I've recently embarked on my own guitar project and all is going well so far, however I'm a little confused about the whole grain filling and clear coat process.
I have applied a Walnut veneer to the top of the body, but does this now need to be filled?
Yep. Walnut has open pores in the grain, much like mahogany (and ash, and Spanish cedar). There are tons of things you can use for pore filling, but I’m a fan of Z-Poxy resin. You can get it here.