Products That Are Acceptable at the Factory May Rust on Site

Factory coating quality is important when coating building materials.

Has pretreatment been carried out correctly?
Is film thickness sufficient?
Is drying or baking sufficient?
Is the appearance free from debris or unevenness?
Are adhesion and corrosion protection satisfactory?

These are, of course, items that must be checked.

However, another important perspective is needed when coating building materials.

It is how the products are stored, transported, and installed after coating.

Even components coated without problems in the factory may later rust if they are exposed to rain for long periods on site, damaged during transport, or installed with unrepaired cut edges.

In such cases, the paint itself may not be the cause.
However, the result is ultimately seen as a coated product that has rusted.

Coating quality for building materials does not end within the factory.
Quality needs to be considered through storage, transport, installation, and the service environment.

Exposure to Rain After Coating Is a Major Risk

Coated building materials are transported to construction sites, but are not necessarily assembled immediately.

They may be stored on site for days, weeks, or even longer.
During that time, they may be kept outdoors and get wet in the rain.

Storage exposed to rain is a major risk even for coated components.

Particular attention is needed under the following conditions.

• Components are stacked
• Water does not drain easily
• Moisture remains inside packaging
• The coating film is damaged
• Edges and cut areas are exposed
• Water collects in bolt holes or welded areas
• The coating gets wet before it has fully cured

Brief contact with rainwater may not cause a major problem.
However, moisture remaining for a long time in gaps between components or at edges causes rust, blistering, discoloration, and peeling.

Building-material coating should not assume that post-coating storage exposed to rain is acceptable.
Even when outdoor storage is unavoidable, arrangements that avoid standing water, ventilation, protective covering methods, and storage period management are necessary.

Even Powder-Coated Products Can Rust Under Certain Conditions

Powder coating is sometimes used for building materials and light-gauge steel structures.

Powder coating uses no solvents and readily forms relatively thick films.
It can be effective for environmental performance and durability.

However, powder coating does not guarantee freedom from rust.

Even powder-coated products may rust under the following conditions.

• Insufficient pretreatment
• Insufficient film thickness
• Insufficient baking
• Thin coating at edges
• Damage after coating
• Unrepaired cut areas or drilled holes
• Moisture remaining for long periods
• Use in a salty environment
• Storage of components exposed to rain

Powder coating is an effective method, but not a universal solution.

Edges and corners in particular may have thinner films than flat surfaces.
Cutting or drilling on site also leaves those areas unprotected by the coating film.

Rather than assuming powder coating will be sufficient, manage pretreatment, film thickness, baking, edge treatment, and storage conditions together.

Rust Commonly Starts at Edges, Cut Areas, and Around Holes

Rust on building materials often begins at vulnerable areas rather than flat surfaces.

Typical vulnerable locations are as follows.

• Edges
• Corners
• Cut edges
• Drilled holes
• Around bolts
• Welded areas
• Bent areas
• Scratched areas
• Areas where water tends to collect

These are locations where the coating tends to be thin or where subsequent processing exposes the substrate.

For example, if a component is cut on site after factory coating, its cut surface has no coating protection.
Drilling also creates vulnerable areas inside and around holes.

Installing without repairing these areas allows rust to begin there.

Building materials require rules for subsequent processing and on-site repair, as well as for the coating process.

Foundation Moisture Can Cause Rust or Blistering

Building materials may contact concrete or mortar foundations after installation.

If substantial moisture remains in the foundation, it may affect the coating film or metal components.

Particular attention is needed under the following conditions.

• Concrete has not dried sufficiently
• Moisture remains where it contacts the component
• Ventilation is poor
• The structure does not allow water to drain easily
• The coating film has scratches or thin areas
• Corrosion protection specifications are insufficient

Moisture remaining for long periods makes metal components more likely to rust.
Moisture may also enter beneath the coating film or through edges, causing blistering and peeling.

These problems are not apparent immediately after coating.
They appear some time after installation.

That is why building-material coating needs to consider the environment after installation.

Plan for Salt Exposure in Coastal Areas

Salt damage requires attention when building materials are used in coastal areas.

Salt damage is the phenomenon in which salts accelerate metal corrosion.

In Vietnam, salt damage risks need to be considered in Da Nang, Hai Phong, port areas around Ho Chi Minh City, and coastal factories and buildings.

Wind and rain deposit salts on component surfaces.
Added humidity or moisture then accelerates corrosion.

The following components require attention in coastal areas.

• Outdoor steel structures
• Aluminum window frames
• Metal handrails
• Exterior panels
• Roofing materials
• Light-gauge steel structures
• Equipment support frames
• Pipe supports
• Around bolts and nuts
• Edges and cut areas

Salt-exposed environments may require greater corrosion protection than general outdoor specifications.

It is important to consider a combination of anticorrosive primers, sufficient film thickness, edge repair, weather-resistant topcoats, and periodic inspection.

Surface Treatment Also Matters for Aluminum Window Frames

Aluminum is unlikely to develop red rust like iron.

People therefore sometimes assume that aluminum is safe because it does not rust.

However, aluminum is not immune to corrosion or deterioration in appearance.
In coastal or outdoor environments in particular, it is affected by salts, moisture, ultraviolet radiation, and airborne pollutants.

Anodizing or coating may be used on aluminum window frames to improve corrosion resistance and decorative appearance.

Anodizing is a surface treatment that forms an oxide film on aluminum to improve corrosion resistance and appearance.

Combining it with coating can also provide color, decorative effects, and weather resistance.

However, surface treatment and adhesion are important when coating aluminum.
Unsuitable oil, contamination, oxide film condition, or pretreatment conditions lead to poor coating film adhesion.

Aluminum also needs pretreatment and coating specifications suited to the substrate.

Transport Damage Creates Entry Points for Corrosion

After factory coating, building materials are transported to construction sites.

The coating film may be damaged during this transport.

Examples of causes include the following.

• Contact between components
• Contact with forklifts
• Rubbing caused by load securing
• Friction with packaging materials
• Impact during loading and unloading
• Damage during temporary staging on site

Shallow coating scratches may be missed at shipment.
However, if a scratch reaches the metal substrate, rust may begin there.

Even small scratches become starting points for corrosion, particularly on components used outdoors or in coastal areas.

Preventing transport damage and checking for scratches on arrival at the site are therefore important for building materials.
Where necessary, it is advisable to prepare on-site repair paint and repair procedures.

Without On-Site Repair Rules, Quality Varies

Building materials may require on-site repair.

Damage during transport.
Damage during installation.
Cut areas.
Drilled holes.
Bolted joints.
Welded areas.
Areas exposed after assembly.

Leaving these unrepaired may cause later rust or peeling.

However, unclear on-site repair rules cause quality to vary between operators.

Problems such as the following occur.

• Insufficient cleaning before repair
• Coating while rust or oil remains
• Use of paint other than that specified
• Insufficient film thickness
• Failure to observe drying time
• Color mismatch
• An excessively small repair area
• No inspection after repair

On-site repair may look simple, but has a major effect on long-term quality.

Building-material coating needs to treat factory coating and on-site repair as a single quality management system rather than separate activities.

Include Post-Coating Storage Rules in the Specifications

Storage methods should be considered part of the specifications for building-material coating.

Defining paint, film thickness, and pretreatment alone cannot protect quality if storage conditions are poor.

It is effective to define the following storage rules.

• Use indoor storage as the standard
• Provide protective covering for outdoor storage
• Do not place components directly on the ground
• Orient components so water does not collect
• Prevent contact between components
• Ensure ventilation
• Prevent condensation inside packaging
• Control long-term storage periods
• Repair any damage
• Check appearance and damage before installation

Without storage rules, decisions are left to each site.
As a result, even identical coated products differ in quality according to storage conditions.

To protect building-material coating quality, it is important to define rules for storage, transport, and installation as well.

Storage and Installation Risks Requiring Particular Attention in Vietnam

The following risks are particularly relevant to building-material storage and installation in Vietnam.

• Long-term outdoor storage during the rainy season
• Condensation in hot, humid conditions
• Dust on construction sites
• Moisture from the ground
• Stacking components
• Salts in coastal areas
• Road vibration during transport
• Unrepaired cutting or drilling on site
• Inconsistent repair paints
• Insufficient training of site workers

These cannot be prevented solely by control within the coating process.

CoatureVietnam needs to communicate to customers that management must include storage, installation, and repair, as well as coating specifications.

The 4M Perspectives CoatureVietnam Should Check

To prevent storage and installation problems with building materials, CoatureVietnam checks from the 4M perspectives.

Material: materials

• Whether the anticorrosive primer is appropriate
• Whether the topcoat is intended for outdoor use
• Whether the coating can withstand salt exposure
• Whether powder coating film thickness is sufficient
• Whether edge repair materials are available
• Whether on-site repair paint is specified
• Whether aluminum has appropriate pretreatment and a suitable primer

Method: methods

• Whether the storage method after coating is defined
• Whether a procedure exists for checking transport damage
• Whether repair methods for cut areas and drilled holes are defined
• Whether inspection takes place before installation
• Whether protective covering rules exist for outdoor storage
• Whether film thickness and drying conditions for on-site repair are clear

Machine: equipment

• Whether sufficient curing and storage space is available in the factory
• Whether products are shipped after drying and curing
• Whether fixtures or packaging prevent damage during transport
• Whether tools and coating equipment are available for on-site repair
• Whether film thickness gauges and inspection instruments are available

Man: people

• Whether operators understand the risks of storage exposed to rain
• Whether site workers understand the importance of edge repair
• Whether forklift operators understand the risk of coating damage
• Whether managers check storage, transport, and installation conditions
• Whether storage rules are also shared with the customer

From the Management perspective, responsibilities, repair criteria, storage rules, installation rules, and warranty conditions need to be clarified.

Questions to Ask During Customer Visits

The following questions are useful when discussing rust or blistering on building materials.

• Where are products stored after coating?
• Is storage indoors or outdoors?
• Could they be exposed to rain?
• Are components stacked?
• Does their arrangement allow water to collect?
• Does damage occur during transport?
• Is cutting or drilling performed on site?
• Are cut areas and drilled holes repaired?
• Will the product be used in a coastal area?
• Will it contact foundation moisture?
• Where does the rust begin?
• Are repair paint and repair procedures defined?

These questions identify causes that cannot be understood from the coating process alone.

Summary: Building-Material Coating Quality Continues After Products Leave the Factory

Quality management for building materials does not end when they are coated in the factory.

Post-coating storage.
Damage during transport.
Exposure to rain on the construction site.
Unrepaired cut areas or drilled holes.
Contact with foundation moisture.
Salt damage in coastal areas.

These may later cause rust, blistering, peeling, or discoloration.

Even powder-coated products can rust under certain conditions.
Even aluminum deteriorates if surface treatment or coating conditions are unsuitable.
Even products that are acceptable at the factory cannot retain quality if handled poorly on site.

Building-material coating requires considering storage, transport, installation, and repair, as well as paint, pretreatment, and film thickness.

CoatureVietnam views coating as quality design that extends until the product is used, rather than only work inside the factory.

Coating the Future with Science and Care

In practice, it supports coating management suited to Vietnam’s rainy season, high temperature and humidity, coastal environments, and actual construction site conditions.