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Building Tips and technical articles. => Paint and finishing => Topic started by: Mark Mc on September 28, 2017, 01:42:37 AM
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I didn’t want to clutter up the Dr. Office Tissue Paper thread in the Open section, or Larry’s SLC Over Polyspan thread here with my foolishness, so I’ll start another thread. I have a Goldberg Shoestring project that’s a couple of years overdue to be worked on. It was given to me by the husband of one of my wife’s friends. They were moving out of their house so it could be re-built, and the wife wanted him to get rid of his old modelling stuff he hadn’t played with in 30 years. He gave me several engines and left over building supplies, and one crashed Shoestring. I took it home and stripped the silkspan covering. The fuselage nose was fuel soaked, and the crash wiped out the rear of the fuse, but the wing is in pretty good shape. I’ll do a pull test to make sure the bellcrank isn’t coming out, and then cut a new fuselage for it. I’m a Monokote guy, but I figured I’d do a Silkspan covering on it, get the McCoy .35 Redhead running nice and steady, and then give it back to him. He can still fly, as he had no problem flying my FliteStreak. His wife will be none too happy to see it return, but I think he really deserves to have the plane back.
But, I’m pretty cheap. That happens when you’re getting close to retirement. So when one of the members here offered to sell one of the rolls of Exam Paper for $2.50 plus shipping, I jumped on it, figuring I’d use that and learn as I go. Then reading on the Dr. Office Tissue Question thread about Larry’s method of SLC over Polyspan, I started thinking about a roll of Doculam I got a couple of years ago. I don’t remember if it’s 1.5 or 2mil lamination film, but I got it so I want to use it. I wish I had a bare wing I can try doing a Doculam over Dr.’s exam paper test, but nothing’s uncovered at the moment. I’ll have to make a box with four or five ribs and try it.
Do Y’all see any unsolvable problem with using Doculam over doctor’s exam table crepe paper? Since I’m snarky, I decided to refer to this as the DocuDoc ™ Covering Method.
For the glue, I have nitrate dope, but I’m working in the room next to our bedroom and don’t want to use that. I don’t have any Modge Podge, but I could run out to the crafts store and pick up a bottle if I have to. What I DO have is a bottle of Eze Dope. I used it on .010 and .049 planes earlier this year and it was acceptable. Do Y’all think that would do an adequate job of gluing down the crepe paper?
How would Y’all paint the Doculam when it’s all covered? The plane was previously painted green, but I want to do it in the 8 parts Cub Yellow to 1 part Cessna Green specified for the Shoestring.
Mark
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Be brave. Use what you have. It will most likely be just fine.
Worst case is that you have to tear it off and try something else.
I have tried D&K Lamination film over fabric lining (poor mans polyspan) and the adhesion was great. Very strong composite covering.
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I truly think the Mod-Podge is a thicker version of Elmers White Glue. I have used Elmers white glue to adhere 1/16 balsa to ribs with a super hot iron. I have also used the Elmers on wing tips putting the covering down. The DocuLam is a heat activated mylar. I believe the extra strength comes from the combination of the two materials. But you never know until you try some thing if it will work or not. Let us know how yours works. D>K
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Any update, Mark Mc?
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About the only problem with Doculam and similar films is that they are 2-3 times as thick as is needed. Putting the polyester film over silkspan or tissue, or polyspan makes it the base coat of the finish, replacing dope or something else. It prevents the porous base covering from absorbing lots of dope. A thicker film is like using 20 coats of dope before starting the color.
If you want a light, strong, old tyme style finish, put thin tissure or silkspan over really thin polyester film. The film makes the covering pretty damage resistant and greatly reduces the amount of dope needed to fill the silkspan.
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What are the pro's and cons of each method-
1. SLC first with tissue, silkspan, or polyspan over it.
2. Tissue, silkspan, or polyspan with SLC over it.
The way i see it, with the SLC on first, the adhesion is all but guaranteed to the airframe. The outer layer could then be problematic to stick to that. Should need roughing up prior to any paint, but should be lightest.
With the silkspan, tissue or polyspan under SLC, you'll have to keep trim to a minimum over the base layer, or you could run into problems with bubbling or bonding. No need for clear over the top, unless the trim tissue is applied over the SLC, right?
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I have done it both ways and now consider the mylar is to go on top of base covering(silk span, doctor paper and poly ester cloth). When I get ready to add color I buff the mylar with a sponge scouring pad before spraying color. So far no grin showing through. I still haven't done the nose as weather turned too cold and windy. H^^
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What are the pro's and cons of each method-
I haven't tried either, but I know the free flight guys use silkspan or tissue over really freaking thin Mylar. Their strengths compliment each other (Mylar is more puncture resistant than tissue or silkspan), and the Mylar seals the paper so that you need far fewer coats of dope. Then you finish the plane out the same as for tissue/silkspan.
Were I going to try one or the other, I'd go on the "this works for lots of other people" principle, and do paper over Mylar. Or, I might pay attention to Doc, at least to the extent of doing the wing one way and the tail the other, and see which seems to be better in the long run.
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Like any thing it takes practice and patience(what ever that is). The silk span over mylar will give the natural dope finish with less dope. Make sure mylar is buffed to a dull surface finish. D>K