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Building Tips and technical articles. => Paint and finishing => Topic started by: Marty Hammersmith on November 28, 2019, 12:55:37 PM
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Well, so far so good. For people who have wondered but didn't want to take one for the team, I'm plans building a hand launch R/C plane called a Crazy Thing by Precision Aero. If you go on their website, the picture they use for the Crazy Thing is also one of my airplanes built more than 15 years ago. The Monokote still looks good but is becoming a little fragile and there are always a few small wrinkles that pop up now and then. I wanted to play with Koverall again. I did two airplanes many years ago using Poly Fiber materials. This time I'm trying dope for the first time ever. so, this Crazy Thing is fiberglass and thinned West System epoxy on the solid surfaces and Sig Koverall on the open panel wings.
About compatibility. The Sig Koverall was applied using Sig Stix-It straight out of the can. The base coats are Sig clear nitrate dope. I'm thinning it with MEK without issue. Over that went Brodak Sanding sealer which is butyrate dope and talc. I thinned that with MEK as well. I'm into the color coat now. I wanted a translucent color on the solid fiberglassed balsa surfaces to partially mask the wood but still let it show through a little. To do that I mixed about 3 parts sanding sealer with 1 part Brodak colored dope. I thinned it all with MEK then added retarder to slow down the drying time. MEK dries fast and spraying speeds that up even more hence the retarder which I found necessary even when brushing. The wings will be a solid version of the color thinned with MEK and Brodak retarder to prevent blushing.
I am confident in the compatibility of MEK with these materials. It's even listed as an ingredient so how can it not be compatible?
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Mr. Marty,
What is Koverall, and how is it different from silkspan or tissue?
Can StixIt be used for tissue? I was given a can, but am used to sticking the covering with nitrate/butyrate.
I'll be watching this thread develop before I decide to toss this can of magic stuff.
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Hi Marty;
The only product lines that was different was the Brodak sanding sealer, and people have used that with SIG products before. They may even come from the same origin manufacturer. Using MEK to thin all the way through is helpful in making things compatible. Using SIG nitrate goes as the base coat for the Koverall goes right with their recommendations, I believe. There is another thread here that mentions using nitrate as a base coat on polyester coverings is recommended for better bonding of the base coats to the material. I would say that you were right on the money with things.
Jim;
Koverall is s SIG product that is a heavier cloth covering that is like a polyester dress lining. Heavier than polyspan and very durable. Applies with Stix-It or dope and heat shrink with an iron. Too heavy for small models and free flight stuff. Stix-It is a heat activated adhesive that you would use for any iron on material. I like it better that Balsarite. I haven't tried it with polyspan yet but should work I would think but might need to be thinned a bit. If you have a used model that you are recovering and had to treat some oil soaked balsa, a coat of Stix-It will help you make sure the new covering sticks down like it is supposed to.
Type at you later,
Dan McEntee
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Thanks for the comments Dan. In regards to mixing only Sig and Brodak brands, that's right. In addition I've seen discussion about people afraid to use nitrate thinner with butyrate and vice versa. I'm just trying to keep the shelf as simple as I can. Stix It to hold the Koverall in place. Nitrate to fill, butyrate to color, and MEK to thin everything.
How many people use silver after the nitrate as a sanding base to see all of the flaws. Given the nature of this model, I drew the line short of doing that. I went straight to color though I'm wishing I'd shot a base of white first. Might have reduced the number of coats needed for opacity on the wings. I was looking for and achieved translucent on the fuselage but I'm looking for opacity on the wings. It's coming.
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Just for a bit more safety I’d use lacquer thinner and not MEK. That is extremely toxic. Back when I was a speed boat designer we had a young lady on our production line where MEK was used lose a baby. It was thought the MEK was responsible. None of it is good but that is a little worse. We had to handle it with more caution than acetone which was used in huge quantities.
Dave
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Follow manufacturer's recommendations. If not, good luck. It's a crap shoot.
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Follow manufacturer's recommendations. If not, good luck. It's a crap shoot.
It's a model airplane, I'll take my chances mixing the product lines.
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We used Mek to clean our hands back in the day. That's crazy. I use cheap hardwhere store lacquer thinner to thin my dope. It's also cheaper than the Mek or acetone. Works for me. Plus I don't need to buy any retarder for it. 😁
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Thanks for the comments Kevin. That seems a natural move and as you say, will probably reduce or eliminate the need for retarded. I started with MEK because of comments I read about problems the writer attributed to using cheap lacquer thinner.
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We used Mek to clean our hands back in the day. That's crazy. I use cheap hardwhere store lacquer thinner to thin my dope. It's also cheaper than the Mek or acetone. Works for me. Plus I don't need to buy any retarder for it. 😁
Kevin, just FYI lacquer thinner contains MEK, acetone, ethyl acetate, and several other solvents.
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You guys can sit down now, I use ethanol to thin dope too.
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I found out Saturday that Costco uses ethanol to thin their eggnog.