polyurethane for filling in balsa grain
I have used water-based Polyacrylic - by Min Wax - with corn starch added and it is excellent!!!! Unlike dope, there is no odor. I suggest you put a coat of the Polyacrylic on without the corn starch first. Then a second coat with. Add enough cornstarch or the Polyacrylic to make it a little thicker than cream. This is a very hard material when dry so don't be afraid to sand initially with a coarse sandpaper - like 100 or 180.
RCPAUL