Very interesting thread for me. thanks to everyone for the informative posts. I want to phase out dope, which is what I've used for most of my planes all my life. I don't like the fumes, and now I have a shop attached to the house and I want to be able to finish planes in the winter when I can't take them outdoors.
I'm rebuilding a crashed Big John bipe and trying several experiments with materials that don't make noxious fumes. The thread is here...
http://www.rcgroups.com/forums/showthread.php?t=2589155 It is attracting just about zero interest so I will report on finishing here instead.
On balsa-sheeted foam cores, I applied Polycrylic directly to the wood. The wood is bonded to the cores with Gorilla Glue and I am certain it will not warp. I found it takes 3 coats to seal the wood to the point where I can cover with other materials. Pc raised the grain, but no more than dope does. I just sanded lightly with 320.
I used glass on the center section, for strength in the dihedral joint area. I put it on with Polycrylic. No mess, easy to apply. Then I used strips cut from a paper bag to simulate ribs and applied with white glue. Then I put silkspan over each entire wing using Polycrylic. It looks fine so far. The silkspan/Pc surface is far from smooth, but I do not plan on a show finish. If I did, I would mix Polycrylic with talc and put on a few more coats. For this old airplane I'm more concerned with weight than with a fine finish.
I built the ailerons from 1/16th inch balsa sheet and 1/8 sheet ribs. No core, so I was concerned about warping the wood using wb. I sprayed on two coats of shellac from a can, then Polycrylic, and then silkspan like the wings. I have no warps and it all looks good. Maybe the Pc would not have warped it, but I didn't take the chance. Nice thing about shellac is that it is alcohol based, so no dangerous fumes, yet no water either.
My plan was to put down a white primer, either Glidden Gripper or Nelson white primer, haven't decided which. Then I'll take a part of the crashed plane to Home Depot and get a color match in Behr latex, paint the wings and then clear coat with System 3 clear.
I'm not so sure about that last part now, because the fuselage and tail are all doped and I'm concerned that the look might be too different. I will definitely use a wb primer, but I still might go with dope one last time for the final coat, just so it will match the rest of the plane. I figure the dope will not attack the foam underneath because there will be so many coats of material protecting it.
Any thoughts, guys?
Jim