Current project (scale) has a mix of fabric and balsa sheet covering.  On the sheeted panels, to hide the grain, what is lighter? Silkspan or filling with sanding sealer?

Gary

Well, there's always Bob Hunt's epoxy method. Paint on thinned epoxy to a sheeted wing the wipe it off the put filler on. Never tried it myself. I do silkspan and dope.

Over balsa, Japanese tissue is lighter, tighter fiber and needs less filler to be smooth than silkspan, Polyspan or Carbon veil.. Not, however, strong enough for open structures except for very small models.

In my experience, trying to fill balsa with just dope and fillers is hopeless. Each successive coat brings back the grain. Maybe if you leave a week of outgassing between coats that would not happen, but I haven’t that kind of patience.

I have been pleased with two or three coats of very thinned epoxy, sanded between coats to give “tooth” for the next coat. Mixing in some cornstarch really helps too! It is lighter, fills better and sands out more easily.

BTW, cornstarch is cheaper, lighter, less toxic than Talc, and absorbs some of th paint for a better bond. And you can swipe all you need from the kitchen and the little woman will never notice. 

Current project (scale) has a mix of fabric and balsa sheet covering.  On the sheeted panels, to hide the grain, what is lighter? Silkspan or filling with sanding sealer?

     I would just add a "me too" on the others - you will *never* get the grain filled with sanding sealer alone, and even acceptable results will take months of waiting to allow it to shrink before sanding and finishing.

    For scale, I would definitely look into sealing the bare wood with finishing epoxy before applying anything like dope to it, to stabilize the surface with something that only shrinks a little bit and very slowly. It would very nice to get rid of dope of any variety, but so far I haven't seen any acceptable substitutes for it in applying silkspan (although there are a bunch of very poor substitutes). The weight hit is negligible if you do it right (Bobby says it was about an ounce for a full-size stunt plane) which is not a problem if it's only in limited areas, and makes the finishing better and more durable.

   Note the "do it right" part - you aren't trying to fill in "one coat" with epoxy, you want to get good coverage and then remove absolutely every bit of it you can get to, no puddles on the surface or shiny spots. You want just enough to fill some pores and stabilize the surface with something that will not move when you put solvents on it.

     Brett