Now that the fretboard is finished, it can be glued on the “neck”. For this you need five to six clamps and a piece of wood slightly smaller than the fretboard to serve as a clamping caul. A caul is recommended because it distributes the pressure of the clamps evenly.
Apply a thin, uniform glue film on the back of the fretboard. I do this with my little finger so my other fingers remain clean. Place the board on the plank and butt it up against the nut. Then put the caul on top of it and tighten all the clamps a little. Increase the pressure on all the clamps in the row until they are all fully tightened. A clamp should ideally only exert downward pressure when tightened. There is, unfortunately, almost inevitably some other force involved which makes the fretboard move on the slippery glue coat. You can minimize this by clamping small pieces of wood to both sides and to the end of the fretboard. If you notice that the fretboard has slipped out of position and can no longer be moved, remove the clamps and the fretboard immediately, scrape the glue off carefully and start all over. I had to do this twice on this guitar until I discovered that it helps if you tighten every other clamp in the opposite direction, as shown in the picture below. Wipe off any glue that has been squeezed out with a damp rag.