Originally Posted by
jester_s1
Spackle will probably be fine on hard sheeted surfaces, but will crack if used on an open area. Nitrate dope with some baby powder mixed is a classic filler, but it will have to be sanded after. Water based polyurethane works decent too.
DO NOT sand fabric over an open area if there is any way to avoid it. It doesn't take much pressure to stretch it and create a sag, and it's really easy to cut through it at the wing rib. Very light pressure to remove a run can work, but it's a pain.
Yes, nitrate dope and baby powder is a classic and time-tested filler (smells good too!), but he would first have to check the dope's compatibility with the primer already laid down. Nitrate can receive almost anything OVER it, but not all finishes can accept Nitrate applied ON them.