You have to start off with your surfaces as smooth as possible. I sand out with P80, then progress through P120 and P180. Depending on the wood species I will sometime go to P240. I then pore fill with WEST Systems epoxy. Let sit for 24 hours and then sand back with P180, then P240.
Most woods will only require this done once, but I've had to do it twice on Australian Cedar to fill very deep pores. I will then wipe on a coat of epoxy thinned 50/50 with metho. just to give all the wood a uniform wetting. Let dry for at least 24 hours. I usually do this and then go on to other parts of the build. The epoxy protects the body by firming everything up and it doesn't hurt to leave it.
When it comes time to spray, I will just give the surface a "tickle" with a fine soft sanding pad or P320.
I use Mirotone catalyzed lacquer and thin it about 60/40. I don't want to spray on a heavy finish, and thin coats will give you really good results without a heavy build. Spray about 5 coats, letting the surface flash of at least 5 minutes between coats. 10-15 are better if you can. In high humidity and cool weather the surface might take on a blush, looking sort of milky. Don't panic, this is just moisture getting trapped in the finish. By respraying in more favorable conditions the milkiness will disappear.
Now let dry in a well ventilated space for at least 1 week. You can tell if it's dry by smelling the surface. If you can still smell solvent leave it to dry further. You will never get a great finish by rushing the refinish schedule.
Here's probably the most critical part. You can only level out a paint finish with relatively coarse sand paper. For lacquer that starts off at P320 or P400 if the surface is exceptionally good. So start with P320 dry. I like to use a foam/rubber block that you can get from the automotive supply store. Whatever you do, don't use a hard wood block or similar. If you pick up a small bit of grit under a block like this, it will make a deep scratch that is really difficult to get out.
You need to use dry paper because you are going to be inspecting the surface as you sand, looking for the shinny spots to disappear. You will have to make a judgment call here on whether you can continue to sand so that all the shiny spots are gone, or perhaps some deep ones will need to be drop filled.Maybe the lows are really tiny and will be taken care of in the next spraying. Again, don't panic if you can't get the surface perfect in this step.
You don't want to sand through to bare wood here. Stay away from edges, as it's really easy to take too much off of them. They some how manage to get just the right amount done to them, by not trying to touch them.
Now you can sand with P400 and perhaps P600 if it looks like you aren't going to cut through. Then spray another 3-5 coats just like the first time, and let sit for at least 2 weeks. Most times I get away with only 2 sessions in the spray booth, so I'm trying to get this finish pretty good, so I won't have much to do after it comes off the gun.
You're going to be leveling the surface again, but hopefully you've done a terrific job to this point, so it won't take much work. This time I start with P800 wet and level out the finish. I wipe the surface back regularly with a dry cloth and inspect in a good light. I stop sanding as soon as I get a nice even surface.
If everything looks good, you can proceed on to the next steps. If there are still some imperfections, you can spray a few more coats and then repeat the previous sanding step and then move on from there.
Then I proceed on with P1000, P1200 and P1500. These grits do not level. They only refine the scratch pattern left by the previous grit. You could start buffing after the P800, but it would take ages to get a glossy finish. It doesn't take much sanding with each grit to get to a surface that will buff up easily.
I use a automotive foam buffing pad that I've modified by finding a bolt with the right thread and cutting off the head, then mounting it in my drill press.
I have the speed set at 1350 RPM for this size pad. If it was a large pad then I would drop the speed down to 900-1100 RPM. It's the outside edge that does the work, and the damage, so don't take a nap when doing this.
A little polish and light to medium pressure. Let the pad and polish do the work. Remember that lacquer is themoplastic, so if you get it to hot, it will melt and get dragged with the buffing pad, then you will be learning how to do a spot finish repair
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This guitar took just 2 hours from start to finish including the neck. Thats sanding from P800-1500 and buffing, then finishing up with a soft rag.
