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Old Mar 16, 2013, 11:04 AM
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Canada, ON, Hamilton
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dope vs water base


David, your plan,...“ use esaki tissue over doculam and attach the tissue to the doculam either with permanent purple glue stick, such as UHU, or with thinned dope, shrink the tissue with alcohol which evaporates quickly, continue doping as usual.” sounds perfect.

For me, getting dope (quarts) is costly. While at the “paint store” I found clear brushing laquer, one litre size, for $15. I’ll post a picture of the can.

Regarding the “water base” clear finishes (used for wood working/finishing, etc.) They are probably just as good as dope for sticking tissue over Doculam. Maybe even better...they don’t smell!

I’ll have to try adding either a dye or food colouring to “water base” clear finishes to see what transparent colours can be made.

This will give two options:
colour/dye the tissue, or
colour/dye the “water base” clear finishes and apply to the tissue.

Earlier, above, a suggestion was made that Doculam can be died. This sounds very good.

Lastly, some of the water base paints are not fuel proof. Not a problem as they can be clear coated with butrate dope (a laquer/solvent based) and fuel proofed. The little Blue Flame shown in my blog has the balsa fuselage painted with water based coloured paint and then clear coated with dope. It’s lasted many years!

John
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Old Mar 16, 2013, 12:19 PM
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United States, SC, Charleston
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I have to order dope as well too, and it is expensive no matter where you are. I build mostly 1/2a to .15 sized models in the vintage categories and don't use enough dope to justify buying something like Randolph dope in the gallon cans, so I still periodically order pints or quarts of SIG Lite Coat dope, which is a somewhat non-taughtening, reasonably fuel resistant butyrate dope. I do not use nitrate at all. I tried water-based minwax polycrylic one time on a model maybe 10 years or so ago. It took so long to dry that I swore never again, but a lot of guys who have to work indoors and can't accommodate harsh chemicals have used it to attach fiberglass cloth in lieu of resin or dope. The polycrylic was not fuel proof at all and that particular model then required a coat of clear epoxy, so it ended up not being advantageous for me.

Of course, if you are flying electric, then a whole range of products open up for use, but I still fly mostly glow...

I really like using the permanent purple glue sticks as an adhesive for covering. (Purple because you can see where you are putting it - they dry clear.) Glue stick responds very well to a heat iron - I put the covering on the framework while the glue is still slightly tacky and pull it tight before the application of low to barely moderate heat. The heat from the iron melts the tacky glue right into the weave or grain of the covering material. Some brands of glue stick are water soluble, so I assume not fuel proof, but I seal over with many coats of thinned dope and, depending on the model size and weight, a final coat or two of spray can polyurethane for added fuel resistance. I am told the UHU brand purple glue stick is the best for model use and the one most in use by the free flight guys as a covering adhesive. Works with clear mylar, tissue polyspan, etc...

There has been a fair amount of discussion of this topic on some of the yahoo groups, including SAMTalk and I think a similar free flight group, although I cannot recall the name, from which I first learned about the use of these techniques.

So, I will keep experimenting and learning from what other folks like you are doing as well. I liked the idea of floral spray on the inside of the doculam. That would seem to make for a quick finish and I will have to try that too on something, maybe a glider.

This group has been very helpful on an astonishingly wide range of topics since I recently joined. It makes up for the loss of a gathering for such discussions by builders and craftsmen at the flying field or local hobby shop, which has all but gone away these days....
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Old Mar 16, 2013, 04:12 PM
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The water based polyurethane varnishes sold for such applications as wooden floor finishing work fine with tissue (Esaki) over mylar or doculam. Just apply the tissue wet and brush the varnish through. Shrinks and drys tight as with dope. No smell, no problem. The three examples below all use a French varnish called V3V.

The varnish itself does not shrink the tissue, as shrinking nitrate dope does, all the shrinkage is water shrinking, so the result does not pull or warp light structures as much yet still has good torsional stiffness.
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Old Mar 17, 2013, 03:32 AM
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Sundancer,
Nice models and finishes - signs of a mis-spent youth
john
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Old Mar 17, 2013, 09:29 AM
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Quote:
Originally Posted by pulserudder View Post
I have to order dope as well too, and it is expensive no matter where you are. I build mostly 1/2a to .15 sized models in the vintage categories and don't use enough dope to justify buying something like Randolph dope in the gallon cans, so I still periodically order pints or quarts of SIG Lite Coat dope, which is a somewhat non-taughtening, reasonably fuel resistant butyrate dope. ....
PR --

Aircraft Spruce offers Randolph coatings in quarts --- I buy all my clears and thinners from them. You've got the choice of nitrate or butyrate in both tautening and non-tautening mixes. In quart containers, there are no hazmat fees, so shipping is not too expensive.

For cleanup, I use lacquer thinner from one of the local hardware chains. I have also used it for some thinning of dope for brushing clears, but did find that it did cause some clumping of pigment with some of the colors. The colored dope that I thinned was old, so I don't know if it were due to the lacquer thinner or tied to the age of the dope.

http://www.aircraftspruce.com/menus/...hcoatings.html

andrew
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Old Mar 19, 2013, 09:14 AM
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primer, coatings, laquer for Doculam

Here are common model products and something else I recently came across.
Some are half the price of dope.

But remember, you will not beat the results of a good

dope and silk finish.

Having said that, these products may work with mylar and Doculam.

The gray - water based- primer sticks to balsa, fairly well to Doculam, and can be painted over with SIG dope.

I have tried ironing Doculam down and over the gray primer- it sticks to it and does not destroy the primer.

John
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Old Mar 19, 2013, 09:44 AM
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gray primer test

I coated mylar and Doculam with gray primer.
Let the primer dry.
Then crumpled it up to see if it stuck or flaked off.
It stuck better than dope.
John
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Old Mar 19, 2013, 08:16 PM
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John -

Did you do any surface prep for the shiny side (outside)? I've wiped it down with acetone, buffed it with one of those green Scotch Brite pads to dull it, then wiped it down again. That seems to give the doculam enough teeth to stick well.

My local Lowe's used to carry Varathane, but it was OOS last weekend. I was wondering since it's water based if the clear gloss could be colored with aniline dye, RIT dye or one of the dyes used for silk or wool. I'm always looking for a suitable, but less expensive, substitute for dope, especially colored dope.

BTW, thanks for the hands on testing --- nothing works as well as putting rubber to the road and checking for wear.

andrew
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Old Mar 19, 2013, 08:33 PM
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Is varathane fuel resistant?
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Old Mar 20, 2013, 01:17 PM
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Andrew, no , I did not do anything to the surface yet. No washing, no scuffing. The gray primer seems to have stuck better to the adhesive side (rather than the shinny outside) of the Doculam. Perhaps a wipe with acetone, or MEK(use out side in fresh air) would help. The clear Varathane seems to stick very well. I would guess/hope, that a dye or food colouring added to the clear might make a nice transparent coating. Maybe even mixing a little coloured water base paint would work out.

I have yet to try the fiber glass coloured pigments (solid, non transparent colours); they are solvent based, but will dissolve in MEK/acetone which may then carry them into a water base (using acetone, ethanol).

Note: water based paints can be "thinned' and equipment cleaned up using wind shield washer fluid.


PR- The water based coatings are not fuel resistant, however I have been able to top coat them with dope (Sig, clear). I found what worked best for me was a warm day, outside, spray on a few very light coats of dope, allow to dry, then you can brush on a heavy coat.

If you let the water base dry for perhaps a week, then you can brush on the dope without the lighter coat.

I'll post pictures of water based coloured, top coated with clear. In this picture, it's a small "Wild Thing" that I was a hurry to paint after a major repair. I only let the water base dry for a few hours, then hit it with dope....and it went a little "crinkly". Not great for a perfect finish, but in this case it was ok.
Another picture will show my Blue Flame. The water base blue paint, top coated with Sig clear is outlasting the plastic on the wing.
John
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Old Mar 20, 2013, 02:02 PM
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Fuel proof the water base paint with Sig clear.

Water based paints and dope or lacquer (solvent based)- how do they work together? In some cases perhaps not very well, in others they may be acceptable. You have to decide.

And again....this will never come close to dope and silk.....but it is a lot cheaper.

The following examples are not meant to be things of beauty, but examples of what has worked in the cheaper paint department.

For Doculam and mylar you may want to stay with coloured tissue and a top coat of Varathane, or you may want to paint instead.

So, above, I have tried the gray primer water based paint. It sticks.
and the Varathane sticks very well, maybe the best.

In answer to PR's question, is it fuel proof? Well, these are examples of water based paints covered over with Sig dope.

Just look at the paint and ignore the rough spot repairs. If the paint lasts 10 years, I guess it is almost fuel proof.

Will mylar and Doculam hold up with paint? Only time will tell. I think the "trick" is going to be getting the paint to stick. Maybe using Varathane and white tissue, then painted over the tissue would be the way to go. I don't have time for this now, maybe some one else can try.

Has anyone got a picture of the UH glue sticks that were earlier mentioned?

And why all this fuss and muss now? I just had to try this "new stuff" (to me any way) Doculam. Mylar, I haven't really used it, instead I have used clear "food grade" wrap on in door models. The mylar is lighter.
John
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Old Mar 22, 2013, 11:52 AM
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The above covers off, is it fuel proof.

Now for the glue sticks.

This site has a wealth of information and may be of interest to all.

UHU glue sticks information may be found here,

http://www.uhu.com/en/home.html

and interactive advice such as the king of material you want to glue may be found here

http://www.uhu.com/en/glue-advice/in...e-advisor.html
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Old Mar 23, 2013, 10:41 AM
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Mylar over top of tissue tissue

Here’s another “test strip”.

The balsa frame work is covered in silk span that has been attached using diluted WeldBond white, water soluble, glue.

One section of the silk span has been coated with Varathane (in place of dope).
In this case, the “water” allowed the silk span to loosen up and sage.
Result: while “wet” , both sides touched, the Varathane dried, and both sides (separated only about 1/8th inch) stuck together, then dried attached.
This wouldn’t be a problem on a larger frame work, or if the sides didn’t touch.

Note: A heated iron will also “iron out” any wrinkles or edges that are not stuck down.

Another test, mylar has been applied over the silk span using Weldbond and a hot iron.
This procedure will save having to paint and fuel proof the surface, since only the mylar (could also use Doculam) is exposed.

Note: the left hand balsa test section where I intentionally pull up the materia’s edge to detach the mylar is very well attached (stuck down to the frame work), but you might want to use one of the UHU glue sticks instead. This would avoid having to use a hot iron is attach the mylar.

The blue tissue examples, random strips applied to frame work, are stuck to the top (outer surface) of the mylar ( or Doculam if that’s what you use) using clear Varathane. They won’t fall off!

Tissue over mylar, attached with dope or Varathane is what SD and CB have used on the TomTit bipes.

See: http://www.rcgroups.com/forums/showthread.php?t=1773757

I’ll try another test for applying the clear material (Doculam) over the tissue using a larger surface such as my old Flight Streak wing shown on post #13,

http://www.rcgroups.com/forums/showthread.php?t=1804015

If we are looking for functionality (fuel proof surface) and not a thing of beauty, this may suffice.

Does anyone have examples that they will share with us? Please post.

John
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Old Mar 23, 2013, 11:15 AM
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Painting Doculam was discussed several different times in years past in the Scale Electric forum. If I remember right, Charlie from Manzano Lazer said that prepping the outer surface of the Doculam with vinegar brought very good latex paint adhesion. I wish I could remember which thread that was in so that I could post a link, but I gathered at the time that he uses that method regularly with good results over the life of the model.

Not much of a contribution, but another thought for consideration.

David
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Old Mar 24, 2013, 01:13 PM
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Thanks David.
Another "test" I'm trying is on my old Flight Streak. I'll recover the wing with cheap tissue and use Weldbond diluted glue to attach it with.
I'll use a hot iron to flatten out any wrinkles and "stick" the edges down.
Lastly, I'll cover it all with Doculam.
The Doculam already has the glue and sticks well.
The tissue will not require any Varathane or dope, as it will be under the top layer.
John
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