The Essential Balancing Act – Atomization

What is atomization and what does it do? Atomization is the breaking down of the fluid stream, using pressurized air, into fine droplets which are then projected onto the target surface.

Selecting the right air cap set

It all begins with mounting the correct air cap set (consists of a fluid nozzle, needle and air cap) for the finish you’re planning to use.

Simply stated, the higher the viscosity (think thicker!) the larger the nozzle needed to pass that finish through the hole.

And because that fluid stream will be larger, your air cap also needs to be larger to deliver more air to break up that larger, heavier fluid stream. You could refer to a chart, but realistically speaking, for most applications you require only one of three sets: 1.0 for dye or shellac; 1.3 for sanding sealer or topcoats (lacquer, varnish or polyurethane); and 1.8 for anything of higher viscosity (again, think thicker) such as tinted lacquer or latex paint.  And if you have an unpressurized gravity gun, move up to the next larger set for all finishes.

Setting up your spray gun

With the optimal air cap set mounted and your gun squeaky clean and properly lubricated, strain the finish as you load your gun (or pressure pot). Don’t overfull the reservoir; about ¾ is right.  Oh, yeah, and don’t forget to put on your protective mask and goggles. Safety!

Let’s start by setting your gun to full air, widest possible fan and the fluid control knob opened 2 full turns from the full off position.  Orient your air cap to deliver a vertical fan pattern (air cap horns horizontal).  Note that the manual that came with your system will indicate where those various controls are located and how to adjust them.  Then set up a board (I use cardboard box scraps cut to 2’ squares, which I fasten to the wall of my booth) for test spraying, which will allow you to see how things are proceeding as you adjust your gun.

Holding your gun 7” (the standard distance for spraying) from the test board and ensuring it is perpendicular to the surface both horizontally and vertically, squeeze the trigger for a brief second or two. Don’t move the gun along as you normally would when spraying; aim it at the same place. Then take a critical look at your test board results.

First, you’re looking for any evidence of blockage in the air passages (the air diffuser, air passages inside the gun or the air cap itself). The pattern should be oval shaped. If it is comma or curved shaped, there is a blockage:  one of your air cap horns, or the air diffuser or air passages need to be cleaned. If it’s clean and there’s still a misshaped pattern, it may be that your needle or perhaps the nozzle has been damaged.  Address the issue then conduct test sprays to confirm that it’s been corrected.

Looking again at your pattern, if it is hourglass shaped, it most likely means that your air volume is too high and needs to be reduced. Make small incremental changes – nothing greater than 1/8 of a turn. Conversely, if the pattern is too heavy in the center, increase the air pressure, or, if you’re already full open, it means your finish’s viscosity is too high (again, think thick!) for the air cap set and needs to be thinned or the next larger air cap set installed. Continue performing test sprays and air volume adjustments until you achieve the desired pattern.

Now we’re (finally, you say?) at the point where we can see if the finish is being correctly atomized. What we’re looking for are very minute droplets hitting the test panel. These droplets will often be more visible towards the outer area of the oval pattern you sprayed.  If the droplets are large or coarse, it means the ratio of fluid to air is too high: turn down the fluid knob 1/8 turn and perform another test spray. If they appear just about right, go the other way to see if it can be improved.  Keep doing this until you are satisfied that the atomization is as fine as possible.  Be willing to play around with the air volume as well, and only make small adjustments (1/8 turn) between each spray test.  And don’t try more than one setting at a time; either fluid or air, but not both… at least not until you’re confident you’ve got this in the bag.


With these steps completed, your gun is now properly set to deliver a finely atomized spray, at the widest possible fan pattern – as that’s the pattern you’ll be using on most of your projects.  But if what you’re spraying calls for a narrower fan or a circular pattern, or if you need to reduce the air pressure to work on the inside of a cabinet, you’ll have to make some changes.  Adjust the fan width or air pressure (or both, in some cases), then go back and perform the atomization checks.  In no time at all, these checks and adjustments will become second nature, allowing you to efficiently move from one pattern setting to another throughout the spraying session.

Give yourself a pat on the back, as you’re now well on your way to delivering great finishes!

Woodworking expert Marty Schlosser has been designing, making and finishing furniture for nearly 50 years. Before retiring, Marty served as the president of the Ottawa Woodworkers Association, to which he received their prestigious Danny Proulx Memorial Award. He is also a founding member of Kingston Wood Artisans, the local woodworking club in Kingston, Canada. When you don't see Marty sharing his woodworking knowledge through neatly written articles, you may find him conducting Fuji Spray's annual spray finishing workshops in Toronto, Canada - where people all over North America wait for, every year.

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