I have always used oak for my necks, and at first I was always frustrated that no matter how well I sanded the wood, the oak's open pores meant that the finish was never completely smooth. After a bit of research I came across grain filler, and ordered a tin of Rustins.
Grain filler is different from wood filler, which is used to fill larger voids in wood. It comes as a thick putty which you thin down with white spirit (mineral spirits) or turpentine to the consistency of cream. You then apply it to the grain of the wood and it does a pretty good job of filling in the pores. I use the 'natural' version for oak, but they do other shades for darker woods etc.
First off, get your neck sanded down as smooth as possible. I do mine up to 320 grit at this point. Then give the neck a wipe down with white spirit to remove the wood dust.
I apply the grain filler all over the neck with my finger, rubbing it lengthways into all of the pores. Once the whole neck looks done I leave it to dry overnight.
This is what you see after the grain filler dries out. At this point I just lightly rub the excess off the surface with my thumb until I see this:
The pores are now filled in. Now it's time to lightly sand again, starting at 220 grit and working up to 600. A quick rub down with white spirit again and you're ready to start applying finish.
As you can see, the grain filler does a really good job of blending in with the wood tones.
The same neck after an additional 6 coats of Tru-Oil, then a final 1200 grit wet sanded coat a week later. Lovely and smooth! I hope this helps.
-Richey Kay
