Finishing the neck after defretting, what a mess!

[JaneBass1]

I defretted the bass, put wood filler and was on the process of finishing with polyurethane.

I sanded after each brush of poly. Did 3. After the 3rd one I see some white patches, and it doesn't shine on those anymore. The shining is uneven actually.

So I thought I didnt sand it properly the 1st time, so I sanded off all the poly again and started from scratch.

I put 1 brush of poly this time. And left it there for 3 days. I sanded it with a fine paper, and I notice the same white patches start coming out. It's unnerving.

What the heck am I doing wrong. I am thinking to sand off the poly again, and just leave it as it is

[62bass]

What is the fingerboard wood?

I don't know what's going on there--could be oil, wax or resin in the wood, but with all the sanding I would think it would have been removed.

Try sanding off the poly again to bare wood. Then thoroughly wash the fingerboard with lacquer thinner or acetone. Wash it a couple times and let it dry.

Make sure your poly is new and hasn't been sitting around for a long time and getting partially cured in the container. Also check the sandpaper you're using. The "open coat" or "free cut" stuff has a soap like treatment to prevent it from loading up with sanding dust. Sometimes this can be a problem. The solution for that is to wash down the wood after sanding with mineral spirits or alcohol.

And do you know you have to apply several coats of finish before all the pores are filled?