Trying to play guitar and plectrum banjo using Wes Montgomery thumb technique. This technique uses the fleshy outer edge of the thumb to contact the string, not the fingernail. Also it does not use a thumbpick.
Problem is, I've just started this technique and it's going to take awhile to build up the callus on the side of my thumb next to the thumbnail.
How can I play for extended periods of time with both downstrokes and upstrokes using the edge of my thumb before I build up the callus?
I feel your pain. I've been playing for over a decade now using primarily my thumb (example) and I'm sorry to say there's nothing you can do but start slow.
The issue is that the motion of picking introduces a shear that will quickly wear away any coating, material, or other expedient. Much less the skin. It's like building up the calluses on the fretting hand, but worse. It takes a lot of discipline to stop even before you feel discomfort on the thumb, then gradually play a bit longer each day. I've also found that you lose the thumb callus way faster than the ones on the other hand if you don't play regularly.
Some advantage (minimal, but it's there) can be gained by using lighter strings. Even a bit more with nylon strings. But the answer to how you can play for extended periods without the callus is simply pain.
