You definitely want to exhaust outside your shop. I have filters on my exhaust to catch the big stuff before the fans, but a lot still gets on the fans and goes out the window I use for exhaust. So, my booth is negative pressure, but that is less than ideal as it pulls in dust through every opening in the booth and whenever you open the door with the fans on. I sometimes wish I had added fans on the intake side to provide positive pressure in the booth to help with dust control.

That should be very effective. For anyone wanting a simpler and passive system, you can also just make a serpentine run of copper air lines and it will do the same without need for electricity. My shop is fairly large, 32x48 so I simply ran my 3/4” air lines near the 14’ high ceiling. My paint booth is at the opposite corner from my compressor. I ran a 3/4” loop around the perimeter of my shop and then ran 3/4” drops in 4 places where I needed air. I put a drain stub at each drop so I can drain water there, but I’ve yet to have any water at any drop. My compressor exits to a filter and water separator and regulator combination unit and I get a little moisture there, but very little. After the air climbs 12’ up to my copper loop, travels nearly 80’ to my paint booth drop and then down the 10’ long drop, the air is basically at ambient temperature and very dry. Obviously, if your compressor is right outside your paint booth, then you need a more advanced cooling system such as you built or you need a refrigerated drying unit or several vertical copper pipes in serpentine form.

I have not sprayed single stage metallic, but I am spraying a single stage 2K white aviation paint and Axalta recommends applying two medium wet cross coats to avoid tiger striping even with the plain old white paint. Cross coats are a pain on some shapes, but that might be worth trying on a test panel.

@Green machine Otranto What is the recoat window for your base? Two days is stretching it for many paints. Did you sand prior to clear? If you exceeded the recoat window and didn’t sand, that might also contribute to the orange peel, but I don’t think that would cause the bubbles. Those are probably from applying too thick a coat such that the surface skinned before the solvent from the clear was adequately released. It definitely is worth doing the calculation based on the coverage in the TDS. My Axalta paint says something like 600 square feet of coverage at 1 mil DFT. That is 600/128 =4.688 square feet per ounce. I think you said you sprayed 1.5 oz which would cover 7 square feet at my Axalta coverage. That would probably paint 3 guitar bodies. Then again, if your paint coverage is listed as 300 square feet per gallon, your application rate might be right on. Worth reading the TDS, doing the calculation and then spraying a test panel or two to check. I was spraying mine too heavy at first and got solvent pops and more orange peel than I like. Once I got my application rate better calibrated, my test panel finish looked much better. I used two 2x2’ test panels so I had exactly 8 square feet. I added a couple extra square feet to account for the overspray at the end of each pass and mixed paint for 10 square feet and that came out nearly spot on. Definitely worth the cost of a couple of sheets of aluminum in my case, but I would try to get test panels of similar material to what you are painting and practice on them to get things right before painting the actual item. Edit: Note that I masked off each coat so I could measure the DFT of the layers as applied. The left-most green stripe is the epoxy pretreatment required for aluminum. The gray stripe is the epoxy primer/sealer on top of the pretreatment. And the white is all three layers (1 coat pretreatment, 1 coat primer and two coats of single stage color) as they will be on the actual airplane.

@Green machine Otranto I’m guessing here, but the cold temps likely are slowing the solvent release speed dramatically. The skinning of the clear should also be slower at cold temps, but if the solvent release is slowed more than the skin time, that might be a contributing factor. I would also be a little concerned about your rapid application speed. If you are moving the gun fast, and especially if you have a slow fluid rate and are holding the tip more than 6” from the surface, the paint droplets may be skinning while in transit to the surface and not merging together well on the surface. This might be trapping air in the paint somewhat like putting a couple of layers of small marbles on a flat surface will have air pockets between the marbles. And if you are using high air pressure, that could make it even worse. I would think about trying the following: 1. Heat both paint and guitar body if possible before moving into the cool paint booth. 2. Use a little extra reducer. 3. Use the gun pressure the manufacturer recommends (my guns are 28 psi for my full size gun and 29 psi for my small spot repair gun if memory serves) 4. Hold the gun 6” or less from the surface. 5. Slow your speed so that the paint droplets meld together well and don’t appear dry at all upon application. 6. Experiment with overlap if the TDS doesn’t give a recommendation. My single stage paint suggests 50% overlap and speed so as to provide a medium wet coat. However, often clears will suggest much more overlap, up to 80% in some cases. This is where have a few test panels helps a lot as you can start the top of a panel with faster speed and more overlap and then slow your speed and lessen the overlap at the bottom of the test panel. That allows you to compare the results side by side and see if there is a sweet spot.

@Aaron Jokela I was pretty sure I knew what you meant as that has been my wet sanding experience also, but when I read the bullets my incongruity sensor went off.