From what I can find, information on spraying shellac is somewhat scant.
I'll try to sum up the information I've found, and hopefully it gives you something good, or at least a good starting point to begin your own experimentation.
From songbirdhd.blogspot.com, the major points are:
- Use a one-pound cut (one pound of shellac flakes in one gallon of alcohol), which can be sprayed through any spray gun that will spray lacquer
- Filter the dissolved mixture to remove the undissolved solids/leftover crud
- Spray thin, even coats
- Consider sealing the grain first with an oil-based polyurethane finish to keep the grain from being raised (alcohol is a polar solvent, like water, and will raise the grain in some woods)
- Spray 2 light coats, sand with 320-400 grit, spray another 2 light coats, buff with 0000 steel wool (if needed)
This forum thread on WoodWeb has the following advice:
- Spraying, considering the lightness of the coats needed for a drip-free finish, takes much longer than brushing
- If you're to level the finish (i.e., sand flat after the finish has hardened), brushing is generally faster
- Premixed shellac sprays have a shelf life - avoid any with a manufactured date over 1 year, or mix your own from flakes
- A shellac finish is much easier to repair than other finishes (rub out, reapply a thin coat, sand flat, polish)
Saw Mill Creek user Todd Burch has this to say:
I've sprayed a lot of shellac. Sealcoat, for my taste, is ready to shoot right out of the can. I'm not familiar with that HF gun. Get some cardboard, or scrap plywood, or a roll of butcher paper you can rip off and toss in the trash and practice in a vertical mode until you get comfortable with the flow and pattern. Horizontal is easy - a thick wet finish resting flat won't run as easily. Shellac will run quick, so dryer coats are better than wetter coats.
My approach to spraying shellac is this... you are going to be rubbing it out anyway, so why waste time trying to get a perfect finish by spraying the perfect coat? Just get it on there and build it up. Do 4 or 5 coats in a day. After the first coat dries for about an hour, sand with 220 FRE CUT paper, then get the other coats on there. Let it dry overnight and the next day 220 or 320 it again. No muss, no fuss.
With a gravity gun, you are limited in the positioning and angle of the gun more so than with the other styles of guns. If you will be shooting inside a cabinet or box, or at weird angles, plan your route ahead of time and maybe rearrange your project mid way through so that you can achieve consistent coverage.
Being new to spraying, there are a few things you should read up on:
There are measuring devices that tell you the viscosity of fluids. There are several types: Ford cups are one style, and there are others (can't remember...). Basically how they work is you fill them up with what you will be spraying and time how long it takes for them to drip out the little hole in the bottom of the cup. (Measurements like "4 seconds in a #2 cup", or some such specification. I don't know that Sealcoat specifies this on the can, but maybe you could find it on the Zinsser web site.
Also there are fluid and pressure adjustments on your gun (I'm assuming). You'll want to find the right mix to give you a good pattern. There is a technique to holding the gun too (distance from the work, speed at which you move, angle of the gun, how you overlap passes, how you shoot off the edge, etc., etc.).
There is also a thing called a "wet mil gauge". This is a business-card shaped piece of metal, (maybe plastic), kinda-sorta notched like a trowel around the edges, but the notches are different sizes and stepped for height. How it works is that you spray a section of wood, and while it is wet, you place the edge of the gauge in the wet finish and remove it. Depending on what footprints it leaves in your finish, you can tell how many mils thick your wet coat is. Again, most quality finishes will give you a specification for how thick you should be spraying, i.e., 4 to 5 wet mils per coat, two coats, or whatever. There is also a dry gauge too, but I haven't used one of those.
Both the viscosity cups and the wet mil gauge are tools I don't use every time I spray. But, when you or I are learning, or spraying a finish that we haven't sprayed before, or are in doubt, or we're having issues, they are excellent aids to confirm what we might otherwise be guessing at.
A quick google search for "spraying shellac" will turn up many other results, but I've tried to summarize what I think is some pertinent information above.
As far as how to mount your pieces in your spray booth, the best advice I can give you is to mount it such that you can easily access the areas you are trying to spray. It all depends on what exactly you're trying to finish. For example, doors may be hung from the ceiling to access virtually the entire panel at once like so: