"Buried" Frets
Raising the dead
Smack a fret too hard, and you can actually drive it below the surface of the fingerboard. That's what happened to the fret under the 3-28/32" mark on my 6" rule below:
Pulling the fret out, I can see the depression in the rosewood fingerboard:
Now, the cure for this problem can take a couple of forms. If I were refretting n instrument and accidentally drove a fret in this deep, I'd pull out whatever frets I'd installed, and resand and level the fingerboard before finishing the job.
One of the reasons I like my yellow faced plastic hammer is that it is virtually impossible for me to have an accident like the one above! The plastic face limits how hard I can tap a fret.
For an inexpensive instrument which might have been manufactured carelessly, or to repair a fret that had been hit when the instrument fell off a stand and smashed into an amplifier, I might choose to raise the fret without actually replacing it.
In that case, I'd grip and lift it with my fret pulling pliers:
I'd lift it as little as possible, trying not to let it come out of the slot completely.
Then I'd tap it back with my little steel plate and a light ball peen hammer:
The steel plate would keep it from being driven below the level of its neighbors.
I could also use my little rigid steel rule, being careful not to hit it very hard:
Once the fret was back level, I'd run some thin viscosity cyanoacrylate underneath to hold it in place. The meniscus of glue under the fret crown would act as a sort of shim to "bed" the fret securely.