Writing Coating Specifications
How to write a clear, enforceable protective coating specification — structure, surface preparation, system requirements, application limits, inspection hold points and common pitfalls.
Key takeaways
- A coating specification is a contract document: it defines what the contractor must do and how the owner will verify it, so every requirement should be clear, measurable and inspectable.
- Most specifications follow a three-part structure — General, Products, Execution — and in North America are often organized under CSI MasterFormat Division 09.
- Reference recognized standards for surface preparation, film thickness and testing rather than writing vague descriptions such as “clean thoroughly”.
- Most coating disputes trace back to conflicts, ambiguity or unrealistic requirements in the specification.
The specification is where a coating project is really won or lost. It turns the owner’s goals — service life, appearance, regulatory approvals, budget and schedule — into enforceable instructions for the contractor and objective criteria for the inspector. A good specification makes bids comparable and inspection straightforward. A poor one invites change orders, arguments and premature failure.
This article covers how protective coating specifications are structured and written. For selecting the coating system itself, see how to choose a coating system.
Types of specifications
| Type | What it defines | Best suited to | Main risk |
|---|---|---|---|
| Prescriptive | Exact preparation, generic or named products, DFTs and procedures | Critical service, regulated work, owners with in-house expertise | Specifier carries the risk if the prescribed system fails |
| Performance | Required outcomes, such as durability, test results or appearance | Experienced contractors and suppliers, design-build | Outcomes may be hard to verify before failure |
| Proprietary | A named product system, sometimes with approved equals | Matching existing systems, specialized products | Limits competition; “or equal” clauses can be vague |
Many real specifications blend these approaches — prescribing surface preparation and inspection while allowing a choice among qualified products that meet defined performance criteria. The trade-offs of a detailed prescriptive approach are summarized below.
Advantages
- Bids are easy to compare
- Inspection criteria are explicit
- Proven systems reduce uncertainty
Limitations
- Can lock out newer, better products
- Errors become the owner’s responsibility
- Quickly becomes outdated if not maintained
Structure of a coating specification
In North America, coating sections are commonly organized under CSI MasterFormat Division 09 (Finishes) — for example, 09 90 00 Painting and Coating or 09 96 00 High-Performance Coatings — using the familiar three-part SectionFormat. Industrial owners and international projects often use their own formats, but the content is similar.
Part 1 — General
- Scope of work, related sections and referenced standards.
- Definitions, submittals (product data sheets, SDSs, qualifications, work plans, samples).
- Quality assurance: contractor and inspector qualifications, mock-ups, pre-job conference.
- Delivery, storage, handling, environmental and safety requirements, warranty.
Part 2 — Products
- Coating system by area: primer, intermediate and finish coats, generic type, DFT range per coat and colors.
- Product approval criteria, single-source requirements, thinners and abrasives.
Part 3 — Execution
- Examination of substrates and existing coatings.
- Surface preparation, application methods and environmental limits.
- Inspection, testing, hold points, repairs, cleanup and documentation.
Key technical requirements
Surface preparation
Specify cleanliness by recognized standard — for example SSPC-SP 10/NACE No. 2 or ISO 8501-1 Sa 2½ for near-white blast cleaning — plus the surface profile range and measurement method (such as ASTM D4417), and soluble salt limits where the service warrants them. See SSPC, NACE and ISO surface preparation standards.
Coating system and film thickness
State a minimum and maximum DFT for each coat and the total system, and how it will be measured and accepted — commonly SSPC-PA 2 or ISO 19840 for steel. See dry film thickness measurement. Align thicknesses with the manufacturer’s product data sheet rather than inventing new values.
Application conditions
Define limits for air and surface temperature, relative humidity and the margin between surface temperature and dew point — commonly at least 5 °F (3 °C) — while deferring to stricter limits on the product data sheet.
Inspection and testing
List hold points (for example, after surface preparation, after each coat and before backfill or service), the tests required (adhesion per ASTM D4541, holiday testing per ASTM D5162 or NACE SP0188, cure tests) and acceptance criteria. Require a written quality control plan and daily records.
For every requirement, ask: “How will the inspector measure this, and what number makes it pass or fail?” If there is no answer, rewrite the requirement.
Writing clearly and enforceably
- Use mandatory language. “Shall” for requirements; avoid “should”, “as necessary” and “to the satisfaction of the engineer” without defined criteria.
- Cite standards precisely. Name the standard and the edition policy (current at bid date, or a specific year).
- Avoid internal conflicts. Do not repeat requirements in multiple places with different values; state an order of precedence among the specification, drawings and product data sheets.
- Define “or equal”. Give objective criteria, submittal requirements and a review deadline for substitutions.
- Be realistic. Requirements that cannot be achieved in the field — or verified — are ignored or disputed.
- Keep it current. Withdrawn standards, discontinued products and outdated regulations undermine credibility.
Copying an old specification from a different project is a common source of failure. Service environment, substrate, access, regulations and available products all change. Review every clause against the current project.
A practical writing process
- Define the service. Environment (for example, an ISO 12944 corrosivity category), substrate, temperature, chemical exposure, durability target and constraints.
- Select the system. Choose generic system types and thicknesses with manufacturer input.
- Draft the three parts. Start from a maintained master specification and edit for the project.
- Coordinate. Check consistency with drawings, other sections, product data sheets and regulatory requirements.
- Peer review. Have a coatings specialist or inspector review for clarity and inspectability.
- Clarify at the start of work. Resolve questions at the pre-job conference and document the answers.
Frequently asked questions
Should a specification name specific products?
It can, especially for critical service or to match existing systems, but naming only generic types with clear performance and qualification criteria encourages competition. Many owners list pre-qualified products for each system.
What if the specification conflicts with the product data sheet?
The specification should state an order of precedence. In practice, conflicts should be raised as questions before work begins and resolved in writing with the specifier and manufacturer.
Who should write the coating specification?
Ideally someone with coatings expertise — an engineer, coatings consultant or certified specialist — working with the owner, designer and, where appropriate, manufacturers’ technical staff.
Educational reference. Coating performance varies by formulation. Always follow the manufacturer’s product data sheet, safety data sheet and your project specification.
