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Jun 14, 2019, 10:42 AM
I Hate Orange Props
MicroPlane6's Avatar
Thread OP
Help!

Koverall application streaky


I’ve covered the wing of a 3.5m glider with Sig Koverall + clear butyrate dope (Sig Supercoat). The end result was somewhat “streaky.” It had streaks where the cloth was more opaque or shiny. Due to unrelated stuff, I decided to strip the covering off and try again. This time it is still streaky. My covering process was: dope the frame twice, sanding between; apply cloth by brushing lacquer thinner on, so that it soaks through into the dope; then applying 50/50 lacquer thinner/dope.
Am I doing this wrong? I don’t want to use colored dope or paint on the wings; I want them to remain uncolored.
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Jun 14, 2019, 11:10 AM
JOE MOCERI
I have used the Koverall just recently and I had the same streaks after covering. It really didnt bother me since I was Painting. I think The streak showed up after shrinking the material. I as I think back it may have been the sheen of the weave where pulled tighter or where there was a crease from being folded in the bag.
Jun 14, 2019, 12:19 PM
I Hate Orange Props
MicroPlane6's Avatar
Thread OP
It shows up somewhat before heating/shrinking. Here are some pictures.
Maybe using water-based polyutherane instead of dope will work better?
Jun 14, 2019, 12:32 PM
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gene6029's Avatar
I use Sig Koverall a lot. What you are seeing I believe is the clear dope you are applying is heavier in some areas. ( the areas that are lighter is where the clear dope is thinner). Have you tried going over just the lighter areas with a 60 - 70% thinner and clear to see if it changes to match the rest of your covering shade? I have not used Koverall to have a translucent finish myself, but have seen this on my models before putting down any primer or color. I am guessing this is after you put down the clear, correct? I definitely have seen this though myself.....Gene
Jun 14, 2019, 12:43 PM
Registered User
gene6029's Avatar
Just another thought. Do you think your clear is blushing? If so, try applying straight thinner over the areas and see if that clears it up. ( just a thought)...Gene
Jun 14, 2019, 01:35 PM
I Hate Orange Props
MicroPlane6's Avatar
Thread OP
What is “blushing?”
This is the first time I’ve tried working with dope and Koverall.
Jun 14, 2019, 04:47 PM
Registered User
gene6029's Avatar
Ok, blushing is painting on dope when the humidity is high. The dope traps moisture in and gives off a foggy or dull look. Usually applying pure thinner over the area when the humidity is lower releases the moisture and the dope dries clear and shiny. I have gotten away painting in higher humidity by using retarder in the dope. Im not really sure that's your issue though, its hard to tell with the pictures. I looked back at some of the pictures I took of my cover jobs using Koverall, and it looks like I had some streaks, but since I painted over it I never gave it a thought....gene
Last edited by gene6029; Jun 14, 2019 at 05:01 PM.
Jun 14, 2019, 06:54 PM
Registered User
Quote:
Originally Posted by MicroPlane6
It shows up somewhat before heating/shrinking. Here are some pictures.
Maybe using water-based polyutherane instead of dope will work better?

I don't have a diagnosis/solution..... but could you clarify some things:


"It shows up somewhat before heating/shrinking".
I shrink or snuggly tighten the Koverall in the open areas with an covering iron BEFORE applying any dope.

You use the term "lacquer thinner"...…. is the thinner totally compatible with the Sig butyrate clear dope? (is it Sig/Randolph or other recommended thinner?) ….. just about any big store lacquer thinner is ok for cleaning dope brushes but may not thin dope in a satisfactory manner.

Sometimes initial thinned dope coats erratically leak thru the fabric and collect on the underside.... but usually in the junctures with the balsa structure..... how many coats of thinned dope have you applied?

Water based polyurethane?...…. people are experimenting with lots of off the shelf products since dope has become pricey/more difficult to get..... do a search with google using words such as "water based poly on Koverall", perhaps adding at times forum names, especially "stunthanger" as the people who hang out there have done a lot of experimenting.
Since your application does involve the need for any fuel proofing, on that account water based coatings would be fine.... the issue I see is the water content possibly "relaxing"/loosening the heat tightened fabric..... one possible work around this issue is to first apply several "smudge" coats with a brush just damp with poly, rubbing the poly into the fabric so that over several such coats the surface is sealed - the fabric will feel smooth/hard - after which "wet" coats can be applied. Always good to experiment on scrap structure first.


Michael in Ontario, Canada
Jun 14, 2019, 07:14 PM
Registered User
gene6029's Avatar
I dont want to get off track here, but I have never attached Sig Koverall with dope. I use dope to attach silk or silkspan. Not saying it shouldn't be done, I just use Stix-it directly on the wood, then apply the Koverall just like Monokote with a heat iron. The Chipmunk in my avitar was done that way, then I used a foam brush to seal the Koverall with Minwax Polycrylic. Then primed with rattlecan DC-540 then latex house paint. The Koverall was not translucent after applying the poly. If that's the look your after I would use silk or silkspan personally. None of this really helps you now but I would choose silk or silkspan for lighter weight than Koverall on a glider wing.....Gene
Jun 15, 2019, 04:40 AM
Registered User
Quote:
Originally Posted by MicroPlane6
I’ve covered the wing of a 3.5m glider with Sig Koverall + clear butyrate dope (Sig Supercoat). The end result was somewhat “streaky.” It had streaks where the cloth was more opaque or shiny. Due to unrelated stuff, I decided to strip the covering off and try again. This time it is still streaky. My covering process was: dope the frame twice, sanding between; apply cloth by brushing lacquer thinner on, so that it soaks through into the dope; then applying 50/50 lacquer thinner/dope.
Am I doing this wrong? I don’t want to use colored dope or paint on the wings; I want them to remain uncolored.

Looks good to me. You just don't have enough dope on yet. Brush on a couple of coats of 100% dope to get it into the weave of the fabric. Then switch to spraying and spray on 3 or 4 more coats. You should get a good overall sheen. You'll have to lightly sand inbetween coats for it to look it's best.

I adhere the fabric to the wood using 100% dope instead of lacquer thinner. It takes a lot of dope to get a good enough build up for it to look good. Add some retarder to your dope to prevent blushing and to get a better overall sheen.

Carl


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