Considering deterioration, chalking, and recoating as preventive maintenance

Immediately after coating, an attractive product finish can make it seem that coating quality is satisfactory.

The color matches.
The surface is glossy.
Film thickness is within specification.
Adhesion testing is satisfactory.

These checks are certainly important.

However, coating quality should not be judged only immediately after application.

Coating films change over time in their service environment.
They gradually deteriorate under the effects of ultraviolet light, moisture, oxygen, heat, salt, chemicals, abrasion, and contaminants.

In other words, coating films have a service life.

A full assessment of coating quality must consider deterioration in service, inspections, repairs, and recoating, as well as initial quality.

Coating films deteriorate over time

A coating film is a thin protective layer formed on a substrate surface.

It has various roles.

• Improve appearance
• Provide color
• Prevent rust
• Protect against moisture
• Protect against chemicals
• Protect against ultraviolet light
• Prevent abrasion
• Extend the life of the substrate

However, a coating film does not retain the same performance forever.

An outdoor coating is exposed to sunlight, rain, humidity, heat, and oxygen.
In coastal areas, it is exposed to salt.
In industrial areas, exhaust gases, dust, and chemical mist may affect it.
Equipment components may also be exposed to abrasion, impact, cleaning, and chemical contact.

Exposure to these environments gradually deteriorates the coating film.

Deterioration progresses in stages rather than suddenly

Coating film deterioration does not happen suddenly one day.

In most cases, it progresses in stages.

Changes in appearance are often the first visible signs.

• Reduced gloss
• Fading color
• A dull surface
• Loss of sheen
• Dirt becoming harder to remove

At this stage, major peeling or rust may not yet be visible.

However, these are early signs of coating film deterioration.

As deterioration progresses, the following phenomena may appear.

• Fine cracks
• Chalking
• Blistering
• Disbonding
• Delamination
• Red rust
• Mold
• Coating film erosion

Further deterioration reduces the film’s ability to protect the substrate, leading to corrosion or deterioration of the substrate itself.

What is chalking?

Chalking is a typical form of coating film deterioration.

Chalking is the formation of a powdery surface on the coating film.
A white powder-like substance may come off on the hand when touched.

It occurs when resin components at the film surface break down under ultraviolet light, oxygen, and moisture, exposing pigments and fillers at the surface.

As chalking progresses, the film surface becomes powdery and loses gloss and color vividness.
Further progression erodes the coating film itself and reduces its ability to protect the substrate.

Chalking is more than an appearance defect.

It should be treated as a sign that the coating’s protective function is declining.

Gloss loss and fading are also signs of deterioration

Coating film deterioration is not limited to chalking.

Gloss loss and fading are also important signs.

Reduced gloss may indicate a change in the coating surface.
Fading may indicate that pigments or resin are being affected by ultraviolet light or other factors.

Gloss loss and fading may appear at an early stage, particularly in outdoor service.

Appearance alone cannot provide a complete assessment of coating film performance.
However, changes in appearance are an important starting point for understanding deterioration.

The following changes should not be overlooked during inspection.

• Has gloss decreased compared with the new condition?
• Has the color become lighter?
• Has the surface become powdery?
• Are there fine cracks?
• Is rust emerging from edges or corners?

Cracks provide an entry point for substrate deterioration

Fine cracks in a coating film may allow moisture and oxygen to enter.

The film’s role is to separate the substrate from the external environment.
Cracking reduces this barrier function.

On metal substrates in particular, moisture and oxygen can enter through cracks and promote corrosion.

Small cracks may not be noticeable.
However, leaving them untreated can lead to blistering, delamination, and rust.

Cracking in a coating film is therefore more than a cosmetic issue.

It is an important sign of deterioration that can reduce substrate protection.

Repairs become more costly once rust appears

For metal parts and structures, rust prevention is an important role of the coating film.

A sound film makes it harder for moisture, oxygen, and salt to reach the substrate directly.
However, deterioration, cracking, blistering, delamination, and insufficient film thickness make the underlying metal more susceptible to corrosion.

Repair work becomes more extensive when carried out after rust has appeared.

• Remove rust
• Remove deteriorated coating film
• Prepare the substrate surface
• Apply a primer
• Apply intermediate and topcoats as needed
• Allow sufficient drying and conditioning time
• Reinspect

If rust has progressed, the substrate itself may require repair or replacement.

Waiting until rust is conspicuous may therefore be too late.

Inspecting and repairing while film deterioration is still slight ultimately helps control costs.

Recoating does more than restore appearance

Recoating is sometimes regarded as work to restore an attractive appearance.

Restoring appearance is certainly an important purpose of recoating.

However, where coatings are intended for rust protection and durability, recoating has a broader role.

Recoating is preventive maintenance to preserve substrate protection.

If recoating is delayed until the film has fully deteriorated and the substrate is severely corroded, the repair area increases.
The work takes longer.
Costs increase.
The risks of equipment shutdown and production stoppage also increase.

Repairing while film deterioration is slight, on the other hand, may limit effects on the substrate.

Recoating should be viewed as maintenance to prevent problems from becoming serious, rather than a repair undertaken only after problems occur.

Even highly durable coatings need inspection

Highly durable paints and heavy-duty corrosion protection systems can be expected to provide long-term protection.

However, using a highly durable paint does not eliminate the need for inspection.

Coating films are affected by their service environment.

Strong ultraviolet light.
High temperature and humidity.
Salt exposure.
Chemicals.
Abrasion.
Standing water.
Dust.
Insufficient film thickness during application.
Missed edges.
Impact damage.

These factors can cause deterioration earlier than the expected service life.

Rather than simply assuming that high durability provides reassurance, it is important to consider the environment in which the durable coating will be used, how it will be inspected, and when it will be repaired.

Check regional differences in outdoor environments

Checking the service environment is very important for outdoor coatings.

Outdoor environments can differ greatly.

• General outdoor exposure
• Coastal regions
• Industrial areas
• Hot, humid regions
• Locations exposed to strong direct sunlight
• Locations with heavy rainfall
• Locations prone to standing water
• Underground
• Underwater
• Elevated locations

Different environments require different coating film performance.

The following conditions in particular need to be considered in Vietnam.

• High temperature and humidity
• Strong ultraviolet light
• The rainy season
• Salt exposure in coastal areas
• Industrial-area exhaust emissions
• Dust
• Structures with poor drainage
• Outdoor storage

A coating specification that performed satisfactorily in Japan may not perform the same way in Vietnam’s environment.

For outdoor specifications, it is important to identify the specific service location.

Classify deterioration phenomena

When checking coating film deterioration, it is important to classify the phenomena.

Describing everything as old or damaged makes it difficult to understand causes and countermeasures.

Typical deterioration phenomena include the following.

• Gloss loss
• Fading
• Chalking
• Fine cracks
• Large cracks
• Blistering
• Disbonding
• Delamination
• Red rust
• Mold
• Contamination
• Coating film erosion
• Corrosion starting at edges
• Rust starting at welds

Each has different causes and countermeasures.

Gloss loss and fading relate to ultraviolet light and the weather resistance of pigments and resins.
Blistering may involve moisture, permeation, adhesion, and surface preparation.
Red rust relates to insufficient film thickness, edge treatment, surface preparation, and rust-protection specifications.
Mold relates to humidity, the environment, cleanliness, and mold resistance.

Classifying deterioration phenomena makes it easier to choose an appropriate repair method.

Establish inspection criteria

Inspection criteria are needed to manage coating film service life.

Without them, deterioration judgments vary between people.

One person judges that the coating is still acceptable.
Another judges that it needs immediate repair.
The customer and supplier reach different conclusions.

This makes it difficult to establish an appropriate maintenance plan.

Examples of items to define in inspection criteria include the following.

• Degree of gloss loss
• Degree of fading
• Presence of chalking
• Presence of cracks
• Presence of blistering
• Presence of delamination
• Locations where rust occurs
• Extent of rust
• Remaining film thickness
• Severity requiring repair
• Severity requiring recoating

Where possible, photographic standards and check sheets are useful.

Areas to check during deterioration inspections

Coating films do not necessarily deteriorate uniformly over the whole surface.

Certain areas are particularly susceptible to deterioration.

• Corners
• Edges
• Welds
• Around bolts
• Locations prone to standing water
• Locations exposed to strong sunlight
• Locations directly exposed to rain
• Locations exposed to chemical splashes
• Locations subject to abrasion
• Locations frequently handled or contacted
• Locations where the coating tends to be thin

Inspections need to focus on these vulnerable areas as well as flat surfaces.

Edges and welds are particularly important in rust-protection applications.

Even when flat surfaces look clean, rust may be advancing from the edges.

Distinguish localized repairs from complete recoating

Deterioration does not always require complete recoating.

Depending on its severity, localized repair may be sufficient.

However, complete recoating may be needed if deterioration is widespread or substrate corrosion has progressed.

The following perspectives are needed for the decision.

• Is deterioration localized or widespread?
• Has corrosion reached the substrate?
• Is the old coating film still adhering?
• Has chalking progressed?
• Can adhesion of the repair coating be secured?
• How much existing coating must be removed?
• Are appearance differences after repair acceptable?
• How much equipment shutdown time is available?

Repair is not simply a matter of applying paint over the surface.

If deteriorated coating, a powdery surface, rust, oil, or moisture remains, the new coating film will also be unstable.

Surface preparation is very important in recoating.

Check compatibility with the old coating when recoating

Recoating requires checking compatibility with the old coating film, as well as the new paint.

What paint was used for the old coating?
How far has it deteriorated?
Is the surface chalking?
Does adhesion remain?
Will solvents in the new paint attack the old film?
Is a primer needed?
Is sanding or cleaning needed?

Without these checks, recoating may result in poor adhesion, wrinkling, blistering, or cracking.

Particular care is required when information about the existing coating is unavailable.

Recoating can be more difficult than coating a new product.
The repair specification needs to be designed after assessing the condition of the old coating film.

Organizing coating film service life through 4M + Management

CoatureVietnam also organizes coating film service life and deterioration through 4M + Management.

Material: Materials

• Does the paint’s weather resistance suit the application?
• Are rust-inhibiting pigments and primers appropriate?
• Is the topcoat’s weather resistance sufficient?
• Is compatibility with the old coating satisfactory?
• Is the substrate material susceptible to corrosion?

Method: Methods

• Is film thickness appropriate?
• Is surface preparation sufficient?
• Are edges and welds fully coated?
• Are drying and curing conditions followed?
• Is surface preparation during repair appropriate?
• Are inspection methods standardized?

Machine: Equipment

• Is blasting and sanding equipment appropriate?
• Are film thickness gauges and measuring instruments used?
• Does drying equipment suit the coating specification?
• For outdoor application, can the application environment be controlled?
• Is equipment available for safe work at height or in confined areas?

Man: People

• Do operators understand signs of deterioration?
• Can inspectors assess chalking and cracking?
• Do repair operators understand treatment of old coating films?
• Is keeping inspection records an established practice?
• Are repair criteria shared with the customer?

Management: Management

• Are inspection intervals defined?
• Are repair criteria clear?
• Is recoating scheduled?
• Is deterioration history recorded?
• Are changes in the service environment checked?
• Is this included in the maintenance budget?

Coating film life is not determined by materials alone.
It also depends on application conditions, the service environment, inspections, and repair management.

Points to check on site

Check the following when considering coating film deterioration and recoating.

• How many years have passed since the last coating application?
• Is the service environment indoors or outdoors?
• Is it coastal, industrial, or hot and humid?
• Are ultraviolet light, rain, moisture, salt, or chemicals affecting it?
• Is there gloss loss or fading?
• Does white powder come off on the hand when touched?
• Are there fine cracks?
• Is there blistering or disbonding?
• Where is rust starting?
• What is the condition of edges, corners, and welds?
• Does the old coating retain adhesion?
• Is repair sufficient, or is complete recoating needed?
• Is there a plan to remove deteriorated coating?
• What is the expected service life after recoating, in years?
• Are inspection intervals and repair criteria defined?

How CoatureVietnam can help

CoatureVietnam considers coating film deterioration and recoating as preventive maintenance, rather than simply repair work.

Paint Optimizer We assess the deterioration of existing coatings and organize paint selection, film thickness, and drying conditions needed for repair and recoating.

Paint Voyager We identify paint candidates for outdoor service, heavy-duty corrosion protection, and rust protection, and consider coating specifications suited to the service environment.

Work standards and process control We support the development of inspection criteria, repair criteria, recoating SOPs, photographic standards, and inspection checklists.

Coat Visioner We organize deterioration conditions, inspection records, and repair history and make them visible in a form useful for maintenance planning.

Coat Systemizer We support process design including coating and repair of outdoor and factory equipment, and improvements that consider the working environment and safety.

Summary

Coating films have a service life.

Even when the finish looks attractive immediately after application, the coating film gradually deteriorates in its service environment.

Gloss loss.
Fading.
Chalking.
Cracking.
Blistering.
Delamination.
Rust.

These are signs of deterioration from the coating film.

Waiting until deterioration has advanced and substrate protection is lost increases the repair area and cost.

This is why early detection of coating film deterioration and repair or recoating as needed are important.

Recoating does more than restore appearance.
It is preventive maintenance to protect the substrate and extend the life of equipment and products.

Coating the Future with Science and Care
CoatureVietnam supports customers’ coating quality from initial application through deterioration in service, inspection, repair, and recoating.