Coating factories generate waste paint and waste thinner.

Using paint leaves some surplus.
Color changes require cleaning thinner.
Booth operation generates mist or paint residues.
Two-component paint left unused after mixing becomes waste.

Waste paint and thinner may therefore seem unavoidable in coating factories.

However, treating all of it as inevitable waste overlooks improvement opportunities.

Waste paint was originally purchased paint.
Waste thinner was originally purchased thinner.
More waste therefore means purchased materials are not becoming product value and also incur treatment costs before leaving the factory.

Reducing waste paint and thinner requires more than examining treatment methods.
The important point is to examine the sources.

Which processes generate waste paint, and why?
Which tasks increase waste thinner, and why?
Returning to these questions is the starting point for waste reduction.

1. Waste Paint and Thinner Are Both Environmental and Cost Issues

Waste paint and thinner require environmental management.

They must be stored, segregated, and handed over to treatment contractors appropriately.
Management must also follow applicable laws and internal rules.
Odors, VOCs, fire risks, and leakage risks require attention.

However, there is more to consider.

Waste paint and thinner are also cost issues.

Large waste-paint quantities may indicate excessive paint purchasing.
Large waste-thinner quantities may indicate excessive use for cleaning or dilution.
Higher waste-treatment costs raise coating costs.
Storage areas, containers, management records, and handling work also cost money.

Reducing waste therefore protects coating-process profitability as well as reducing environmental impact.

2. First Identify Where Waste Is Generated

The first step in reducing waste paint and thinner is to identify where they are generated.

Factory-wide monthly kilograms or liters alone do not reveal the cause.
Examine quantities by process, task, and color change.

Check the following sources.

• Paint mixing
• Application work
• Color changes
• Gun cleaning
• Hose and piping cleaning
• Booth cleaning
• Fixture cleaning
• Surplus-paint handling
• Recoating defective products
• Pretreatment and cleaning processes
• Prototype or small-lot production

Knowing which processes generate the most waste makes improvement priorities easier to set.

Looking only at the waste-storage area does not reveal the sources.
Return to where waste is generated.

3. Excessive Mixing Quantities Increase Waste Paint

Mixing too much paint is a major cause of waste paint.

Prepare more paint than needed.
Mix extra as a precaution.
Prepare surplus to avoid running short during work.
Determine quantities solely through experience without checking actual coating area or transfer efficiency.

These conditions increase surplus paint.

Two-component paints in particular have a limited usable period after the base and curing agent are mixed.
Once this time has passed, the paint cannot be used.
It becomes waste paint.

The following information is needed to optimize mixing quantities.

• Coating area
• Required film thickness
• Paint solids content
• Transfer efficiency
• Loss rate
• Product quantity
• Planned color changes
• Working time
• Pot life

Waste paint will not decrease if mixing quantities are determined by intuition alone.
Calculate requirements, compare them with actual consumption, and standardize mixing quantities.

4. Excessive Film Thickness Increases Paint Losses and Drying Load

Excessive film thickness is one cause of increased paint consumption.

Film thickness is the thickness of the coating film.
Achieving the required thickness is important.
An excessively thin film may cause problems in hiding power, rust resistance, durability, or appearance quality.

However, applying more than necessary is also a problem.

Excessive thickness has the following effects.

• Paint consumption increases
• Drying time becomes longer
• Sagging becomes more likely
• Solvent popping or pinholes may appear
• Internal film drying is delayed
• Drying-oven load increases
• Defect-related rework may increase

Excessive thickness therefore wastes both materials and energy.

Film-thickness control is important for reducing waste paint.
Check application techniques by operator, gun distance, air pressure, output, workpiece geometry, and fixture position for application beyond the required thickness.

5. Low Transfer Efficiency Turns Paint into Waste Rather Than Product

Not all sprayed paint deposits on the product.

Paint that misses the product flows toward the booth.
It remains on filters, in booth water, on floors, fixtures, or ducts, or as sludge.

This is paint loss.

Low transfer efficiency increases the following costs.

• Paint purchasing
• Booth cleaning
• Filters
• Sludge treatment
• Waste treatment
• Working time
• Thinner consumption

Improving transfer efficiency requires the following perspectives.

• Is spray distance appropriate?
• Is air pressure too high?
• Is output appropriate?
• Do gun conditions suit workpiece geometry?
• Could electrostatic coating be used?
• Are automatic-coating conditions appropriate?
• Do fixtures or hanging arrangements make coating easy?
• Are there variations between operators?

Paint flowing into the booth rather than depositing on products is a quality, cost, and environmental issue.

6. Poor Color-Change Sequencing Increases Waste Thinner

Color changes are a major cause of waste thinner.

Color changes involve cleaning guns, cups, hoses, piping, and sometimes areas around the booth.
Thinner is used for this cleaning.

More color changes mean more cleaning cycles.
More cleaning cycles increase waste thinner.

Color-change sequence is important here.

For example, switching to a completely different color each time increases cleaning load.
Dark-to-light changes require thorough cleaning.
Cleaning load may also increase after metallic or special colors.

Improved sequencing may reduce cleaning quantities.

For example, consider the following approaches.

• Run from light to dark colors
• Group similar colors
• Group the same paint systems
• Run special colors last
• Group small-lot products
• Reduce color changes with high cleaning loads

Unlinked production and coating plans increase color-change frequency.
Production sequence also needs examination to reduce waste thinner.

7. Unstandardized Cleaning Methods Increase Waste Thinner

Thinner consumption can differ greatly between operators even for the same cleaning task.

One operator cleans with a small amount.
Another uses a large amount.
Decisions on cleaning completion differ.
Fresh thinner is always used regardless of contamination level.
Initial and final cleaning are not separated.

These conditions prevent waste-thinner reduction.

Standardized cleaning requires defining the following items.

• Cleaning procedure
• Guideline thinner quantity
• Separation of initial and final cleaning
• Cleaning-completion criteria
• Permitted reuse of cleaning thinner
• Waste-thinner segregation method
• Cleaning-container management
• Records after work

Staged use of cleaning thinner is particularly effective.

Use fresh thinner for final cleaning.
Use previously used thinner for intermediate cleaning.
Use dirty thinner for initial cleaning.
Finally collect it as waste thinner.

Separating uses this way may reduce fresh-thinner consumption and waste-thinner quantities.

8. Keep Waste-Thinner Streams Separate

Segregation is also important for reducing waste thinner.

Putting all waste thinner into one container makes reuse or reclamation difficult.

For example, waste-thinner streams include the following.

• Relatively clean cleaning thinner
• Waste thinner with high paint content
• Waste thinner containing water
• Waste thinner containing paints from different resin systems
• Waste thinner used for cleaning areas
• Waste thinner potentially suitable for reclamation and reuse
• Waste thinner requiring disposal

Mixing these together turns potentially reusable material into waste too.

Segregation requires clear shop-floor rules.

• Use separate containers
• Provide clear labels
• Use color coding
• Define storage locations
• Identify materials that must not be mixed
• Define collection frequency
• Assign management responsibility

Separate waste thinner when it is generated rather than sorting it after collection.

9. Recoating Defects Increases Waste Paint and Thinner

Defective products require repair or recoating.

Recoating uses additional paint.
Cleaning guns or containers uses additional thinner.
The oven is used again.
Inspection is repeated.

Defects therefore increase waste.

The following defects particularly increase rework.

• Contamination and dirt nibs
• Sagging
• Cissing
• Uneven color
• Insufficient film thickness
• Poor gloss
• Insufficient drying
• Poor adhesion
• Scratches

Reducing the defect rate is also important for reducing waste paint and thinner.

Environmental and quality improvements are connected.
Stable quality reduces rework, material losses, and waste.

10. Small-Lot, Multicolor Production Is Prone to More Waste

Small-lot, multicolor production tends to increase waste paint and thinner.

The reasons are clear.

Frequent color changes.
Small mixing quantities that readily leave surplus.
Leftover dedicated colors.
Frequent cleaning.
Larger paint inventories.
More expired paint.
Risk of confusing similar colors.

These workplaces need the following measures to reduce waste.

• Optimized color-change sequencing
• Standardized mixing quantities
• Measurement rules for small lots
• Surplus-paint management
• Organization of similar colors
• Inventory control for infrequently used colors
• Shelf-life control for dedicated paints
• Visibility of materials scheduled for disposal

Small-lot, multicolor production needs flexibility.
However, leaving that flexibility entirely to shop-floor judgment increases waste.

Standardize what can be standardized and clarify decisions that require judgment.

11. Make Waste Quantities Visible

Reducing waste paint and thinner first requires making quantities visible.

How much is generated per month?
Which lines generate more?
Which color changes generate more?
Where do operators differ?
Which products generate more?
Which defects increase recoating?
What are treatment costs?

Without visibility, improvement effects cannot be assessed.

Make the following items visible.

• Waste-paint quantity
• Waste-thinner quantity
• Cleaning-thinner consumption
• Surplus-paint quantity
• Paint purchasing quantity
• Number of products coated
• Number of color changes
• Number of defect-related recoating operations
• Waste-treatment costs
• Thinner purchasing costs

Data do not have to be perfect from the start.
Simple records are a suitable starting point.

The important point is to assess waste numerically rather than by intuition.

12. CoatureVietnam’s Checkpoints for Reducing Waste Paint and Thinner

CoatureVietnam regards waste-paint and waste-thinner reduction as more than waste treatment.

We examine the following perspectives.

Mixing

Are mixing quantities appropriate?
Is too much two-component paint being prepared?
Is surplus paint managed?

Application

Is film thickness appropriate?
Is transfer efficiency low?
Are spray conditions appropriate?
Do operators differ?

Color Changes

Are color changes excessive?
Can sequencing be improved?
Are changes with high cleaning loads frequent?

Cleaning

Are procedures standardized?
Could cleaning thinner be used in stages?
Is waste thinner segregated?

Quality

Does defect-related recoating increase waste?
Are defects examined in relation to waste quantities?

Inventory

Are small-lot colors or surplus paint becoming waste?
Is paint expiring?

Management

Are waste quantities, treatment costs, and sources assessed numerically?

These checks connect waste reduction with process, quality, and cost improvement.

Conclusion

Looking only at waste-storage areas is insufficient for reducing waste paint and thinner.

Examine the sources.

Why was paint left over?
Why was so much thinner used?
Why are color changes frequent?
Why does cleaning take time?
Why is film thickness excessive?
Why is recoating increasing?
Why is waste thinner not segregated?

Returning these questions to the process reveals starting points for improvement.

Waste paint was originally purchased paint.
Waste thinner was originally purchased thinner.
If they fail to become product value and incur disposal costs, there is room for improvement.

CoatureVietnam assesses waste paint and thinner as cost losses in the coating process, as well as environmental issues.
We trace them back through mixing, application, cleaning, color changes, rework, and inventory control to support waste reduction at its source.

Coating the Future with Science and Care
Reducing waste is a practical improvement that reduces shop-floor workload and factory costs while benefiting the environment.