I got some of the red bondo stuff and it works ok, just alot of extra sanding.
You can't get away from sanding, no matter what you end up doing with this hobby.
Unless, of course, you don't bother painting at all, and don't care how your rocket looks.
3M Bondo 907 sands way easier than either epoxy or CWF, and dries quicker than both of those. So that's what I use 99% of the time these days.
I also got some of the 2 part epoxy clay that tim Milligan recommended but it doesnt stick well to estes tubes at all so I'm left with the thick auto primer.
TVM's epoxy clay is only good for, and sticks well to, inside of trash cans. It is an absolute crap of a product (there are always better alternatives for every single use case where TVM pitches it). I speak from experience for haven fallen for the sales pitch myself, many years ago, and having junked it.
It must be a pretty high margin product, given how hard he pushes it.
Is it possible to apply fins on a regular estes lpr kit after painting with primer?
As other have correctly stated - absolutely yes!
Just scrub off the areas of the body tube and the fins (you did prep and paint fins as well, right?) where the glue will be applied, and the glued joint will be perfectly strong.
If you want to be a perfectionist, sand off some extra areas around the fin attachment points to leave room for fin fillets as well!
For example (picture below):
- airframe had spirals filled with Bondo 907, sanded, sprayed with sandable primer, sanded. Then areas where fins were going to be glued in were sanded back down to bare paper layer.
- front fins below have been papered, soaked in CA (for extra strength), sanded near smooth, sprayed with sandable primer, sanded (cycles repeated until I got them perfectly smooth).
- aft fins were constructed out of balsa frame and paper skins, then "painted" with epoxy (for serious extra endurance), sanded, etc.
Once I attach the last FWD fin, I will move onto applying (epoxy) fin fillets.
Then goes another layer of sandable primer to fill any imperfections (maybe some more Bondo 907, if necessary).
Then paint basecoat (color TBD).
Then paint highlights (colors TBD).
HTH,
a