1. What Is Coating Lifting?

1.1 Definition of Coating Lifting

Coating lifting refers to a defect that occurs during multi-layer coating application or repainting of old paint films. Solvents, co-solvents, or thinners in the upper coating penetrate into the underlying coating film, causing the lower film to soften, become plasticized, swell, or partially re-dissolve. This reduces the cohesive strength of the lower coating film and destabilizes interlayer adhesion, eventually leading to defects such as wrinkling, blister-like lifting, edge curling, and delamination.

1.2 Typical Manifestations of Lifting

1.3 Difference Between Lifting and Poor General Adhesion

Poor general adhesion is usually associated with substrate contamination, low surface energy, insufficient sanding, inadequate surface roughness, or poor intercoat cleaning. Lifting, by contrast, emphasizes solvent attack by the upper coating on the lower coating film.

2. Physicochemical Nature of Lifting: Solvent Penetration, Resin Swelling, and Stress Instability

2.1 Basic Process of Lifting

Lifting can be understood as a continuous physicochemical process:

Application of the upper coating → solvent enters the lower coating film → the lower resin is plasticized, swollen, or partially re-dissolved → cohesive strength of the lower layer decreases and interlayer adhesion becomes unstable → drying shrinkage of the upper layer becomes unsynchronized with swelling deformation of the lower layer → wrinkling, lifting, edge curling, and delamination occur.

Lifting is not caused by a single factor. It results from the combined effects of solvent migration, resin swelling, drying shrinkage, and interlayer stress.

2.2 Solvent Penetration

Immediately after the upper coating is applied, the wet film contains a high solvent concentration and has strong fluidity. At this stage, if the lower coating film has not fully cured, has insufficient crosslink density, is excessively thick, or contains sand-through areas, solvent can easily diffuse into the lower layer.

After entering the lower coating film, the solvent changes the interactions between resin chain segments. For resins with poor solvent resistance, the solvent does not merely remain on the surface; it may penetrate into the coating film and cause significant softening and swelling.

2.3 Plasticization

Plasticization is an important intermediate stage in the formation of lifting. After solvent enters the polymer coating film, it weakens the interactions between resin chain segments, increases chain mobility, and reduces coating hardness, modulus, and cohesive strength.

From a materials-performance perspective, solvent plasticization usually lowers the Tg, or glass transition temperature, of the coating film. A film that originally appears “dry” may become soft, tacky, or lose its resistance to deformation under the action of solvent.

2.4 Swelling and Partial Re-Dissolution

If the upper-layer solvent has strong compatibility with the lower-layer resin, the lower coating film may progress from plasticization to swelling, and in severe cases, partial re-dissolution may occur. This step is the key distinction between lifting and ordinary intercoat adhesion problems.

In most lifting cases, the resin backbone does not undergo chemical degradation. Instead, the problem is the uncontrolled diffusion, plasticization, swelling, and re-dissolution of the polymer coating film by solvent.

2.5 Stress Instability

During drying, the upper coating undergoes solvent evaporation and volume shrinkage. If the lower coating film simultaneously swells, softens, and loses strength, the direction of volume change and the mechanical state of the upper and lower layers become inconsistent. This inconsistency creates two types of stress:

① Shrinkage stress: drying shrinkage of the upper coating film;

② Swelling stress: volume expansion of the lower coating film after absorbing solvent.

When the cohesive strength of the lower coating film or the interlayer adhesion cannot resist these stresses, wrinkling, lifting, edge curling, or peeling occurs.

The physicochemical essence of lifting can be summarized as:

Lifting = solvent penetration + resin plasticization/swelling/re-dissolution + reduced coating-film strength + interlayer stress instability.

3. Why Does the Upper Coating “Lift” the Lower Layer?

Whether the upper coating causes lifting mainly depends on three factors: solvent strength, instantaneous solvent load, and solvent residence time.

3.1 Solvent Strength

Solvent strength refers to the ability of solvents in the upper coating to dissolve, swell, or plasticize the lower-layer resin. If the solvent in the upper coating can effectively dissolve its own resin while also having strong compatibility with the lower-layer resin, lifting may occur.

This risk is especially high when the lower layer is a thermoplastic resin, an insufficiently cured resin, or an old paint film with unknown composition.

Common high-risk situations include:

Strong-solvent content is too high;

the thinner is improperly selected;

the topcoat solvent has strong swelling ability toward the primer resin;

excess thinner is added during application;

a fast-drying strong-solvent system is applied over an old film with poor solvent resistance.

It should be noted that lifting risk cannot be judged simply by assuming that “a certain solvent class is always strong” or “a certain solvent class is always weak.” In real systems, solvent aggressiveness depends on the solvent combination, lower-layer resin type, curing state, film thickness, and application conditions.

HSP, or Hansen Solubility Parameters, is an important tool for analyzing compatibility between solvents and resins. HSP divides material interactions into three components:

The basic idea of HSP is that if a solvent and a resin are close to each other in three-dimensional HSP space, they are more likely to dissolve, swell, or be compatible with each other. If they are far apart, the tendency toward dissolution or swelling is weaker.

In lifting analysis, the value of HSP lies in determining whether the solvent package of the upper coating is close to the swelling or dissolution region of the lower-layer resin. A solvent package, or mixed solvent system, refers to the overall solvent combination formed by the main solvents, co-solvents, thinners, and solvents with different evaporation rates in the upper coating.

For example, a solvent package may be suitable for the resin in the upper coating. However, if it is also close to the HSP region of a lower-layer thermoplastic acrylic, nitrocellulose coating, or insufficiently cured alkyd resin, it may soften the lower layer and cause lifting.

HSP can be used for formulation screening:

① Selecting solvents that meet the application and film-forming requirements of the upper coating;

② Avoiding solvent packages that have excessive swelling ability toward the lower-layer resin;

③ Adjusting the overall HSP position through mixed solvents;

④ Comparing the attack risk of different thinners toward old films.

HSP alone cannot determine whether lifting will occur. Actual lifting is also affected by evaporation rate, wet-film thickness, flash-off time, curing degree of the lower layer, and application environment.

3.3 Instantaneous Solvent Load

Instantaneous solvent load refers to the amount of solvent and solvent activity delivered by the upper wet film to the lower coating film at the moment of application. It determines how strong the solvent attack on the lower layer is within a short period.

When the upper coating is applied too wet in a single pass, when the wet film is too thick, or when multiple coats are applied continuously, the total amount of solvent contacting the lower layer within a short time increases. This strengthens the driving force for downward solvent diffusion and significantly increases the risk of lifting.

High instantaneous solvent load is commonly associated with:

Direct wet spraying in the first pass;

insufficient flash-off between coats;

continuous high-build application;

excessive thinner addition;

spray distance being too short or paint output being too high;

direct application of a strong-solvent topcoat over a sensitive old film.

With the same formulation, multiple thin coats may not cause lifting, whereas one overly wet coat may immediately cause wrinkling. This shows that lifting is determined not only by solvent type, but also by the amount of solvent contacting the lower layer per unit time.

3.4 Evaporation Rate and Residence Time

The relationship between solvent volatility and lifting cannot be simplified as “fast-drying is safe” or “slow-drying is dangerous.” The key lies in the duration of solvent attack on the lower layer and the pathway through which solvent is released.

During coating-film drying, solvent evaporation, increasing polymer concentration, diffusion limitation, and drying shrinkage jointly affect internal stress in the coating film. If the surface forms a dense layer too early, internal solvent release becomes difficult. The lower layer may then remain under continuous solvent disturbance, increasing the risk of lifting and wrinkling.

Solvent-induced lifting does not depend only on whether the solvent has strong dissolving power. It also depends on whether the instantaneous load is too high, whether the residence time is too long, and whether solvent release is smooth.

4. Why Is the Lower Coating Film Susceptible to Lifting?

Whether the lower coating film is easily affected mainly depends on its resin type, curing degree, crosslink density, film thickness, residual solvent, and old-film condition.

4.1 Re-Dissolvable Resins and Reaction-Cured Resins

Different resin systems vary greatly in their sensitivity to lifting. The core difference lies in whether the dry film can be readily re-opened by solvent.

The sensitivities listed in the table are relative trends under common formulations and normal curing conditions. Actual risk must be judged based on specific resin structure, crosslink density, curing conditions, film thickness, and recoating process.

Re-dissolvable systems such as nitrocellulose coatings and thermoplastic acrylics may still be re-swollen or dissolved by compatible solvents after drying; therefore, they have a higher risk of lifting.

Reaction-cured systems such as epoxy, two-component polyurethane, and amino baking coatings form three-dimensional crosslinked networks after full curing. Solvents have more difficulty re-opening the coating-film structure, so these systems generally have stronger resistance to lifting. However, if the reaction has not been completed, they may still be softened or swollen by solvents in the upper coating.

4.2 Curing Degree

Insufficient curing is one of the most common lower-layer causes of lifting. When the lower layer is not fully cured, the coating film may have the following problems:

① High mobility of resin chain segments;

② Crosslinked network not yet fully formed;

③ Low cohesive strength;

④ High levels of residual solvent or small molecules;

⑤ Surface appears dry, but the interior has not yet reached sufficient solvent resistance.

Once solvent from the upper layer enters under these conditions, the lower layer can easily be plasticized, swollen, and disturbed.It should be noted that “dry-to-touch” is not the same as “through-dry,” and even less the same as “fully cured.” Many lifting problems occur when the base layer is no longer tacky at the surface, but the interior has not yet completed solvent release or chemical curing.

4.3 Crosslink Density

Crosslink density determines the coating film’s ability to resist solvent swelling. When crosslink density is high, resin chain segments are restricted by the network structure. Even if solvent enters the film, it is less likely to cause large-scale chain mobility and volume expansion.

When crosslink density is low, solvent can more easily loosen resin chain segments, causing the film to soften, swell, or lose cohesive strength.

However, high crosslink density does not mean lifting can never occur. Problems may still arise under the following conditions:

① Insufficient curing-agent ratio;

② Low temperature slows the reaction rate;

③ Excessive film thickness causes insufficient internal curing;

④ Recoat time is too short;

⑤ A solvent that is highly aggressive toward the resin system is used.

4.4 Film Thickness and Residual Solvent

Excessive thickness of the base layer significantly increases the risk of lifting. There are three reasons:

① Slow internal solvent release: In thick films, the solvent diffusion path is long, and residual solvent may remain inside even after the surface has dried.

② Uneven curing: The surface dries first while the interior dries later, resulting in different hardness and solvent resistance at different depths.

③ Stress is more difficult to release: Thick films are more likely to accumulate internal stress during solvent evaporation and curing, making them more prone to instability after recoating.

Therefore, for the same primer, if the film is too thick, lifting by the topcoat may occur even when the apparent recoating time seems sufficient, because the interior has not dried adequately.

4.5 Old Films and Unknown Lower Layers

Repainting old paint films is a high-incidence scenario for lifting. This is because the structure of the old film is usually unclear and may include multiple historical layers:

Nitrocellulose coating;

alkyd coating;

one-component acrylic;

old repair coating;

historical layers that were not fully cured;

different layers exposed after sanding;

surfaces contaminated by cleaning agents, oil, wax, or plasticizers.

Old film edges, sand-through areas, and feathered edges are especially susceptible to solvent penetration. Once a strong solvent from the upper layer enters between layers of the old film, localized edge curling, wrinkling, and peeling may occur.

The common characteristics of lower coating films that are easily lifted can be summarized as follows: thermoplastic, low crosslinking, insufficient curing, excessive film thickness, high residual solvent, and unknown old-film composition.

5. How to Assess the Risk of Lifting?

5.1 Qualitative Assessment Model

Lifting risk should be analyzed from four dimensions:

1. Solvent aggressiveness of the upper layer;

2. Sensitivity of the lower coating film;

3. Solvent residence time;

4. Application disturbance intensity.

These four dimensions jointly determine whether lifting will occur. During actual diagnosis, it is necessary to identify which dimension first becomes uncontrolled, and then determine the corresponding formulation or application adjustment.

5.2 Lifting Risk Diagnostic Table

5.3 Rapid On-Site Diagnostic Sequence

6. How to Reduce and Repair Lifting

To reduce the risk of lifting, control measures should be designed by reversing the lifting mechanism: reduce the solvent aggressiveness of the upper layer, lower the instantaneous solvent load, improve solvent resistance of the lower layer, control the recoat window, and confirm system safety through small-scale testing.

6.1 High Solvent Aggressiveness of the Upper Layer: Adjust the Solvent Package

In formulation design, the solvent package of the upper layer should be prevented from having excessive swelling ability toward the lower-layer resin. The following measures can be adopted:

① Reduce the proportion of strong solvents;

② Select thinners that are milder toward the lower layer;

③ Avoid solvent combinations whose HSP is too close to that of the old-film resin;

④ Adjust the dissolving power of the overall solvent package through mixed solvents;

⑤ Reduce the total solvent impact caused by excessive thinning;

⑥ Increase solids content where application performance allows, thereby reducing the solvent amount per unit area.

6.2 High Instantaneous Solvent Load: Control the Application Method

Application control is key to preventing lifting. Effective measures include:

① Use a thin coat or mist coat for the first pass;

② Avoid applying an overly wet coat in a single pass;

③ Use multiple thin coats instead of one high-build coat;

④ Extend flash-off time between coats;

⑤ Avoid continuous high-build wet-on-wet application or stacking of multiple wet films;

⑥ Lightly seal old-film edges and sand-through areas first;

⑦ Adjust thinner evaporation rate according to temperature, ventilation, and film thickness.

For sensitive lower layers, the first pass should not aim for full hiding. Instead, a thin transition layer should be formed first to reduce the chance of strong solvent entering the lower layer all at once.

6.3 Insufficient Solvent Resistance of the Lower Layer: Improve Curing Degree and Film Strength

The lower coating film must have sufficient solvent resistance and cohesive strength to withstand application of the upper coating. The following measures can be adopted:

① Extend drying or curing time of the base layer;

② Ensure accurate mixing ratios in two-component systems;

③ Ensure curing temperature and curing time meet requirements;

④ Control base-layer film thickness and avoid slow drying of thick films;

⑤ Use a sealer, intermediate coat, or barrier layer when necessary;

⑥ Avoid directly applying strong-solvent topcoats over thermoplastic old films.

For reaction-cured systems, special attention should be paid to the actual degree of curing. Low temperature, high humidity, excessive film thickness, and insufficient ventilation all delay curing and solvent release.

6.4 Improper Recoat Window: Control Recoating Timing

The recoat window directly affects lifting. If recoating is performed too early, the lower layer may not have dried or cured sufficiently and can easily be lifted by the solvent in the upper coating.

If recoating is performed too late, the lower layer may have improved solvent resistance, but interlayer bonding may decrease. If sanding, cleaning, or use of a suitable tie coat is not performed, interlayer failure may also occur.

Recoating control should follow three principles:

① Do not force recoating before the minimum recoat time;

② After exceeding the maximum recoat window, sand, clean, or use a tie coat as required;

③ Before recoating old films or unknown lower layers, perform solvent-sensitivity testing and small-area recoating verification.

6.5 Uncertain Old Film: Small-Scale Testing Is Required

Lifting risk cannot be judged solely by experience. Verification is especially necessary when dealing with new formulations, new substrates, new/old system combinations, or changing site conditions.

Small-scale testing should simulate actual application conditions as closely as possible, including film thickness, thinning ratio, spraying method, intercoat interval, drying temperature, and old-film condition.

Passing a laboratory thin-film test does not mean the system will necessarily be safe under site conditions involving thicker films or lower temperatures.

6.6 Lifting Has Already Occurred: Treat According to Failure Severity

After lifting occurs, it should not be addressed simply by applying another coat over the defect. Because the lower layer has already been softened or disturbed, further coating may worsen solvent retention and interlayer instability.

If the lower layer has clearly softened, curled, or delaminated, the reliable treatment is to remove the failed coating film rather than continue covering it with a high-build coating.

7. Representative Chemical Classification and Application Tables Related to the Nature and Control of Coating Lifting

Note: The following products are provided as representative chemical examples for studying the lifting mechanism, evaluating solvent sensitivity, screening formulations, or comparing materials. They are not equivalent to recommendations for on-site application. Actual selection, procurement, transportation, storage, use, and disposal should be based on the product SDS, COA, applicable regulations, and EHS requirements. Classifications such as “strong solvent” and “weak solvent” in the tables are relative descriptions. The specific aggressiveness depends on the target resin, solvent combination, curing state, film thickness, and application conditions.

Table 1. Products Related to Lifting Diagnosis, Solvent-Sensitivity Evaluation, and Solvent Attack

Table 2. Products Related to Solvent-Package Optimization, Evaporation Control, and Waterborne Co-Solvents

Table 3. Products Related to Film-Forming Resins, Sensitive Lower Layers, and Sealing Systems

Table 4. Products Related to Curing Agents, Crosslinkers, and Curing Catalysts

Table 5. Products Related to Adhesion Promotion, Interface Modification, and Interlayer Stability

References

[1] PPG Refinish. Lifting / Wrinkling: Common Paint Defects Guide.

[2] Sherwin-Williams Automotive Finishes. Troubleshooting Guide.

[3] Hansen Solubility Parameters. HSP Basics.

[4] Hansen, C. M. Hansen Solubility Parameters: A User’s Handbook. 2nd ed. CRC Press, 2007.

[5] Wicks, Z. W.; Jones, F. N.; Pappas, S. P.; Wicks, D. A. Organic Coatings: Science and Technology. 4th ed. Wiley, 2017.

[6] Marrion, A. R. The Chemistry and Physics of Coatings. 2nd ed. Royal Society of Chemistry, 2004.

[7] Kansai Altan. Lifting and Wrinkling.

[8] ASTM International. ASTM D5402-19, reapproved 2024: Standard Practice for Assessing the Solvent Resistance of Organic Coatings Using Solvent Rubs.

[9] Punati, V. S.; Tirumkudulu, M. S. Modeling the drying of polymer coatings. Soft Matter, 2022, 18, 214–227. DOI: 10.1039/D1SM01343B.

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