100% before the fins, unless I screw something up (e.g.: wanted to apply vinyl wrap, had to give up on that, now have to go back and fill those #$%^ spirals).
I'm using the following, sometimes interchangeably, sometimes depending on the depth of spirals involved.
Listed below are the options in the order in which I resort to them as of this season:
- 3M 907 Bondo Glazing & Spot putty.
- Pros: inexpensive, quick and easy application (squeeze out of the tube), dries quickly, easily sandable.
- Cons: a little stinky, wasteful in application on shallow spirals (hard to apply small quantities).
- Paint primers, Krylon Industrial Tough Coat (KITC) in particular.
- Pros: inexpensive, dries quickly (unlike other primers), sands VERY easily, doesn't clog sanding paper (true for KITC, not true for other paint primers). KITC has a rubber-like component to the paint that fills spiral valleys way quicker than other primers.
- Cons: a little stinky, requires multiple (3+) passes to "build up" enough material in the spiral valleys. Can't be applied precisely, thus requires more sanding cycles.
- Tamiya Putty(white).
- Pros: the easiest to sand, dries quickly, can fill-in 1/8" of a valley in one pass.
- Cons: expensive, comes in small 32g tubes. Impractical for large airframes.
- Elmer's WoodFiller(white).
- Pros: cheap, can be dissolved with water and "painted" into the spirals.
- Cons: requires multiple (3+) passes to "build up" the filler in the spirals. Takes a while to dry. Can be hard to sand. Doesn't stick to glossier tubes, and will fall out during sanding unless you pre-sand the spiral valleys before application.
- HobbyLite balsa filler - not anymore.
- Pros: cheap, can be dissolved with water and "painted" into the spirals. Easy to sand.
- Cons: requires multiple (5+) passes to "build up" the filler in the spirals. Far too fragile (falls out of spiral in chunks), doesn't stick to tubes all that well unless you pre-sand the spiral valleys before application.
For shallower spirals I go with #2.
For deep spirals I go with #1.