alternatives to dope for silkspan?

I've been working on my first dope and silkspan covered plane since I was 16... I've had a "few" problems

1) the dope blushed (duh... this is Houston in the summer)
2) evicted from the house due to smell (see #1 above)
3) it turns out to be a migrane "trigger" (the final straw)

There have been a number of threads on alternatives to dope for filling, priming and final finishes. Two part paints, PC, etc.

But what about attaching and shrinking the silkspan on open framework construction? PC works well on solid sheet but doesn't shrink the silkspan. I'm not a big fan of the iron on plastics: I'm not able to get a good job that stays looking good. It sags and wrinkels in the sun, my application to compound curves leaves a lot to be desired...
I really need to find some alternative materials or process. Any leads?

>>But what about attaching and shrinking the silkspan on open
>framework construction?

Many Free Flight modelers attach their tissue with thinned white glue. This is more demanding when using Japanese tissue, since it has poor wet strength, but many successfully do this nonetheless. Since Silkspan has good wet strength, it should get along fine with a water-based adhesive. Try applying damp Silkspan with thinned white glue for an adhesive. Glue sticks can also be used. This does not solve your final finish problem, just the attachment. You might get a serviceable result using colored (or dyed) Silkspan and Minwax spray urethane varnish from a rattle can (Home Depot). Not too smelly, and dries quickly. Use the regular, since it yellows less than the spar varnish, which is *very* yellow. Be careful about weight, the urethane is much heavier than dope. Reasonably, but not absolutely fuel proof. Also Rustoleum in rattle cans, but again, *heavy*. Heat the cans in a bucket of hot water first to thin the paint. Try colored Silkspan on the wings and Rustoleum on the fuselage, with clear urethane on the Silkspan for fuel proofing.

>>>But what about attaching and shrinking the silkspan on open
>>framework construction?
>
>Many Free Flight modelers attach their tissue with thinned
>white glue. This is more demanding when using Japanese
>tissue, since it has poor wet strength, but many
>successfully do this nonetheless. Since Silkspan has good
>wet strength, it should get along fine with a water-based
>adhesive. Try applying damp Silkspan with thinned white
>glue for an adhesive. Glue sticks can also be used. This
>does not solve your final finish problem, just the
>attachment. You might get a serviceable result using
>colored (or dyed) Silkspan and Minwax spray urethane varnish
>from a rattle can (Home Depot). Not too smelly, and dries
>quickly. Use the regular, since it yellows less than the
>spar varnish, which is *very* yellow. Be careful about
>weight, the urethane is much heavier than dope. Reasonably,
>but not absolutely fuel proof. Also Rustoleum in rattle
>cans, but again, *heavy*. Heat the cans in a bucket of hot
>water first to thin the paint. Try colored Silkspan on the
>wings and Rustoleum on the fuselage, with clear urethane on
>the Silkspan for fuel proofing.
>
>Andy

Yeah. I used to do this too. But we always shrank the paper with dope after attaching it... It does shirnk some when drying but not as much as after doping. I guess the only real alternative is the heat shrink polyester stuff... "Fibafilm" is one example. There are many others. some of them are pretty heavy: Super Coverite for example. What are the favorites? and how well do they go around compound curves like wing tips etc.? Most of the ones I've ever tried get really heavy if you try to fill them.

Ron,

My current plane is "dopeless". I used polycrylic from the wood up. On the open bays, I wetted the silkspan and used PC around the edges and let it tighten up, then put thinned PC on the paper over the bays and used a hair dryer to tighten it up again. Had to do this a couple of times, but in the end it came out pretty well. Takes a lot of patience, but it works.

One caution. I wouldn't put the PC on bare wood again. If I do a finish this way again, I'll hit the bare wood with at least one coat of nitrate. Straight, water based Polycrylic is not a good thing on 4 pound balsa, especially if it's only marginally supported. Took a long time to get out the warps in the wood.

Ditto on the warping issue with PC over sheeting. I'll never do that again. I think the best approach (based on my limited experiments) is to put the silkspan on in the traditional way with nitrate dope (outside, where the stink won't be a problem), but only use two light coats of nitrate over the silkspan and over any bare wood, just enough to provide a water barrier. Then go at it (indoors!) with the PC. You will still need to use a hair dryer to tighten it up as you go, but that's no big deal if you started with the nitrate.

Use the West Systems filler (410) if you want to bulk up the PC for a filler coat. After the PC you can do what you want (if dope, then be sure to use a sanded coat of primer so the dope sticks).

I know nothing about auto paint but it seems a good way to go, and Randy's planes are beautiful. (I'm still waiting for the "no stink" color coat solution... any ideas?)

The blushing will come out after new wet coats thinned, are applied. Lots of moving air will prevent those headaches. I really get them when I use Nitrate vs Butyrate dopes. Do you have a garage? The humidity here in Huntsville, AL is in the 85% plus range almost all summer, so I know what you are going through.
After three heavy coats of clear on the wing, apply the very damp silkspan using only thinner. Rub it in with your fingers. Pull it as tight as you can, in both span and chord directions. Spray it to keep it damp as you do this. Then after it has dried overnight, it should be fairly taught. Then try the Minwax blue can polycrylic. I have never used it over the silkspan, just the balsa, so it may not work. Maybe one coat of thinned clear, dried over night, then the PC might work.
I have found that working with polyspan to be a cross between silk and silkspan, but I use only silkspan on the tips and compound corners. It does take a little more finesse, especially with a heat gun as this stuff will run if too hot. But it fills quicker, it much stronger, just get the shiney side up. DON'T sand this stuff until you have at least three coats of dope over it. It will fuzz up and give you fits. But once you have learned how to use it, you will very seldom use silk or silkspan again.

LAST EDITED ON Jul-20-04 AT 05:47 PM (CDT)
 
I too have been searching for a satisfactory substitute for dope...because of $$$ and fumes. I've covered one airplane so far with silkspan and Elmer's thinned half-&-half. It worked OK but I think it was too thin; next time I'll cut it maybe two to one, glue to water. I then put about 3 coats of the same stuff over everything to shrink it; finished with Rustoleum. Have flown it several times; seems OK but the covering could be a little tighter. A heat gun tightens it up for awhile, but it seems to stretch or something after a few flights, not really saggy but sort of "soft" feeling. The Rustoleum seems totally fuelproof, whether raw or from exhaust. Weight about matches plastic covering. I'm continuing to experiment; open to any suggestions.
--Ray

As an aside - silkspan and Elmer's works very well over bare foam. After the silkspan dries, you have a nice, stiff wing which you can then cover with Solarfilm or some other low temp film. This was Ron St. Jean's method (he used, IIRC, Saran Wrap as the final layer).

>I too have been searching for a satisfactory substitute for
>dope...because of $$$ and fumes. I've covered one airplane
>so far with silkspan and Elmer's thinned half-&-half. It
>worked OK but I think it was too thin; next time I'll cut it
>maybe two to one, glue to water. I then put about 3 coats of
>the same stuff over everything to shrink it; finished with
>Rustoleum. Have flown it several times; seems OK but the
>covering could be a little tighter. A heat gun tightens it
>up for awhile, but it seems to stretch or something after a
>few flights, not really saggy but sort of "soft" feeling.
>The Rustoleum seems totally fuelproof, whether raw or from
>exhaust. Weight about matches plastic covering. I'm
>continuing to experiment; open to any suggestions.
>--Ray

Ah! That reminds me: white glue is also a pretty good heat activated adhesive too. Paint it on and let it dry. It is then possible to iron covering over it and have it stick. Sort of like water based Balsarite or Stixit. Might we worth a little experimentation...

Hmmm,

I have a really good idea. Use Polyspan stuck down with the thinned white glue. Then after you shrink the Polyspan with a heat gun you can paint it with anything you like. Just make sure the last coat or two is relatively fuel proof.

>Hmmm,
>
>I have a really good idea. Use Polyspan stuck down with the
>thinned white glue. Then after you shrink the Polyspan with
>a heat gun you can paint it with anything you like. Just
>make sure the last coat or two is relatively fuel proof.
>
>Jim Pollock

That's an interesting thought. I've attached a link to an article about applying Polyspan. This one still uses some nitrate. The thinned white glue might work well. We used to use thinned white glue to attach skins to foam core wings, then iron it to "set" the glue. Some caution was necessary because you could easily over heat the core and deform it. Just about everybody that I know has swithched to using laminating epoxy for skinning now but the idea here is that perhaps you could roll the polyspan around corners with a monocoat iron.

http://www.faimodelsupply.com/starline-polyspan3.htm

Or...you could talk a friend into letting you paint at his house and let him address the fumes problem.

> Or...you could talk a friend into letting you paint at his
>house and let him address the fumes problem.
>
>George

NIMBY?

I did some more reading in the archives. Looks like alternative coverings have been a popular topic! There's more than one way to skin a cat. In summary: the non-woven ones are more difficult to get around compound curves and the woven ones are heavier when finished. Almost all the posters used some dope in the process: usually Nitrate. It seems that nitrate dope is lighter and dries faster than PC. Some posters mixed woven and non-woven materials using each where it worked best e.g. woven stuff on compound curves like wing tips.