Airless spraying is suited to large areas and thick-film coating.
It is used for building materials, steel structures, tanks, piping, machine frames, large components, and corrosion-protection coatings.

Air spraying uses compressed air to atomize paint.
Airless spraying instead forces paint through a nozzle at high pressure, using that force to break it into fine droplets for application.

This method readily delivers large quantities of paint and builds thick films.
It is therefore an effective option where greater application efficiency is required or where corrosion protection requires a minimum film thickness.

However, the benefits of airless spraying go beyond simply being convenient for thick application.
Unless nozzle selection, pressure, paint viscosity, working distance, gun speed, and film thickness are properly controlled, sagging, uneven film thickness, rough finish, missed areas, excessive thickness, and paint losses can occur.

Airless spraying is a powerful tool.
That makes proper control essential to prevent substantial quality defects.

1. What Is Airless Spraying?

Airless spraying is a coating method that ejects paint through a nozzle at high pressure and atomizes it without air.

Here, “airless” does not mean that no air is used anywhere; it means that compressed air is not the main force used to atomize the paint.

A pump pressurizes the paint, which is ejected at high speed through a small nozzle opening.
The pressure difference spreads the paint into a spray that is applied to the workpiece.

Airless spraying has the following characteristics.

• Suitable for thick-film coating
• Suitable for large-area coating
• Handles high-viscosity paints readily
• Makes it easier to increase application speed
• Well suited to corrosion-protection coatings
• Can reduce overspray under some conditions
• However, nozzle and pressure control become important

Airless spraying is a method for both increasing application efficiency and achieving the required film thickness.

2. Why Airless Spraying Excels at High Film Build

Compared with air spraying, airless spraying readily deposits more paint in a single application.

It is therefore suitable for the following applications.

• Corrosion-protection coatings
• Primer application
• Large structures
• Steel members
• Tanks
• Piping
• Building materials
• Machine frames
• Components specified for thick-film coating

In corrosion-protection coatings, film thickness can directly affect performance.
If the specified thickness is not achieved, rust protection may be inadequate.

However, excessive thickness also causes problems.
An excessively thick film can cause poor drying, solvent popping, sagging, cracking, or insufficient curing within the film.

The ability to apply thick films is therefore an advantage of airless spraying, but it also brings a risk of excessive thickness.

Precisely because this method excels at high film build, film-thickness control is essential.

3. The Nozzle Determines Quality

The nozzle is extremely important in airless spraying.

It determines paint output, spray-pattern width, and how the paint strikes the coating surface.
A nozzle in poor condition makes the finish unstable even when the paint itself is normal.

Check the following nozzle-related points.

• Nozzle orifice size
• Spray-pattern width
• Wear condition
• Clogging
• Chipping
• Adhering foreign matter
• Hours of use
• Cleaning condition

Nozzle wear can increase output or distort the spray pattern.
This can produce excessive film thickness, streaks, or uneven paint deposition.

A clogged nozzle can eject paint unevenly to one side, causing uneven coverage or streaks.

In airless spraying, nozzles are consumable items.
Manage them as components that affect quality, rather than continuing to use them simply because they still function.

4. Higher Pressure Is Not Always Better

Airless spraying ejects paint at high pressure.
However, increasing the pressure does not necessarily improve results.

Excessively high pressure can cause the following problems.

• Paint mist becomes too fine and disperses
• Paint losses increase
• The surface becomes gritty
• Paint rebounds from the coating surface
• Overspray increases
• Nozzle wear accelerates
• Workplace safety risks increase

If pressure is too low, atomization is inadequate and the following problems occur.

• The spray pattern becomes distorted
• Streaks appear
• The finish becomes rough
• Film thickness becomes uneven
• Areas remain uncoated
• Edges receive insufficient film thickness

Pressure must be set to suit paint viscosity, nozzle orifice size, required film thickness, and workpiece geometry.

The important point is not to maximize pressure.
It is to establish conditions that atomize the paint consistently and achieve the specified film thickness without difficulty.

5. Film Thickness Can Increase Rapidly in Airless Spraying

Because airless spraying has a high output, even a small change in working conditions can significantly change film thickness.

The following conditions are particularly influential.

• Gun distance
• Gun speed
• Pass overlap
• Nozzle orifice size
• Pressure
• Paint viscosity
• Operator posture
• Workpiece geometry

Moving the gun just a little more slowly increases film thickness.
Too much overlap at the same location creates excessive thickness.
Corners and edges may accumulate more paint.

Excessive film thickness causes poor drying or sagging.
Solvent may also remain inside the film and later cause solvent popping or blistering.

Since airless spraying can achieve the required film thickness in one application, controlling excessive deposition in that application is also important.

6. Sagging Requires Particular Attention in Thick-Film Coating

Since airless spraying readily builds thick films, some conditions also make sagging more likely.

Sagging commonly occurs in the following situations.

• Too much paint is applied in one pass
• Gun movement is slow
• The gun is too close
• Viscosity is low
• The paint is over-thinned
• Drying is slow
• Vertical surfaces receive a thick film
• Excessive overlap occurs at corners or edges

Achieving film thickness is sometimes the main objective of airless spraying.
However, trying to apply the specified thickness all at once can cause sagging or poor drying.

When a thick film is required, design the number of coats, drying time, and recoating conditions rather than forcing the full thickness into one application.

7. Investigate Pattern Defects Through the Nozzle, Pressure, and Paint Condition

A stable spray pattern is important in airless spraying.

A normal pattern spreads paint evenly.
A distorted pattern produces uneven film thickness or streaks.

When pattern defects occur, check the following.

• Is the nozzle worn?
• Is the nozzle clogged?
• Is foreign matter clogging the filter?
• Has the paint been adequately filtered?
• Is the pressure too low?
• Is paint viscosity too high?
• Is there foreign matter or pressure fluctuation in the hose?
• Is the pump pulsating?

Before treating a pattern defect as a paint defect, check the nozzle, pressure, and supply system.

8. Safety Management Is Particularly Important in Airless Spraying

Airless spraying ejects paint at high pressure.
Safety management is therefore extremely important.

High-pressure paint is dangerous if it strikes the skin.
Even an injury that looks small may involve paint being injected into the body under high pressure.
This can result in a serious accident.

The following controls are therefore necessary.

• Never point the gun tip at a person
• Always release pressure before cleaning the nozzle
• Check pressure before and after work
• Wear protective equipment
• Check high-pressure hoses for deterioration
• Do not operate equipment when a leak is present
• Provide safety training for operators
• Define emergency response procedures

Airless spraying is efficient, but it must always be treated as high-pressure equipment.

The “care” that CoatureVietnam values also means creating processes in which operators can work safely.

9. Common Problems in Airless Spraying

The following problems commonly occur in airless spraying.

Airless-spraying defects must therefore be considered through the combination of nozzle, pressure, film thickness, and drying conditions.

10. Basic Shop-Floor Checklist

Check the following items to stabilize airless spraying.

1. Nozzle Type

Check that the nozzle suits the required film thickness, paint viscosity, and coating area.

2. Nozzle Wear

A worn nozzle changes the output and distorts the pattern.
Define operating-hour limits and replacement criteria.

3. Pressure Setting

Check that the pressure atomizes the paint consistently.
Pressure that is too high or too low leads to defects.

4. Paint Viscosity

Excessively high viscosity makes atomization difficult; excessively low viscosity makes sagging more likely.

5. Filter Control

Foreign matter in the paint causes nozzle clogging or streaks.
Filters and paint filtration must be managed.

6. Film-Thickness Measurement

Check that film thickness meets the specification and is not excessive.

7. Drying Conditions

Since thick films build readily, watch for insufficient drying and solvent remaining inside the film.

8. Safety Management

Thoroughly implement pressure release, protective equipment, hose inspections, and operator training for this high-pressure equipment.

11. Improvements That Stabilize Airless Spraying

The following improvements help stabilize airless-spraying quality.

Select Nozzles for Each Product

Rather than coating every product with the same nozzle, select it according to product size, required film thickness, and paint viscosity.

Define Nozzle Replacement Criteria

Nozzles wear.
Continuing to use a worn nozzle increases paint consumption and causes uneven film thickness.

Standardize Pressure Conditions

Quality is unstable when pressure settings differ between operators.
Define standard pressures and enable them to be recorded.

Make Film-Thickness Measurement Routine

Film thickness can be difficult to judge visually in airless spraying.
Measure it to identify excessive or insufficient thickness.

Control Filters and Paint Filtration

Filter control and paint filtration are important for preventing nozzle clogging and streaks.

Review Drying Conditions for Thick Films

For thick application, check drying time, flash-off, and heating conditions.
Rapid heating may cause defects if solvent inside the film cannot fully escape.

Provide Safety Training

Airless spraying uses high-pressure equipment.
Safety training is as important as quality training.

12. Standardization Also Reduces the Burden on Operators

Airless spraying efficiently coats large areas.
However, without standardized conditions, operators must adjust settings based on experience and intuition.

Quality then depends on individual operators.
Their workload also increases.

The following standardization is needed.

• Nozzles by product
• Pressures by product
• Film-thickness standards by product
• Gun distance
• Gun speed
• Pass overlap
• Drying conditions
• Nozzle replacement criteria
• Filter replacement criteria
• Safe work procedures

Standardization is not intended to constrain operators.
It provides a foundation for confident work and consistent quality.

13. Conclusion: Airless Spraying Requires Control Precisely Because It Excels at High Film Build

Airless spraying is effective for thick-film coating, large areas, and corrosion protection.
It offers high application efficiency and makes it easier to achieve the required film thickness.

However, its ability to build thick films requires attention to excessive thickness, sagging, poor drying, and uneven film thickness.

The basic checks for airless spraying are as follows.

• Is the nozzle appropriate?
• Is the nozzle free from wear?
• Is the pressure appropriate?
• Is paint viscosity suitable?
• Is the filter free from clogging?
• Is film thickness within the specified range?
• Are drying conditions suited to thick films?
• Is safety management thoroughly implemented?

Airless spraying is a powerful coating method.
The more powerful the method, the more important proper control becomes.

Coating the Future with Science and Care

Science means controlling the nozzle, pressure, film thickness, and drying conditions numerically.
Care means establishing a process in which operators can consistently produce good products safely and without undue strain.

CoatureVietnam examines airless spraying as a process encompassing paint, nozzles, pressure, film thickness, drying, and safety, rather than simply as a spraying-equipment issue.

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