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newSchoolWorks.com › VoTechWorks › Building & Construction › Drywall / Painting / Finishing › Spray Systems: Airless, HVLP, and Texture Application › Lesson 3
BLD-DRYW11-07 · Lesson 3 · 16 clock hours · lab

Airless Sprayer Setup, Calibration, and Flat-Surface Application

Objective. Students will set up an airless sprayer from a cold start—prime, select tip, set pressure, test pattern—and apply a waterborne coating to a primed drywall panel achieving a consistent wet film with 50-percent overlap, no runs, no holidays, and a dry film thickness within ±0.5 mil of the TDS target.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed professional engineer or master tradesperson or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

VoTechWorks program approval and accreditation are still in progress. Credentials are issued only by the certifying bodies named in each program, after their own exams.

Airless Sprayer Setup, Calibration, and Flat-Surface Application

How an Airless Sprayer Works

An airless sprayer uses a high-pressure pump—not compressed air—to force liquid coating through a small orifice in the spray tip. The sudden pressure drop atomizes the fluid into fine droplets. Because no air is mixed into the stream, overspray is reduced compared with conventional air spray, and production rates are high. Understanding the relationship between tip size, fluid pressure, and coating viscosity is the foundation of good airless spray work.

Tip Selection

Airless tips are identified by a three-digit number. The first digit, multiplied by 2, gives the fan width in inches at a standard distance. The last two digits give the orifice diameter in thousandths of an inch. A 515 tip produces a 10-inch fan and a 0.015-inch orifice; a 517 tip produces a 10-inch fan and a 0.017-inch orifice. For standard latex interior wall paint, tips in the 0.013–0.019 inch range are typical. Always check the coating's Technical Data Sheet (TDS) for the manufacturer's recommended tip size. Using too large an orifice wastes material and causes runs; too small an orifice causes tailing and excessive pressure demand.

Pressure: Minimum to Atomize

The cardinal rule of airless spray is use the lowest pressure that fully atomizes the coating. Start with the pressure control at its minimum, trigger the gun into a waste bucket, and raise pressure slowly until the fan pattern is uniform and the droplets are fine with no tails at the edges of the pattern. This is called the minimum-to-atomize point. Excess pressure increases overspray, accelerates tip wear, and raises the risk of injection injury. Document the pressure setting in your lab log so you can repeat it on the production panel.

Reading the Pattern

Spray a quick pass onto scrap and observe the fan:

Setup Sequence

1. Place the intake tube in a bucket of clean water or the appropriate solvent. Set the prime/spray valve to prime. Turn the unit on and run fluid until it flows cleanly from the prime port into a waste bucket. This flushes any storage fluid.

2. Place the intake tube in the strained, stirred coating. Continue priming until paint flows from the prime port, then switch the valve to spray.

3. Install the correct tip inside the tip guard. The tip guard is a mandatory safety device—never spray without it. It does not fully prevent injection injury but substantially reduces risk.

4. Set pressure to minimum. Trigger into a waste bucket until coating is flowing steadily.

5. Raise pressure to the minimum-to-atomize point. Spray a test pattern on scrap and evaluate before moving to the work surface.

Injection Injury Hazard — Critical Safety Warning

Airless sprayers develop pressures sufficient to inject fluid through skin, causing severe injury or tissue loss. The tip guard reduces but does not eliminate this risk. Never place any part of your body in front of the tip or orifice, even when the gun is not triggered. When clearing a tip blockage, always trigger the gun into a waste bucket and follow the manufacturer's reverse-tip procedure—never poke the orifice with a finger or tool while the system is pressurized. Before any service or tip change, relieve pressure completely: disengage the prime/spray valve, trigger the gun into a waste bucket, and verify the gauge reads zero. This is a lockout/tagout (LOTO) adjacent procedure—treat pressure as stored energy.

PPE Requirements

Wear safety glasses or goggles at all times. A properly fitted half-face respirator with organic vapor cartridges (or P100 particulate filters for waterborne coatings in enclosed spaces) is required—check the coating's Safety Data Sheet (SDS) for the correct cartridge type. Nitrile gloves protect skin from prolonged coating contact. Hearing protection is advisable if compressors or other loud equipment operate nearby.

Application Technique for Flat Surfaces

Measuring Wet and Dry Film Thickness

A wet-film (WFT) gauge is a notched comb gauge. Press it perpendicular into the fresh wet film immediately after application and read the last notch that is coated. Compare the WFT reading to the TDS conversion: WFT = DFT ÷ (volume solids %). If the TDS specifies a dry film of 1.5 mils and the paint has 40% volume solids, the required WFT is 1.5 ÷ 0.40 = 3.75 mils. Measure WFT after the first coat, before it flashes, so you can adjust technique on the second coat if needed.

After full cure, a dry-film thickness (DFT) gauge gives the final measurement. Magnetic gauges are used on steel substrates; non-contact eddy-current gauges work on non-ferrous and non-metallic substrates. For drywall panels in this lab, follow the instructor's direction on gauge type and zeroing procedure. Take readings at five evenly spaced points and compare each to the TDS target. All five must fall within ±0.5 mil to pass.

Cleanup

Relieve system pressure before any cleanup step. Flush the system with the appropriate solvent (water for waterborne latex) until the fluid runs clear. Remove and clean the tip separately. Dispose of rinse water containing paint solids according to local regulations—do not pour down a floor drain without authorization.

Key terms10

Tip orifice sizeThe diameter of the spray tip opening, expressed in thousandths of an inch (e.g., 0.015 inch for a 515 tip); determines flow rate and is matched to coating viscosity and TDS recommendations.
Fan widthThe width of the spray pattern produced by an airless tip at a standard distance, calculated by multiplying the first digit of the tip number by 2 (e.g., a 515 tip produces a 10-inch fan).
Minimum to atomizeThe lowest fluid pressure at which an airless sprayer fully breaks the coating into fine, uniform droplets without tailing or coarse texture; the correct operating pressure setting.
TailingA spray defect showing heavy, unatomized streaks at the edges of the fan pattern, caused by pressure that is too low or a tip orifice that is too large for the fluid viscosity.
50-percent overlapAn application technique in which each spray pass covers half of the previous pass, ensuring a uniform total film thickness across the surface.
Wet-film thickness (WFT) gaugeA notched comb tool pressed into freshly applied wet coating to measure film thickness in mils; used to verify adequate film build before the coating flashes or dries.
Dry-film thickness (DFT)The thickness of a coating layer after full solvent evaporation and cure, measured in mils; must meet the manufacturer's TDS specification for proper performance.
Technical Data Sheet (TDS)A manufacturer document specifying application conditions, recommended tip size, spread rate, wet and dry film thickness targets, recoat times, and other performance data for a specific coating product.
Tip guardA safety shroud installed around the airless spray tip that reduces—but does not eliminate—the risk of high-pressure injection injury by deflecting the spray stream away from the operator's body.
HolidayA skipped or uncoated area in a paint film; a defect where the substrate is visible through an area that should be fully coated.

Worked examples4

1. The TDS for a latex wall paint states a target dry film thickness (DFT) of 1.5 mils and lists the volume solids at 40%. What wet film thickness (WFT) must you achieve to hit the DFT target?
  1. Recall the formula: WFT = DFT ÷ Volume Solids (expressed as a decimal).
  2. Convert volume solids to a decimal: 40% = 0.40.
  3. Divide: WFT = 1.5 mils ÷ 0.40 = 3.75 mils.
  4. Set this as the target when you press the WFT comb gauge into the fresh wet coat—the notch at 3.75 mils (or the nearest calibrated notch at or just above it) should be wetted.
Answer: Required WFT = 3.75 mils.
2. You are using a 517 tip (17-thousandths orifice, 10-inch fan). After applying one coat, your DFT readings at five points are: 1.2, 1.8, 1.4, 1.9, and 1.3 mils. The TDS target is 1.5 mils. Which readings are outside the ±0.5 mil tolerance, and what is the range of the data set?
  1. Determine the acceptable range: 1.5 − 0.5 = 1.0 mil (low limit); 1.5 + 0.5 = 2.0 mils (high limit).
  2. Check each reading against the limits: 1.2 mil — within range (1.0–2.0); 1.8 mil — within range; 1.4 mil — within range; 1.9 mil — within range; 1.3 mil — within range.
  3. All five readings fall between 1.0 and 2.0 mils, so none are outside the ±0.5 mil tolerance.
  4. Calculate the range: highest reading − lowest reading = 1.9 − 1.2 = 0.7 mil. This tells you film thickness varied by 0.7 mil across the panel, which is acceptable but suggests slight inconsistency in gun speed or overlap that can be refined.
Answer: All five readings pass the ±0.5 mil tolerance. The data range is 0.7 mil (1.2 to 1.9 mils).
3. Your spray tip has a fan number of 5 (first digit), making the fan width 10 inches. You need to set up 50-percent overlap passes. How far should the leading edge of each new pass be from the leading edge of the previous pass?
  1. Determine the fan width: first digit × 2 = 5 × 2 = 10 inches.
  2. Calculate 50-percent overlap: 10 inches × 0.50 = 5 inches.
  3. This means each new pass starts 5 inches from the start of the previous pass, covering the inner 5 inches of that pass while adding 5 inches of new coverage.
  4. Practical check: if you marked the panel in 5-inch horizontal bands, each trigger pull should shift the gun center by 5 inches from the previous pass center.
Answer: Each pass center should be offset 5 inches from the previous pass center to achieve 50-percent overlap with a 10-inch fan.
4. A student holds the gun at 18 inches from the surface instead of the specified 12 inches. Without changing pressure or tip, how does this affect the fan width and the effective film thickness per pass, and what defect is likely?
  1. As distance increases beyond the rated standard distance, the fan pattern expands and the droplets travel farther before hitting the surface.
  2. A wider fan at the same flow rate means the coating is spread over a larger area, reducing the wet film thickness deposited per pass.
  3. The longer travel time also allows more solvent to evaporate before the droplets land, producing 'dry spray'—a rough, sandpaper-like texture caused by partially dried droplets that do not flow out.
  4. Conclusion: holding the gun 6 inches too far will likely produce insufficient film build, dry spray texture, and possible holidays—all defects that require re-spraying.
Answer: Increased gun distance thins the film below target and causes dry spray. Keep the gun at 12 inches as specified.

The math in this lesson2

Learners check five DFT readings against a percent tolerance and set 50-percent pass overlap.
7.RP.3A-CED.4
Brush up in the math halls at newSchoolWorks.com:
In class: Setup drill: each student follows a printed setup checklist (flush, prime, tip guard installation, pressure set at minimum to atomize) and documents each step with checkpoint initials; instructor signs off before student points gun at the panel. · Test-panel sequence: student sprays a 2 × 4-foot primed drywall panel at three pressure settings (low, correct, high), photographs each, and annotates the photos to identify atomization defects (tailing, orange peel, overspray) in a lab-log entry. · Full-panel production pass: student applies two coats of latex wall paint at the correct pressure and tip, maintaining a 12-inch gun-to-surface distance and 50-percent overlap; wet film is measured with a wet-film gauge after the first coat before it flashes.
Materials: Airless sprayer (1/4 HP minimum electric, with 515 and 517 reversible tips), tip guards, wet-film thickness gauge, dry-film thickness gauge, 2 × 4-foot primed drywall panels (minimum two per student), latex interior paint, stirring sticks, strainer buckets, drop cloths, painter's tape, lab-log notebook, camera or smartphone
Check: Instructor measures dry film thickness at five points on the finished panel using a dry-film gauge; all readings must be within ±0.5 mil of the TDS target. Instructor visually inspects for runs, sags, holidays, and dry spray; any defect requires student to identify cause and re-spray a fresh panel. Pass requires both thickness tolerance and defect-free surface.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

OSHA 10 – Tool and Equipment Safety / NCCER Painting – Spray Equipment
1. What is the primary reason to use the minimum pressure that fully atomizes the coating when operating an airless sprayer?
NCCER Painting – Spray Equipment Operation
2. A spray tip is labeled 515. What fan width does this tip produce at standard distance?
NCCER Painting – Spray Defect Identification
3. A student notices heavy streaks at both edges of the spray fan but a clear, well-atomized center. This defect is called:
OSHA 10 – Lockout/Tagout / Stored Energy
4. Before removing the spray tip to clear a blockage on a pressurized airless sprayer, what is the correct first action?
NCCER Painting – Film Thickness Measurement
5. A latex interior paint has a TDS target DFT of 2.0 mils and volume solids of 50%. What WFT is required to achieve the target DFT?
OSHA 10 – Personal Protective Equipment
6. Which PPE is required when spraying waterborne latex paint in an enclosed space with an airless sprayer?
NCCER Painting – Application Technique
7. A student applies paint with a 10-inch fan tip and overlaps each pass by 50 percent. A second student uses the same tip but overlaps only 25 percent. What defect is most likely on the second student's panel?
NCCER Painting – Quality Control / Film Thickness
8. Five dry-film thickness readings on a finished panel are 1.1, 1.3, 1.6, 1.4, and 2.2 mils. The TDS target is 1.5 mils with a ±0.5 mil tolerance. How many readings fall outside the acceptable range?
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