Originally Posted by pd1

Here's a couple of things I've found out about silk and dope.

Nitrate can't be applied over butyrate. It will react and ruin your finish.
Nitrate is very flammable compared to butyrate.
Nitrate has a little better adhesive qualities compared to butyrate.
Nitrate requires additional fuel proofing.
Nitrate stops shrinking after a couple of days.
Butyrate shrinks for a long, long time.

Covering. I don't use nitrate anymore, personal preference, so to increase the adhesiveness of the butyrate I coat the bare structure with butyrate until the wood picks up a shine.

Then apply my silk. Spray the silk with water and get the wrinkles out.
I use a lot of thinner with just a little dope to stick the silk.
The thinner passes through the silk and softens the dope underneath sticking the silk down.

If you accidentally get some of the thinned dope on the silk, there is not enough dope to curl the silk.
Thick dope will curl the silk as it drys.

Using dope while the silk is still wet will cause the dope to blush. It will actually turn white.
Let all the water dry off the silk before doping too much.

If it is a day with high humidity, the dope may blush again. A couple of drops of retarder will stop that.
Sig sells retarder in small bottles.

If you hold a wing horizontal while doping, especially with dope that hasn't been thinned a lot, the dope will drip through and make an ugly ''ring'' on the other side of the wing.

To avoid that when doing wing panels, just use very thin dope and hold the surface vertical.
The thinned dope will not leave a ring, and if the panel is vertical the dope will stay on the side you are doping.
On the last couple of coats of clear I add a couple of drops of Castor oil to the clear dope. It will act as a plasticizer and will slow dope from drying out over a long time.

Silk. I've found that there are at least two different silks that shrink different from each other.
The silk from Thai silk seems to be pre shrunk and doesn't shrink much if at all after covering.
This is good for delicate structures.

http://www.thaisilks.com/product_inf...22fba3399425a4

The silk I like from there is the 5mm 021F-000 Habotai.

If you want silk that shrinks more, the silk from Dharma Trading is for you.
It's great for stronger structures.

http://www.dharmatrading.com/html/eng/3374-AA.shtml

I use the 5mm. HS536 or the HS545 same but 45 inches wide.

I've found the 5mm silk is lighter than any other covering, including tissue and the weave is so tight that it doesn't take much clear to fill.

Before you ask,mm is not milimeters. ''MM is Momme.
Momme (pronounced ''mommy'' and abbreviated ''mm'') expresses the weight in pounds of a piece of material of size 45 inches by 100 yards. So, for example, a 50 yd. bolt of our 5mm 45'' Habotai Silk fabric (#HS545) would weigh 2.5 lbs. (plus the weight of the cardboard tube it is wrapped around, of course).
The higher the momme, the heavier and stronger the fabric. Anything above 28 momme is considered heavy-weight and generally used for curtains or heavier outer-garments. Silk under 20 momme is considered lightweight, and generally used for light blouses with a chiffon feel. Medium-weight silk (20 to 28 momme) is excellent for silk scarves, furnishings, wedding dresses and the ultimate luxury of silk sheets.'' Dharma Trading.


5 mm silk is extremely light.
A sheet 45 inches wide by 300 feet long would only weigh 5 pounds.

Drying out and rot. Unless you leave the silk in direct sunlight, the silk won't rot.
What actually happens over time the dope becomes hard and brittle. The silk is saturated with the dope and when the dope cracks, so does the silk.
I just started removing silk that was applied 40 years ago. The silk is fine, the dope isn't.

Silk has a "grain" to it. It usually has a finished edge on one side of the piece. The grain is parallel to that edge.
Run the grain spanwise on a wing across the ribs.
If you run the grain chordwise, with the ribs, the silk will pull down between the ribs and look odd.
Silk shrinks more with the grain than across it.


If you thin dope sufficiently, and use a good brush, it will not leave brushmarks.
I use a camels hair brush, most hobby shops carry them.

Originally Posted by buzzard bait

Truckracer, yes, I save money buying from Wick's. Also, I understand red Sig is more of a dye than a pigment, whereas Randolf is a pigment and covers better.

.

Originally Posted by buzzard bait

Les wrote something very important...there are tautening dopes and non-tautening dopes, and that is true of BOTH nitrate and butyrate.

I think Sig gave good advise about the butyrate. Litecoat has an additive to make it non-tautening. Unfortunately Sig does not say as much as you might like. Is Supercoat entirely free of non-tautening additive, or just less than Litecoat? They don't say. And their nitrate says nothing at all.

Thai Silks pre-shrinks all their silk. I thought that Dharma did not shrink the white silk. In any case, by the procedure below even pre-shrunk silk will work if you start with tautening nitrate, but barely. I have not tried Sig Supercoat as the initial coats.

Avionette, I'm sorry to hear of your problem, but it might not be fixable at this point. The only hope would be if Wick's or Aircraft Spruce has something that tautens (tightens) more than Sig Supercoat. You could try their tautening butyrate and add three more coats to see what happens. Three coats is not very much, so more coats might help.

Jim

My experience with Thai Silks, 8 mm Habotai, was this:

1) Purchased TAUTENING nitrate dope from Wick's Aircraft Supply. They sell tautening and non-tautening, clearly labelled.

2) Doped structure with tautening nitrate.

3) Applied Habotai silk wet, getting it as tight as I could.

4) After drying, doped with thinned tautening nitrate, three coats. It worried me at first, but after a day of drying it was tight enough. Not super tight, but it looked and felt good.

5) After 3 coats of tautening nitrate, 3 coats of Sig Supercoat. I should have used a couple more.