Hi guys,

Does anybody out there know how to use silkspan and dope method to cover an old timer?
Can you guys be very specific about this process?
(1) What kind of dope should I use over the balsa frame before applying silkspan? And how many coats?
(2) Any sanding once the dope dries?
(3) Should I wet the silkspan first before draping over the balsa frame?
(4) What dope (or glue) should I use to attach the silkspan over balsa?
(5) What kind of dope should I brush on silkspan once it dries for shrinkage?

Thanks a bunch.

it is very similar to glassing. if you've ever done that?
open wing process
Wet silks span with a spray mister, don't drown it. just so its wet but not dripping very much
Then lay over the frame work, working out the wrinkles, then with a brush apply the "Clear Butrate dope" along the ribs and leading/trailing edges, wing tips etc. as neatly as you can, just where tha silk meets the balsa, you'll see the cloth kinda diapear and the balsa show through. thats enough dope. let it dry. after its dry apply and coat of clear to the intire surface let that dry. Then paint it with the color dope of your choice. you may need to litely sand the fuzz off before the finial color coats.

Some guys use "balsa rite" as a primer/sealer before they start with the silk span or tissue & dope

Make sure you sand the balsa very smooth before you start 400 grit paper a least

It's been 30 years since I did a plane with Silk & Dope, hope I didn't miss anything

Good luck

I give the outside of the frame a cout of nitrate dope before applying the silkspan. Then dope through the wet silkspan to the outside of the frame (this softens the dope underneath, allowing it to grab better. Once all is dry I follow up with butyrate to shrink and harden the silkspan (remember to thin, at least 50/50 or your wing will resemble a propeller!)

Hope this helps!

You will get better results if you put at least two coats of nitrate dope over the structure to be covered first. Sand lightly between coats of dope. Place the dampened silkspan over the surface to be covered. Carefully pull out all wrinkles and unevenness then just brush on thinned nitrate dope over the structure where it is to be bonded. This will bleed through the silkspan, soften the dope layer underneath and bond the material. After the moisture has dried out, the surface should be reasonably tight. Now brush or spray a thin coat of nitrate dope over the surface, very lightly or the dope will puddle beneath the surface and cause some unsightly splotches. Let this dry then coat again. If you want it fuel proof, you need to cover the nitrate dope with Butyrate dope or a fuel proof finishing coat. In short, a lot of work that is subject to many pitfalls but looks really nice if you don't goof up along the way.

HMMMM... this takes me back a few... ahhh years.

If you dope the entire structure the dope will actually strengthen the balsa somewhat. This is more critical on very light wiegth frameworks. Lightly sand structure before covering. Lightly wet span out pulling any wrinkles out and dope the leading and trailing edges. Dope thru on ribs that are undercambered to get the silk to stick and It will take 2 sometimes 3 coats coats of 50/50 thinned dope to fill the silkspan and if you havent used colored silkspan then colored dope after the fill coats. Its a good idea to weight the frame work down if you can to prevent warps or if your trying to set in washout make sure the proper shims are set under the tips to create your washout.
Try not to dope when its humid or use a little retardant to slow down the drying process. Humidity will make it get a foggy look.

Loved the smell of that stuff... no wonder momma thought I came up a little starry eyed when building. heh! heh!

I still use nitrate dope to fill balsa or harden it before covering or glassing, even use it when sheeting foam wings. It seals the pores and does not allow the wood to absorb to much resin or glue.

can someone specify WHAT to THIN the dope with?

THNX in advance for the info

You can buy dope thinner from Sig and I'm sure other sources. It is called "Dope Thinner". I'm don't know what the chemical make up of it is.

Rodney,
I have read in a UK magazine article that one can dilute DOPE with gun-wash... don't know what it is!? Where can I get some?

Dope thinners is generally acetone, with perhaps some small amounts of additives to slow the evaporation rate. The bottle on my bench lists

Acetone, 80%
Toluene 5%
Gasoline Spirit (?Kero?) 2%
Methylated Spirit 3%
Other hydrocarbons 10%


I get the idea that the thinner is designed to evaporate just a little quicker than the solvents in the dope. In the case of the thinners I've got, the contents look pretty much the same as the dope recipe with the exception of the cellulose acetates.

I have heard of people using lacquer thinners as well, but my one (disastrous) and only experience with that will never bear repeating. I the stuff I bought apparently contained a plasticiser for the lacquer.

So, there ya go...that is what my dope thinners has in it.

I use the .wet the silkspan and blot it on a towel ,method and apply over a twice doped frame and use thinner through the fabric to adhere it to the model. I use laquer thinner to thin nitrate dope and to apply silkspan. Laquer thinner will curdle the color in dope but works fine with clear. I have used "deft" wood finish instead of dope on my electric airplanes which do not require fuel proofing. Silk span can be applied over foam using thinned elmers glue but this again is not fuel proof! Jim Finn

Dope thinners are a ketone, I think I spelled that right. It doesn't dry as fast and lets the dope flow so it smooths out.

Silkspan does have a grain. To find it just tear a little corner to see which way the tear will run. The direction it runs will determine the direction you put it on the wings. The tear should go lengthways to the wings. Going the other way will create concave curves between the ribs of the wings when it dries.

Thank you, all.

Great replies.

One more point though..

Most silk or nylon covering has a slight 'grain' to it. That is, it stretches better in one direction than the other. Make sure the stiffer grain direction is placed span-wise, and you pull the covering more in that direction as you are laying it on the structure. It should reduce the sagging between the ribs.

-DC