic. When I worked on full scale aircraft I saw a over hyper owner ruin a many thousand dollar paint job (Imeron 3 color metal flake on a beech 18) because he ripped off the tapes while we were at lunch. It was a lot of work and he wanted it redone for free. We liked to remove the tapes while the paint was set but not fully cured. It seemed to work well. BTW we sprayed over a epoxy primer, and never had a paint adheision problem in any weather condition. The stuff was like glue. I felt sorry for the guy that had to strip and repaint one of our jobs. ( but we wern't all that smart we used simple dust masks to spray imeron not too healthy duh)

Always pull tapes back on itself, slowly and slightly away from the paint line. Work very slowly, don't hurry. Also make sure the base paint is fully cured before the taping process, or the paint may bond to the tape!

I have had many low tack tapes get very sticky when exposed to dope (brushed), I wonder if the glue is softened enough by the dope or thinner to caued problems?

I have not had adhesion problems with sig dopes, but other paints areogloss and rustolem when the tapes were not properly removed.

Dave