Specifications Key to Successful Coatings Projects, and Inspections

COATING SPECIFICATIONS · SURFACE PREPARATION · APPLICATION · INSPECTION · QUALITY CONTROL

A protective coating project is only as clear as the specification behind it. The specification translates performance expectations into instructions for what materials to use, how the surface should be prepared, how the coating should be applied, and how the finished work will be verified.

For steel structures, a well-written coating specification should connect the selected coating system with the actual substrate condition, exposure environment, surface preparation, application requirements, inspection criteria, and expected service performance.

1. Define the Coating Product or System

The first part of the specification identifies what coating system is required.

Some specifications identify a particular approved product or complete coating system. Others define performance characteristics and allow multiple products that satisfy the specified requirements.

Where alternatives are permitted, the specification should make clear what constitutes an acceptable substitution and who has authority to approve it.

The goal is to remove ambiguity before material arrives on the jobsite.

2. Specify the Required Surface Preparation

Surface preparation is one of the most important variables affecting protective coating performance.

The specification should define the required level of cleanliness and, where applicable, the required surface profile, treatment of edges and welds, removal of soluble contaminants, repair of defects, and other preparation requirements.

Industry surface-preparation standards provide defined levels of cleaning ranging from relatively limited cleaning methods to increasingly thorough abrasive blast cleaning.

The selected preparation level should be appropriate for the coating system, existing condition of the substrate, service environment, and performance expectations.

3. Define How the Coating Will Be Applied

Once the product and substrate requirements are established, the specification needs to define how the coating system will be applied.

Application requirements may address the number of coats, target thickness, environmental conditions, recoat windows, curing requirements, stripe coating, mixing, thinning, application method, and specialized equipment.

Some materials may require specialized pumps, plural-component equipment, heated lines, specific spray tips, or other application controls.

The specification should also address known jobsite constraints that could affect application quality, access, sequencing, or curing.

The Coating System Has to Work as a System

Protective coating systems often consist of multiple layers, such as a primer, one or more intermediate coats, and a finish coat.

Those layers must be compatible with one another and suitable for the intended service environment.

A system may use coatings from the same generic family or different compatible technologies—for example, an epoxy primer and intermediate coat beneath a polyurethane finish coat.

Compatibility should be established through the approved coating system, project specification, and manufacturer guidance rather than assumed based on generic coating type alone.

Dry Film Thickness Is a Critical Quality-Control Measurement

Dry film thickness, or DFT, is one of the most commonly measured characteristics of an applied protective coating.

Too little coating may reduce barrier protection or leave the system unable to perform as intended. Too much coating can also create problems for certain materials, including curing, cracking, solvent retention, adhesion, or recoating concerns.

The project specification should identify the required thickness for each coat or for the completed system and establish the applicable inspection and acceptance criteria.

Acceptance should be based on the governing specification and applicable measurement standard rather than a single universal percentage rule.

Inspection Turns the Specification Into Verifiable Work

Inspection is an integral part of coating quality control because many important project conditions cannot be reconstructed after the work is complete.

Once a prepared surface is coated, it may be impossible to confirm visually whether the required level of surface preparation was actually achieved. Once another coat is applied, defects in the previous layer may be concealed.

Inspection therefore needs to occur at the appropriate hold points throughout the project—not only after the final coat has cured.

A Clear Specification Gives the Inspector Something Objective to Inspect Against

A coating inspector does not determine project requirements independently in the field. The inspector verifies whether the work complies with the approved specification, referenced standards, coating-system requirements, and other project documents.

That makes clear specification language especially important.

If requirements are vague, contradictory, incomplete, or scattered across documents without a clear hierarchy, disputes and inconsistent interpretation become much more likely.

The Specification Should Reflect What Is Actually Achievable

A technically sophisticated specification is not necessarily a good specification if its requirements cannot realistically be achieved on the asset.

Access, geometry, existing coating condition, environmental controls, containment, shutdown windows, substrate condition, available equipment, sequencing, and other field constraints should be considered during specification development.

The goal is to establish requirements that provide the needed performance while remaining practical, measurable, and executable.

Specification, Application, and Inspection Are Interdependent

A coating system can be well designed and still fail to achieve its intended service life if the surface is inadequately prepared, environmental limits are ignored, the wrong thickness is applied, or defects are not identified during the work.

Likewise, even excellent workmanship cannot fully compensate for a poorly selected coating system or an incomplete specification.

Long-term coating performance depends on all of those pieces working together.

Source & Additional Reading

Adapted with permission from CoatingsPro Magazine. Original article authored by R. Prasanna, Deputy General Manager — QMS, Essar Projects (India), Ltd.