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General control line discussion => Open Forum => Topic started by: kevin king on November 07, 2018, 09:03:58 AM

Title: Polyurethane vs Dope
Post by: kevin king on November 07, 2018, 09:03:58 AM
Here's why I'm reluctant to use Polyurethane paint on an open bay balsa wing covered with silkspan: To brittle. https://youtu.be/ov_Yl_3CQmE

The blue paint is dope. The white is polyurethane
Title: Re: Polyurethane vs Dope
Post by: Ara Dedekian on November 07, 2018, 10:11:39 AM


        Here's what happened to the Urethane on my Flying Clown wing just sitting in the attic in extremes of heat and cold. The covering, scuffed up with OOO steel wool,was Doculam, a heavier grade of Phil C's SLC covering. It did adhere to the silkspan over balsa but I may have clear coated the fuselage with the old K&B clear epoxy.


        The urethane was water based System Three Inc. marine paint over their two part primer. Nelson Products, who used to advertise in Model Aviation, distributed the products to modelers.
 
        Ara
Title: Re: Polyurethane vs Dope
Post by: Brett Buck on November 07, 2018, 10:14:56 AM

        Here's what happened to the Urethane on my Flying Clown wing just sitting in the attic in extremes of heat and cold. The covering, scuffed up with OOO steel wool,was Doculam, a heavier grade of Phil C's SLC covering. It did adhere to the silkspan over balsa but I may have clear coated the fuselage with the old K&B clear epoxy.

    It is not at all surprising that nothing sticks to a slick laminating plastic!  That's why it is not used for stunt planes, generally.


     Brett
Title: Re: Polyurethane vs Dope
Post by: Ara Dedekian on November 07, 2018, 10:44:18 AM
    It is not at all surprising that nothing sticks to a slick laminating plastic!  That's why it is not used for stunt planes, generally.


     Brett

     Lesson learned, the hard way!

     Ara
Title: Re: Polyurethane vs Dope
Post by: Brett Buck on November 07, 2018, 11:18:05 AM
     Lesson learned, the hard way!

  Sometimes, you just have to find out for yourself! We have had something experimental go wrong.

    BTW, to the topic, dope would have flaked off almost as soon as it dried, polyurethane had a better chance.

    Brett
Title: Re: Polyurethane vs Dope
Post by: john e. holliday on November 07, 2018, 11:45:22 AM
I have found using the SLC type covering, it needs a really good buffing and clean surface.  Then spray a good primer before dope or or the Rustoleum paints.    D>K
Title: Re: Polyurethane vs Dope
Post by: kenneth cook on November 07, 2018, 02:16:12 PM
             Having talked with Jerry Nelson on numerous occasions and I still use the Systems 3 WBPU it was not intended to go on synthetic films. I'm surprised it lasted that long. It does the same thing in no time at all if used over butyrate dope which is what caused me to have numerous discussions with Jerry. From that point on, I used nitrate as a base and it never failed and has held up better than any dope I ever used. I have numerous planes painted with it. It can be applied over synthetic coverings such as Koverall or nylon when cross linker is applied to keep it from migrating through the weave but film doesn't work.