Sand through? Ummm... Teak oil is not a finish that builds. If you are building a finish with teak oil you are doing it wrong. Teak oil has varnish and dryers in it. It is not a film finish. It is meant as an oil finish for oily stubborn woods not as a film finish. Yes. And this season coming up no. I use oil finishes on the woods that can handle oil. Cocobolo, Bloodwood, Ebony, etc... as tops are great with oil. I think next year I am doing a bunch of tops that require gloss. Ziricote needs a gloss finish. Maple needs a gloss finish. For those I use Nitro. Just bought a new buffing rig that allows me to get a very professional shine on my Nitro. Makes me happy. As for the fretboards. I have had pretty good luck with Behlens fretboard oil or using Behlens Teak Oil. There is not a lot of difference between the two other than cost. Putting a oil/varnish mix on a wood that enjoys oil is ok. Put oil on cocobolo at your own risk. With the oily exotics I always have to use an oil with drying agents in it.