I have my wing cores all sheeted, covered and slicked. The grain holdout is simply incredible with the carbon, much better than the silkspan (the carbon does not shrink). At this rate the primer will only be used as a sealer instead of a filler, since the surface is pretty much filled with the carbon alone.
The total weight of finish per core, from bare wood to a completely slick finish, is 1.2 OZ. That is 2.4 OZ of fill finish for the wing (700 square inch wing). This is similar to the weights using silkspan, but the silkspan wing required further filling and excess primer. I do not see the need with the carbon. I could keep sanding, but I do not think I will.
To say the surface is hard would be an understatement. Two layers of .3 oz Art's Hobby cloth is simply like sanding an Eather prop. Pretty incredible.
The method thus far is to rub one super light coat of straight PC on the wood (I use a paper towel) and let dry overnight. Knock the edges off with 180 grit. Mix PC, zinc stearate, and alcohol 2-1-1 into a "slurry". Use slurry for all carbon attaching (kind of looks like thin chunky mayo). Simply lay the carbon down and brush until filled. Let dry two hours. Check for bubbles. If bubbles (places that did not lay down well) appear, sand quickly with 180 grit and the area will lay down. Let dry over night. Sand with 180 grit. Add second coat of slurry. Sand with 180 and then 320 for slick finish (only use auto body open coat papers).
I know there will be responses to the effect that this method is too "heavy". My numbers show this finish to be lighter than Mr. Hyde (more filled at the same weight). Mr. Hyde is 64 oz all trimmed out. Even though Bobby Hunt thinks that is heavy (this is indeed heavy for a Ro Jett 40 plane), Mr. Hyde might be the lightest Impact sized Saito 72 plane around (Windy's Typhoon might have been lighter) especially for a foam winger (also too heavy). The goal after all was to be the same weight as PW's Impacts, and that goal was achieved. Now I am searching for the ultimate tough and strong finish (read that "wears like iron").
BTW all of the finishing so far was done inside the house with zero complaints by the wife. This is the true BONUS of any method using PC. Filling with PC, carbon, and zinc stearate allows me to further finish the airplane in the house with a brush, delaying the inevitable trip to the garage and the spray gun.
The City Smasher