Let me toss in a few more things about dope that have not been covered, and maybe a bit about covering. The following is not from my "expertise" in using dope, silk, silkspan, nylon and now polyester, but is taken from the Randolph/ poly fiber manual. The manual recommends glueing fabric to the airframe. Of course we are not going to glue our fabric, but use dope to attach it. And we are not going to get into the plane and fly it. But, if using polyester fabric which Brodak and others sell, after putting 3 to 5 coats of NITRATE dope on the wood, thinned 50/50, attach the polyester with NITRATE thinned 50/50. After it is shrunk, which is (on a full scale aircraft) done with a calibrated iron at a specific temperature, the temp I do not have available, not a heat gun, you MUST brush NITRATE dope onto the poly until it is entirely encapsulated. Butrate will not stick to polyester fabric. I learned this the hard way when I thought I'd be slick and spray the nitrate on. This was before I got the manual. But, when I sprayed the butrate, holes developed in the paint down to the fabric. The more I sprayed butrate, the worse it got. Randolph is the only dope that can be used with poly fiber according to the FAA. No other brand of dope may be used over or under the Randolph dope. Stitz has another dope to be used with their poly fabric that cannot be mixed with Randolph. This according to the FAA. I have also been advised that Poly Fiber and Stitz are the same product and have just had different names applied to them. The polyester fabric sold by Brodak (the only poly fabric with which I have experience) appears by sight and feel to be the same thing as Poly Fiber, only much lighter. Now for the personal stuff. Up until a couple of years ago, I never used nitrate dope. I never used poly fabric either. All silk and butrate. I used Aero Gloss (AKA Randolph and Brodak). The old stuff had some taughtening. The new stuff has to be bought to specifically taughten. Only non taughtening dope can be used on Poly Fiber. Randolph sells both taughtening and non taughtening. I believe Brodak's is non taughtening. The taughtening stuff is tinted. I can tell you nothing about Sig.
Hope this helps. The manual is in my truck if any one needs any more info. I don't get into this computer on a daily basis, sometimes 3 to 4 weeks pass, but you can E-mail me and I will respond when I get into my E-mail.
Or... you may think I'm full of it trying to play expert, which I can assure you, I am NOT.
Bob