Well I don't know the fuel I use has lots of caster. And when I finish I use Silver xcide mixed with Butirate dope. Never had one fail. A few Of my planes are 45 years old. My most recient build is the Brodak Bi Slob. I used the same material its old Aircraft cotton with pinked edges I coat the balsa with 3 coats of nitrate. To fill the balsa for a smoth finish I mix talc with BUTIRATE dope. Then finish in silver. I tried using stits polyfibre finish but I went back to randolph. They supply to Sig And Brodak. Those just 9 dollar bottles. If I used color I would buy a Quart. Did buy a quart of yellow. For my wings. Just use the silver I know I am going to crash so why do a nice finish. Also much easier to repair. My planes are not pretty but I sure enjoy getting dizzy. AJ.