Why do bubbling and peeling occur after repainting?

During automotive refinishing, industrial equipment refurbishment, secondary spraying of wood furniture, and steel structure maintenance, many applicators encounter the following issue:

• Bubbling after recoating
• film peeling
• Poor interlayer adhesion
• local blistering
• Increased pinholing
• coating delamination

Many people's first reaction would be to think that:

• It is a construction technical issue.
• The substrate preparation was inadequate.
• The paint quality is poor.

In reality, in many cases, the core factor that truly affects the recoating performance often stems from "imbalance in the additive system."

In particular:

• leveling agent
• defoamer
• dispersant

If the selection is unreasonable or the addition amount is abnormal, either may directly affect interlayer adhesion.

This article systematically analyzes the causes of blistering and delamination upon recoating, as well as solutions in industrial coatings.

I. What is intercoat adhesion for recoating?

The so-called interlayer adhesion refers to:

Adhesion between a newly applied coating and the old paint film.

If interlayer adhesion is insufficient, the following issues are prone to occur:

• blistering
• delamination
• Cracking
• complete flaking

It is more likely to occur especially in the following scenarios:

• automotive touch-up paint
• Industrial equipment refurbishment
• Wood coating second application
• anti-corrosion paint maintenance works

II. Why do additives affect recoat performance?

Many people think of additives merely as "auxiliary materials."

In fact, in modern coating systems, additives are critical for:

• leveling
• defoaming
• dispersion
• wetting
• anti-cratering
• surface tension control

all play important roles.

However, more additives are not necessarily better.

If the ratio is imbalanced, it will instead compromise the stability of the paint film.

3. Why does excessive leveling agent lead to reduced adhesion?

The main function of the leveling agent is:

• Improve film leveling
• Reduce orange peel
• enhance gloss

However, if added in excess:

The paint film surface will become excessively smooth.

This will result in:

The new paint cannot effectively "grip" the old paint layer.

Thereby resulting in:

• interlayer adhesion reduction
• Poor intercoat adhesion
• Late-stage cracking and delamination

It is especially pronounced in high-gloss automotive coatings and high-gloss wood coatings.

4. Why can excessive defoamer lead to bubbling and blistering?

Defoamer is used to eliminate bubbles generated during the construction process.

Under normal conditions, it can improve the quality of the paint film.

However, if added in excess:

May form:

• micropore
• pinhole
• local void

When recoating:

Solvents in the new paint will penetrate into the old paint film along these micropores.

Subsequently produced:

• blistering
• localized blistering
• coating delamination

This risk is particularly higher in high-build industrial coatings.

5. What problems can be caused by an imbalance of dispersant?

The dispersant is mainly responsible for:

Ensure the pigment is uniformly dispersed in the system.

If the dispersion system is unstable:

Prone to:

• pigment agglomeration
• uneven color paste
• local stress concentration

This will reduce:

• overall adhesion of the paint film
• Mechanical properties
• interlayer stability

ultimately affecting the adhesion of the recoat.

6. Why do the same paints show significant performance differences between different manufacturers?

Many users will find that:

Similar products:

• Some have good recoat stability.
• Some are prone to delamination.
• Some are prone to blistering.

The core difference usually lies in:

balance capability of the additive system

A truly mature coating manufacturer will address:

• resin system
• solvent evaporation rate
• surface tension
• additive compatibility

Perform system balancing.

This is also one of the key cores of industrial coating technology.

7. Which industries are most prone to repainting issues?

1. Automotive refinish paint

Automotive touch-up painting has very high requirements for intercoat adhesion.

If the substrate is too slippery or additive migration is severe:

Prone to:

• varnish delamination
• edge lifting
• local blistering

2. Industrial Anti-Corrosion Renovation

After long-term use of industrial equipment:

The old paint film has aged.

If repainted directly:

Prone to:

• poor adhesion
• coating delamination
• localized peeling

It is particularly common in epoxy systems.

3. Secondary application of wood coatings

Wood surfaces are generally relatively smooth.

If repainted without sanding:

Prone to:

• bite-through
• delamination
• film cracking

8. How to Resolve Blistering and Peeling Issues in Repainting?

Solution 1: Strictly control the addition level of additives

Additives must be precisely controlled according to the formulation.

It must not be arbitrarily increased based on experience.

In particular:

• leveling agent
• defoamer
• wetting agent

Excessive use will affect the stability of the system.

In modern industrial production, it is usually achieved through:

• small-scale test verification
• Compatibility testing
• Recoat test

Determine the optimal addition ratio.

Solution 2: Perform sanding treatment before recoating

Sanding is an important step to improve intercoat adhesion.

Proper sanding can:

• increase surface roughness
• improve mechanical adhesion
• Remove surface contamination layer

Common methods include:

• dry sanding
• water grinding
• scouring pad treatment

Different systems require matching different roughness levels.

Solution 3: Use the matching additive system

Between additives from different manufacturers:

Not necessarily fully compatible.

If mixed arbitrarily:

May cause:

• surface tension conflict
• stratification
• cratering
• adhesion loss

Therefore, it is recommended that:

Use products from the same system whenever possible.

Especially in:

• Automotive paint
• UV coatings
• high-gloss wood finish

More important.

IX. How Modern Industrial Coatings Optimize Recoatability?

Currently, high-performance industrial coatings typically focus on optimizing:

1. Interlayer wetting ability

Improve the wetting performance of the new coating on the old coating.

2. Surface Tension Balance

Avoid interfacial delamination.

3. Solvent evaporation gradient

Reduce solvent shock to the old paint film.

4. Additive Migration Control

Reduce the issue of surface additive enrichment.

X. How to Reduce Repainting Rework Rate?

For construction companies, repainting failures will increase:

• Labor cost
• material loss
• rework time
• engineering risk

Therefore, it is recommended to establish a standardized construction process.

Including:

• Fixed grinding standard
• fixed recoat interval
• fixed dilution ratio
• fixed spray thickness
• Fixed ambient temperature and humidity

This effectively enhances construction stability.

Conclusion

Blistering, peeling, and bubbling after paint recoating are essentially often related to an imbalance in the additive system and insufficient interlayer adhesion.

Whether for automotive refinishing, industrial anti-corrosion renovation, or secondary wood coating application, a high-quality coating system is inseparable from:

• rational additive balance
• stable resin system
• scientific construction technology
• Good substrate preparation

A truly mature coating manufacturer will often enhance film stability and long-term recoatability through precise additive control, thereby achieving more reliable application results and product quality.