Originally Posted by
Simon Barden
Don’t sand the shellac. You are building up protective layers of shellac between the stain and the clear coat, so the clear coat only touches the shellac, not the wood. If you keep removing the shellac by sanding, you defeat the whole purpose of using the shellac.
Yes, you want a dust-free environment, or at least a still-air one. It is always best to spray outside if possible as any aerosol paint spray is bad for you. But any separate space like a garage or shed is fine. I made up a wooden frame to hang my guitars from for spraying and used a pop-up toilet tent to spray in. Others have used portable fabric-sided clothes wardrobes (these come with a hanging rail built-in). I close the flap immediately after spraying for 5 minutes, so the surface hardens enough to not pick-up dust, and then open the flap for ventilation and to help prevent heat build-up. If you have a suitable room for spraying, you can get lightweight clothes hanging rails on wheels that go high enough to hang a guitar from. If you have a wooden beam in a garage or out-building, you could use a screw-in eyelet to hang the guitar from using stiff wire or thick string.
I generally use a big stainless steel S-hook intended for hanging up kitchen utensils to hang up a guitar by a tuner hole. It needs to be big enough so the curve of the hook only touches the tuner hole at the very edges so you can spray behind it on both sides of the headstock.
Or you can use a screw-eye in the rear strap button position (make sure the screw thread is a bit smaller than the strap button screw that will replace it) to hang it upside-down.
Others have used a G-clamp that’s clamped between the two pickup routs to give them something to hang the body from.
I started out using a boom microphone stand, but the boom arm often sagged under the weight and as it sags, the guitar moves away from the central upright, and the stand becomes unstable and can topple. Whatever you use to hang from needs to be stable.
But you need to be aware of the temperature. You really don’t want it below say 15°C or above 30°C. And in the sun my toilet tent gets much warmer inside when closed-up (my first tent was dark green and got really warm but my current one is silver/white and reflects a lot of heat).
You’ll probably want six good coats of clear before proper sanding.
Follow the manufacturer’s instructions for re-coat times. I’m more familiar with nitro, but the acrylic clear spray I used recently was within 30 minutes or wait 24 hours with a very light sand. Poly and acrylic don’t have aggressive solvents like nitro does, so need to be sprayed either on a slightly wet surface to bond with the layer below, or on to a dry surface that’s had a light fine sand to give it something to grab on to. If you wait and sand, then you’ll need more layers of clear. But you normally only want to apply a maximum of three layers a day, so I’d suggest three coats within the manufacturer’s re-coat period, then wait a day, a light sand (just to give a surface to key to) and then three more coats.
I wouldn’t worry about runs until the final sand. Being thick they take a couple of days to dry enough to sand back. You don’t want to sand a run shortly after spraying as it will be wet inside and is likely to leave a hollow as a result (though that may just be nitro). But even so, it’s easier to sand dry clear coat!
Dust and insects are another matter. Any significant dust or insect attachment needs to be removed before the next coat goes on. But the more you sand to remove these items, the more layers you’ll want to apply.
Final sanding and polishing can be a 2-stage process. I like to leave the clear coat to dry for a few days, and then give it an initial sand with P600 to a flat surface; no dips, bumps or ‘orange peel’. If I have any runs to remove, then I will use P240 just on the run areas first. This will give the finish a much greater surface area, which should allow any remaining solvent to escape more easily.
The longer you wait before the final sanding and polishing stages, the harder the finish will be and the better the shine (a 2K finish is the exception where I believe you should be able to do it after a day - though I’ve never used it so this may be incorrect).
I almost always wet sand. I’ve tried dry sanding and will sometimes dry sand a small area like a headstock. But you will get balls of finish clogging the paper and these can scratch the finish if you don’t remove them or keep changing paper.
If you wet sand, you will need to make sure that the edges of any post, pot, switch or jack holes are sealed with either sufficient finish or wax, otherwise the water will get in, expand the wood and the finish around the holes can crack.
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