Just wondering what procedure is best for eliminating the joint line between two pieces of balsa from showing through the finish after a period of time.

ambroid shrinks just like dope does,,and as such it will come back,,,, titebond and a GOOD fitting joint is your best bet IMHO

Just wondering what procedure is best for eliminating the joint line between two pieces of balsa from showing through the finish after a period of time.

How long a period of time?

Charles

I have this problem, even after lots of help from Bob Hunt, both on the phone and in his video.   I think I have been squeezing the joints together too hard.  They form a peak which gets worse with sanding.  I backed off on the pressure squeezing the joints together on recent projects, and the joints seem to be better.  I had a bad case of this problem on a wing of last year's dog.  In desperation I built up the area on both sides of the joint with dope and zinc stearate.  Sanding that carefully fixed it.  Finally, I made sure the peak wouldn't return by running the wing into a traffic cone on takeoff. 

Although it seems unlikely, I've made very good butt joints with 1/16" balsa by using thin CA.  I cut the ends to be joined on an angle to avoid a  stress riser, pressed them firmly (but not hard) together, taping along the seam, and flipped the assembly tape-side-down against my wax-papered table surface. I light-sanded across the seam (keeping it beneath the sanding block/bar) and then dragged the fine CA applicator (blood pipet) along the seam. The CA permeated the immediate area without puddling on the surface, but a quick swipe with a paper towel seemed a good precaution. The seam usually set immediately ('can use accelerant), allowing an immediate light sanding across the seam, which did not take just the balsa down along the seam, as might be expected. One fuselage like this was covered in doped glass cloth and never revealed the line. Two others covered with epoxied fiberglass and naturally did not reveal the line. My original P-Force kit fuselage, with it's thicker, joined, fore and aft sides, was also assembled this way and covered with lousy modern silkspan, but it's seams never showed over several years.

Here's one of the profile-fuselage sheeting joints. I'm sorry that I don't have a photo that reveals the smooth surface well, but you can see the arrangement. Mike Alimov showed me this method years ago, and it has always worked - no visible seams  after finishing, despite mismatched wood.

FWIW, here's what you get with immediate gratification - the instantaneous, strongest bond with the least force concentration and no seams showing. These two fuselage pieces were finished over 12 years ago and have set outside in the hot sun and cold on numerous occasions over the years. The only blemishes are dents from our 2013 Christmas tree stand leg. I've set the pieces next to the plan, so that you can see where the fore and aft fuselage pieces joined on each side. That's a doped finish, using the crappy modern silkspan and tautening Brodak Butyrate dope without retarder.

I use polyurethane glue when I vacuum bag my balsa sheeting over a solid foam core.  No need to glue the skin sheets together.  Just tape them tight and the expansion fills the seam.  Never had any issues.  Never liked it though for general gluing as it's too hard to control where it goes.  And, I'm not particularly fond of how it sands.