Why Is My Spray Pattern Uneven? Common Causes Explained

An even spray pattern is essential for consistent coverage and a high-quality finish. If the spray fan becomes patchy, distorted or heavier on one side, it can lead to overspray, poor film thickness, wasted coating and costly rework.

Fortunately, an uneven spray pattern is often caused by a simple issue, such as a blocked tip, incorrect pressure or inconsistent technique. A methodical check can help operators identify the cause quickly.

Although the exact shape depends on the equipment and application, a good spray pattern should have:

• An even, symmetrical shape
• Consistent material distribution
• Soft edges
• Stable atomisation
• No gaps, heavy lines or pulsing

Always carry out a test spray on a suitable surface before coating the workpiece. This allows the pattern to be checked without affecting the finished component.

A poor spray pattern can cause:

• Inconsistent coverage and film thickness
• Runs, sags or patchy areas
• Excessive overspray
• Increased material use
• Longer production times
• Additional inspection and rework
• Reduced coating performance

Applying more coating or immediately increasing the pressure may hide the problem temporarily, but it can also increase waste. It is better to identify and correct the underlying cause.

1. A blocked spray tip

Dried coating, debris or contamination can partially block the spray tip and disturb material flow. The fan may become narrow, irregular or heavier on one side.

Follow the manufacturer’s pressure-relief procedure before inspecting the equipment. Clean the tip using the recommended method and a suitable cleaning product. Avoid inserting metal objects into the opening, as this may damage the tip.

Regular cleaning and correctly straining the coating can help prevent further blockages. Blocked tips are identified as a common cause of poor spray patterns.

 

2. A worn or damaged tip

Spray tips gradually wear as coating passes through them under pressure. As the opening becomes larger, the fan may widen and lose definition, increasing material flow and overspray.

If cleaning does not restore the pattern, inspect the tip for wear or damage and replace it when required. Any replacement must be suitable for the coating, equipment and required fan width.

 

3. Incorrect pressure

Low pressure can prevent the coating from atomising properly, producing an incomplete fan or heavy lines at the edges, often called tails.

Increase the pressure gradually until the fan is fully developed. However, avoid using more pressure than necessary. Excessive pressure can increase overspray, coating consumption and component wear.

The aim is to use the lowest pressure that produces a stable and consistent pattern.

 

4. The wrong tip size

A tip that is too small may restrict a thick coating. A tip that is too large can deliver excessive material or exceed the pump’s capacity, causing pressure and pattern problems.

Check the coating technical data sheet and equipment manufacturer’s guidance before selecting a tip. Consider:

• Coating viscosity
• Required flow rate
• Fan width
• Pump capacity
• The size and shape of the workpiece

Tip selection, material viscosity and equipment capacity are important factors which affect spray patterns.

 

5. Restricted fluid delivery

A stable spray pattern depends on a consistent coating supply. Pulsing or changes in fan size may be caused by:

• Blocked filters
• Restricted suction hoses
• Air entering the system
• Low coating levels
• Damaged or leaking hoses
• Pump wear or incorrect pump selection

Check the coating level, filters, hoses and connections. If the equipment cannot maintain pressure, the pump may require inspection or servicing.

 

6. Incorrect coating viscosity

A coating that is too thick may atomise poorly, creating a heavy or irregular pattern. Temperature and inadequate mixing can also affect how the material flows.

Follow the coating manufacturer’s instructions for mixing, application temperature, pot life and thinning. Do not add thinner simply to compensate for an equipment problem, as this may affect application, curing and final performance.

 

7. Air cap problems

On conventional, HVLP and some air-assisted systems, blocked or damaged air-cap passages can make the pattern heavier at the top, bottom or one side.

Clean the air cap using the manufacturer’s recommended tools and products. Replace damaged components rather than trying to modify them.

Poor-quality or fluctuating compressed air can also affect atomisation. Air filters, regulators, separators and drains should therefore be inspected and maintained regularly.

 

8. Inconsistent operator technique

Equipment may be working correctly, but changes in gun movement can still create an uneven finish.

Common problems include:

• Changing the distance from the surface
• Tilting or arcing the gun
• Moving too quickly or slowly
• Spraying at an unsuitable angle
• Inconsistent overlap between passes

Keep the gun perpendicular to the surface and move it parallel to the workpiece. Maintain a steady distance, speed and overlap throughout each pass. We would also recommend maintaining a consistent angle, distance and pace to achieve uniform coverage.

When an uneven spray pattern appears:

1. Stop and examine the test pattern.
2. Check that the coating is correctly mixed and within its pot life.
3. Inspect the coating supply, hoses and connections.
4. Clean the filters according to the manufacturer’s guidance.
5. Check the tip, nozzle and air cap for blockages, wear or damage.
6. Confirm that the tip is suitable for the coating and equipment.
7. Adjust the pressure gradually.
8. Review gun distance, angle, speed and overlap.
9. Carry out another test spray before restarting work.

Always isolate the equipment and follow the manufacturer’s pressure-relief instructions before removing or inspecting components. High-pressure fluid from airless equipment can cause serious injection injuries.

Routine spray equipment maintenance can prevent many pattern problems. This should include cleaning tips and air caps, replacing worn parts, checking filters and hoses, maintaining pumps and regulators, and servicing compressed-air filtration.

Operators should also test the spray pattern whenever the coating, tip, pressure or application conditions change. Recording recurring faults can help identify components that require more frequent maintenance.

An uneven spray pattern usually indicates a problem with the tip, pressure, coating supply, material preparation, equipment condition or operator technique.

By checking these areas methodically, operators can reduce overspray, control coating consumption and achieve more consistent results.

Airblast supplies industrial spraying equipment, replacement parts and servicing support for a wide range of applications. If spray pattern problems continue after basic checks, contact the Airblast team for advice on equipment selection, inspection or maintenance.