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newSchoolWorks.com › VoTechWorks › Building & Construction › Drywall / Painting / Finishing › Drywall Texture: Application Techniques and Finishing › Lesson 3
BLD-DRYW11-04 · Lesson 3 · 16 clock hours · practice

Spray Texture: Hopper Gun Operations—Orange Peel and Knockdown

Objective. Students will set up, operate, and adjust a hopper gun and compressor to spray orange peel and knockdown textures on ceiling and wall panels to a specified bead size and coverage density, then safely clean and store all equipment.

⚠ 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.

Spray Texture: Hopper Gun Operations—Orange Peel and Knockdown

Spray texture gives walls and ceilings a consistent decorative surface faster than hand-rolled or hand-applied methods. Two of the most common spray textures are orange peel and knockdown. Both use the same basic equipment—a hopper gun and an air compressor—but differ in bead size, air pressure, and whether a trowel is applied after spraying.

How a Hopper Gun System Works

A hopper gun is a pneumatic sprayer with a large cup or hopper that holds pre-mixed texture compound. Compressed air passes through the gun body and draws material out of the hopper, atomizing it into droplets that land on the surface as beads. Key components are:

Texture Compound Preparation

Pre-mixed texture compound must be thinned to a consistency appropriate for spray application—typically described as a thin milkshake or heavy cream. Over-thick compound clogs the orifice and produces a splattery, uneven pattern. Over-thin compound runs and sags. Mix and test a small batch first, then adjust with clean water in small increments. Record the water-to-compound ratio in your lab log so you can reproduce results.

Orange Peel Texture

Orange peel texture mimics the surface of—as the name suggests—orange skin: small, tight, rounded beads with shallow relief. To achieve it:

1. Use a smaller orifice tip (refer to the manufacturer's chart for the specific tip size).

2. Set air pressure at the higher end of the recommended range for that tip and compound viscosity.

3. Hold the gun farther from the surface (typically 18–24 inches, but follow your reference sample) and keep a steady, consistent speed across the panel.

4. The goal is uniform, small beads. No troweling is applied—the surface dries as sprayed.

Adjust pressure and gun speed together. If beads are too large, increase pressure slightly or move the gun faster. If coverage is too light, slow the gun or open the material valve slightly. Make one adjustment at a time and document each change.

Knockdown Texture

Knocdown texture starts the same way—spray a field of medium-to-large beads—then a trowel is lightly skimmed across the wet beads to flatten their peaks before drying. This creates irregular, flattened islands separated by recessed areas.

1. Use a larger orifice tip and set air pressure at the lower end of the recommended range to produce larger, wetter beads.

2. Hold the gun closer to the surface (approximately 12–18 inches) to land heavier droplets.

3. After the entire panel is sprayed, wait for the beads to partially flash off—they should lose their shine but still be wet enough to compress. This timing window varies with temperature and humidity and is critical. Too soon and the trowel drags the compound off; too late and it tears rather than flattens.

4. Using a clean 12-inch knockdown trowel held at a very low angle (nearly flat), make one light pass across the surface. Do not press hard or re-stroke the same area.

PPE and Safety Requirements

Spray texture operations create airborne compound mist and elevated noise levels. Wear the following at all times during spraying:

Before connecting air lines, confirm the compressor is off and the regulator is set to zero. Never exceed the maximum rated pressure of the hose, gun, or fittings. Inspect all connections for leaks by feel and sound after pressurizing—a leak at a fitting can be corrected by tightening; a cracked hose must be replaced before use.

Equipment Cleaning and Storage

Texture compound is water-based and must be cleaned up before it hardens. After spraying:

1. Empty and wipe out the hopper.

2. Pour clean water into the hopper and spray until water runs clear from the nozzle.

3. Disassemble the nozzle and orifice tip and rinse individually.

4. Inspect the orifice opening for wear or buildup. A damaged orifice gives an inconsistent pattern and must be flagged for replacement.

5. Reassemble the gun, wipe exterior surfaces, and complete the post-use equipment condition form before returning equipment to storage.

Never leave compound in the gun overnight—hardened material inside the orifice or passages can permanently damage the gun.

Key terms9

Hopper gunA pneumatic spray tool with a large material cup (hopper) that uses compressed air to atomize and project texture compound onto a surface.
Orifice tipThe interchangeable nozzle opening that controls droplet size; a smaller orifice produces finer beads and a larger orifice produces coarser beads.
RegulatorA device installed on the compressor or air line that controls and displays the delivery pressure reaching the spray gun, measured in PSI.
Orange peel textureA spray-applied wall or ceiling finish characterized by small, tight, rounded beads resembling the skin of an orange; applied at higher pressure with a smaller orifice tip and left unsanded.
Knockdown textureA spray-applied finish in which larger wet beads are partially flattened with a low-angle trowel pass before drying, creating irregular, flat islands with recessed areas between them.
Flash-offThe partial drying of sprayed compound in which surface moisture evaporates until the beads lose their sheen but remain workable; the correct point to begin troweling knockdown texture.
Material valveThe control on a hopper gun—trigger or knob—that regulates how much compound enters the airstream; opening it increases bead size and coverage.
P100 respiratorA half-face air-purifying respirator fitted with P100 particulate filter cartridges, rated to filter at least 99.97% of airborne particles; required when spraying texture compound.
CFM (cubic feet per minute)The unit measuring the volume of air a compressor delivers; the hopper gun requires a minimum CFM to maintain consistent spray pattern at the desired pressure.

Worked examples4

1. The manufacturer's chart recommends a starting pressure of 30 PSI for orange peel texture with the small orifice tip. After the first test pass, the beads are too large. You decide to increase pressure in 5 PSI increments. What are the next two pressure settings you will try, and what is the total increase after both adjustments?
  1. Starting pressure: 30 PSI.
  2. First increment: 30 + 5 = 35 PSI.
  3. Second increment: 35 + 5 = 40 PSI.
  4. Total increase from starting pressure: 40 − 30 = 10 PSI.
Answer: Next settings are 35 PSI, then 40 PSI. Total increase after both adjustments is 10 PSI.
2. You are spraying a 4 × 8 ft ceiling panel (32 square feet) for knockdown texture. Your lab log shows you used one full 5-gallon bucket of thinned compound to cover three identical panels. Approximately how many square feet does one 5-gallon bucket cover, and how many square feet are covered per gallon?
  1. Total area covered by one bucket: 3 panels × 32 sq ft per panel = 96 sq ft.
  2. Coverage per gallon: 1 bucket = 5 gallons, so coverage per gallon = 96 ÷ 5 = 19.2 sq ft per gallon.
Answer: One 5-gallon bucket covers 96 square feet; coverage is approximately 19.2 square feet per gallon.
3. You spray a knockdown panel and notice the compound took 4 minutes to flash off under current shop conditions (72°F, moderate humidity). On the next panel you want to start your trowel pass at exactly the flash-off window. The clock shows 9:14 AM when you finish spraying the second panel. At what time should you begin troweling?
  1. Flash-off time under these conditions: 4 minutes.
  2. Spray finish time: 9:14 AM.
  3. Add 4 minutes: 9:14 + 0:04 = 9:18 AM.
Answer: Begin the trowel pass at approximately 9:18 AM.
4. Your compressor gauge reads 60 PSI in the tank. The regulator is set to deliver 25 PSI to the gun. After spraying for several minutes, the tank pressure drops to 40 PSI but the regulator still holds 25 PSI at the gun. By how many PSI did the tank pressure drop, and is the regulated pressure at the gun affected?
  1. Tank pressure drop: 60 − 40 = 20 PSI drop in tank.
  2. Regulated pressure at the gun: The regulator is designed to maintain its set output (25 PSI) as long as tank pressure remains above the set output pressure.
  3. Since 40 PSI (tank) is still greater than 25 PSI (set output), the regulator can hold 25 PSI at the gun.
  4. Therefore, the gun pressure is not affected by this tank pressure drop.
Answer: The tank pressure dropped 20 PSI (from 60 to 40 PSI). The regulated pressure at the gun remains at 25 PSI because tank pressure is still above the regulator set point.

The math in this lesson1

Learners compute square feet covered per bucket of thinned compound from three sprayed 32 sq ft panels.
6.RP.3
In class: Set up a compressor and hopper gun system: connect air lines, check for leaks, adjust regulator to the manufacturer-recommended starting pressure, load mixed texture compound, and complete a pre-operation checklist before any spraying begins; instructor verifies setup and initials the checklist. · Spray two ceiling panels in sequence—first for orange peel (smaller bead, higher pressure) and then for knockdown (larger bead, lower pressure with timed knockdown using a trowel)—adjusting air pressure and material-valve settings in documented increments until the pattern matches reference samples; record all settings in the lab log. · After spraying, fully clean the hopper gun with clean water following the manufacturer's flushing procedure, disassemble the nozzle and orifice, inspect for wear, reassemble, and complete a post-use equipment condition form noting any items needing maintenance.
Materials: Electric or gas-powered hopper gun with interchangeable orifice tips, air compressor with regulator and gauge, air hose, pre-mixed texture compound, clean water, 5-gallon buckets, 12-inch knockdown trowel, primed 4×8 drywall panels on ceiling jacks and wall stands, drop cloths, P100 half-face respirator, safety glasses, nitrile gloves, hearing protection, manufacturer operation manual, pre-operation and post-use checklists, NCCER Drywall spray texture reference photos
Check: Instructor conducts a live observation using a skills checklist covering safety setup, pressure adjustment, spray pattern consistency, and equipment cleaning; students must complete all checklist items correctly—any critical safety step omitted results in an immediate stop and remediation before re-attempt.

Practice check8

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

NCCER Drywall – Safe Equipment Operation
1. When setting up a hopper gun and compressor before spraying, what is the correct order for the first two steps?
NCCER Drywall – Spray Texture Techniques
2. To achieve an orange peel texture, which combination of orifice tip size and air pressure is correct?
NCCER Drywall – Spray Texture Techniques
3. During knockdown texture application, what is 'flash-off' and why is it important?
OSHA 10 – Personal Protective Equipment
4. Which PPE item is required specifically to protect against airborne compound mist during hopper gun spraying?
NCCER Drywall – Spray Texture Techniques
5. A student sprays a test panel and finds the beads are too large and wet for orange peel texture. Which single adjustment is most likely to correct the pattern?
NCCER Drywall – Tool and Equipment Care
6. After finishing a spraying session, what is the correct first step in cleaning the hopper gun?
OSHA 10 – Hazard Recognition and Safe Work Practices
7. While spraying, a student notices a hissing sound and feels air escaping from an air hose fitting. What is the correct immediate action?
OSHA 10 – Personal Protective Equipment
8. Why is hearing protection required when operating a hopper gun and compressor, even for a single lab session?
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