Many finishers use airless pumps and spray guns even though they don’t produce the highest quality results. Conventional compressed air, HVLP turbine and compressed air, and air-assisted airless are all capable of producing noticeably less orange peel if adjusted properly.
But airless sprayers are very popular with painters because of the much larger area that can be covered in less time. And many of these painters also do finishing with non-pigmented coatings. So it’s only natural to continue using these systems when spraying cabinets and furniture.
Here are some tips for getting the best possible results:
Set the proper pressure
Proper pump pressures for getting the best results vary with the viscosity of the coating being used and the temperature. All coatings, whether clear finish or paint, become more viscous, or thicker, in cooler temperatures.
It’s easy to solve any potential problem by simply turning up the pump pressure to the maximum and spray. This will work, but there will be increased waste because of bounce-back and more dry spray because of the droplets drying out. The dry spray won’t bond well and some of it might bounce off and settle back on the surface, causing it to feel rough.
Instead, find the pressure that eliminates the “tails” in the spray pattern with the least amount of pressure. Tails are the thicker lines of paint or finish at the edges of the spray pattern and slightly separated from the rest of the pattern.
As you turn up the pump pressure, these tails disappear and the spray pattern becomes even. At the point the tails disappear, stop turning up the pressure.
Keep in mind the effect of temperature on the viscosity of the coating at different times of the day so you can make the proper adjustments.
Replace worn spray tips
The spray tip is the orifice, or hole, the coating is pushed through by the pump. This hole is not round as it is with air-supplied spray guns. It is squeezed to create an elongated opening or two little “wings” of metal that are used to squeeze the pattern.
As paint or finish is pushed through this opening at very high pressure, friction wears the metal, changing the spray pattern from elongated towards circular. More of the coating is deposited in the center of the pattern than at the edges making it increasingly impossible to keep the thickness even.
The natural tendency is to turn up the pressure, but this just makes the problem worse because of bounce-back, waste and increased wear to the tip. Instead, replace the tip.
One way to determine if the tip is worn is to spray a short horizontal burst on vertical scrap wood or cardboard and look at the runs. If they are fairly even across the pattern, the tip is good. If the runs are much longer in the middle than at the edges, the tip is worn.
Another way to keep up with the wear to a tip is to create a control by spraying a burst using a new tip, then periodically compare the pattern of the tip you’re using with the control pattern. When the elongated pattern of the tip you’re using shrinks by several inches, replace it.
Use a proper size tip
Tips vary in size. The larger the elongated orifice, the more coating can be deposited and the more pressure is needed to atomize it well. Or, thought of another way, the smaller the elongated tip, the less pressure it will take to atomize a liquid, but the more difficult it will be to atomize thicker and more viscous coatings well.
So you would choose a smaller tip for a clear lacquer or varnish and a larger tip for latex paint. You can also choose tips for wider and narrower spray patterns.
Tips are usually labeled with a three-digit number such as 309 or 517. These could also be the last three digits of a model number. The first digit is one-half the fan width in inches with the spray gun held 12 inches from the surface. The last two digits tell you the size of the orifice in thousandths of an inch.
So a 309 tip would spray a six-inch-wide pattern through a .009-inch orifice. A 517 tip would spray a 10-inch-wide pattern through a .017-inch orifice.
As a guide, for spraying clear finishes, 409 to 511 tips work well. For spraying latex paint, 517 to 619 tips work well. But a lot depends on the object you’re spraying. Most important to consider is whether the surfaces being sprayed are narrow or wide. For narrow surfaces, you would choose a tip with a small first number. For wide surfaces, such as tabletops or the sides of a building, you’d choose a larger first-number tip.
Use fine-finish tips
To reduce orange peel, check if your brand of airless offers a fine-finish tip. This type of tip has two orifices. The first pre-atomizes the coating so the second can create a smaller particle size.
Another advantage of fine-finish tips is that good atomization and a good spray pattern can be achieved with less pump pressure.
Keep the filters clean
There are typically three filters the coating passes through. It’s important to keep these filters clean to prevent clogging, prevent damage to the piston and, of course, to get the most debris-free results.
The first filter the coating passes through is at the inlet to the siphon hose. This filter is sometimes referred to as the “rock catcher” because it catches large debris that could damage the piston.
The second filter is in the sprayer’s manifold and catches globs of paint or finish before they reach the spray gun.
The third filter is in the spray gun. These three filters use increasingly finer mesh to catch increasingly finer debris.
Check these filters often to be sure they’re clean. Keeping them clean will reduce the pressure you’ll need to get good results.
Always use a tip guard when spraying.
Always engage the trigger lock on the spray gun when it isn’t in use.
Don’t make adjustments to the spray gun or pump without first shutting off the pump and releasing the pressure.
Be sure that hoses and all fittings meet the pressure requirements for use with the pump pressures you’re using.
Bob Flexner is author of “Understanding Wood Finishing” and “Flexner on Finishing.”
This article originally appeared in the March 2015 issue.