Originally Posted by
Simon Barden
Well you won't need grain filler with basswood, it'll just be a waste of time. But a sealer is recommended.
Certainly get the body as flat as you can before applying paint, though you really don't need to go above P180 or maybe P240. The main thing is to get rid of all the bumps and dips so that the whole surface of the body is flat (except for the curvy bits of course, but even they should be smooth with no high and low spots).
If you can start with a mist spray of the sealer, then if that shows up enough to be useful, you can use that to see all the dips that will need sanding down to. If not, a very light mist spray of a paint colour, just so that you can see where you've been when sanding. Sandpaper (from a roll) stuck to a flat piece of wood with double-sided tape is best for this. One that's longer than the body. Once all of that mist coat has gone, then you should have got a nice surface to start from.
Incidentally, what I've found out very recently is that the sanding' in 'sanding sealer' just means that it can be sanded, as opposed to a 'non-sanding sealer' which is meant to be applied thickly and not sanded at all. Its purpose is to seal the wood and stop the finish on top from sinking in. It may take two or three coats of the sealer to do this properly, especially if you sand back significantly (and so expose untreated wood). But it's far less coats than you'll need to get enough finish on for a level surface after sanding once the finish has stopped sinking in.
You can get the surface of the wood very flat and smooth, running through the grits up to P2500 if you want, but that won't stop you getting an orange peel surface that needs sanding back smooth and polishing. That's all down to the paint, the spraying techniques and the spraying environment. I don't know enough about the different paint types to know which ones prefer a slightly rougher surface to stick to. But even PRS don't go to very fine grits to get their wooden bodies ultra-smooth before adding the finish. That's all saved for the finish layers.