SSPC SP-5, SP-10, and SP-6: Which Surface Prep Standard Does Your Project Require?

If you have ever reviewed a coating specification or sat across from a contractor discussing a surface preparation project, you have probably encountered terms like SP-10, near-white metal blast, or commercial blast cleaning. These refer to formal standards published by SSPC - the Society for Protective Coatings, now part of AMPP (the Association for Materials Protection and Performance) - that define exactly how clean a steel surface must be before a protective coating is applied.

Understanding the difference between these standards matters more than most people realize. The surface preparation level required for a given project is not a contractor's preference or a cost-cutting decision - it is a specification requirement driven by the coating system being applied, the service environment the coated surface will face, and often the terms of a regulatory or owner compliance requirement. Specifying or accepting the wrong standard can result in premature coating failure, expensive rework, and in some cases, regulatory consequences.

This guide explains the three most commonly specified abrasive blast cleaning standards - SP-5 White Metal, SP-10 Near-White Metal, and SP-6 Commercial Blast - in plain language, with guidance on which standard your project is likely to require.

Why Surface Preparation Is the Most Important Variable in Coating Performance

The coating industry has a saying: a coating system is only as good as the surface it is applied to. Study after study of premature coating failures has confirmed that poor surface preparation - not defective coating material, not bad application technique - is the primary cause of early coating breakdown. The reason is straightforward: a protective coating can only adhere to what is actually there. If the steel beneath the coating retains rust, mill scale, grease, or other contaminants, those contaminants become the weak link. The coating may look fine on the surface while the bond between coating and steel is already failing.

This is why abrasive blast cleaning - using compressed air to propel abrasive media at high velocity against a steel surface - is the standard surface preparation method for industrial coating projects. It removes contaminants, creates a surface profile (a microscopic roughness that gives the coating something to grip), and prepares the steel for optimal adhesion. The question is not whether to blast, but how thoroughly.

Why the Numbers Are Confusing - and How to Read Them

One of the first things that trips people up about SSPC surface preparation standards is that the numbers do not follow a logical order of cleanliness. SP-5 is the highest level of cleanliness. SP-6 is lower than SP-10. SP-7 is lower than all three. The numbers were assigned chronologically - as standards were developed over time - not by cleanliness level. NACE International (now also part of AMPP) assigned its own numbering system, mapping NACE No. 1 to SP-5, NACE No. 2 to SP-10, and NACE No. 3 to SP-6. You will sometimes see specifications that list both designations together, as in SSPC-SP10 / NACE No. 2.

From highest to lowest cleanliness for abrasive blast cleaning, the order is: SP-5, SP-10, SP-6, SP-7. Keep that hierarchy in mind and the rest of the system becomes much easier to navigate.

The Four Primary Blast Cleaning Standards at a Glance

Note: The allowable staining percentages refer to randomly distributed staining from rust, mill scale, or previous coatings within each 9-square-inch unit area of surface - not visible contamination across the whole surface. In all cases, all oil, grease, dust, and dirt must be completely removed before blasting begins (per SSPC SP-1 solvent cleaning) and before the coating is applied.

SSPC SP-5: White Metal Blast Cleaning

SP-5 is the most demanding blast cleaning standard. A surface blasted to white metal must be completely free of all visible contaminants - no rust, no mill scale, no old coating, no oxides - with zero allowable staining. The result is uniformly bright, gray or white-appearing steel across 100% of the surface.

SP-5 is specified for the most demanding service environments: surfaces that will be continuously submerged, buried, or subjected to aggressive chemical contact. Think buried pipelines coated with fusion bonded epoxy, offshore platform structural steel, or submerged water intake structures. In these environments, any contamination under the coating provides a pathway for moisture and corrosive agents to undercut the coating and initiate rust - often before the coating failure is visible from the outside.

The tradeoff is production rate and cost. Achieving true white metal requires significantly more blasting time and abrasive consumption than SP-10 or SP-6, which is why SP-5 is reserved for situations where the service environment genuinely demands it. For most industrial coating projects - even aggressive ones like petroleum storage tank interior lining - SP-10 is the more commonly specified standard.

SSPC SP-10: Near-White Metal Blast Cleaning

SP-10 is the standard most commonly specified for high-performance industrial coating applications - and in our experience, the one most frequently misunderstood or downgraded without justification during value engineering discussions.

A near-white metal blast requires that at least 95% of each unit area of surface be completely free of all visible contaminants. Up to 5% of each unit area may show light staining from previous rust, mill scale, or coatings - typically appearing as faint discoloration or shadows on the otherwise clean steel. That 5% sounds like a significant allowance, but in practice it produces a surface that is visually close to white metal and provides excellent adhesion for high-performance coating systems.

SP-10 is the minimum required standard for petroleum storage tank interior lining under API 652, for secondary containment systems in chemical and petroleum environments, for immersion service coatings in water and wastewater treatment infrastructure, and for high-performance structural coatings in aggressive atmospheric environments like marine terminals, waterfront industrial facilities, and chemical plant exteriors. If your project involves any of these categories, SP-10 is the floor, not a premium option.

Important: Contractors who propose downgrading from SP-10 to SP-6 on a tank lining or immersion service project to reduce cost are not offering a value engineering alternative - they are proposing a specification change that will significantly reduce coating service life and is likely to void the coating manufacturer's warranty.

SSPC SP-6: Commercial Blast Cleaning

SP-6 is the most commonly specified standard for general industrial coating applications - structural steel in atmospheric service, maintenance painting of equipment and facility steel, exterior coatings on buildings and industrial structures in moderate environments. It is also the most frequently specified standard in commercial painting contracts, which is part of why it is called commercial blast cleaning.

A commercial blast requires that the surface be free of all visible oil, grease, dust, and dirt, with no more than 33% of any unit area showing staining from rust, mill scale, or previous coatings. In other words, at least two-thirds of every 9-square-inch unit area must be completely clean. The staining that remains must be limited to light shadows, streaks, or discoloration - not visible scale or rust.

Which Standard Does Your Project Require? A Quick Reference

The right standard for your project depends on three factors: the coating system being applied (the manufacturer specifies a minimum surface preparation requirement), the service environment (what the coated surface will be exposed to), and the project specification or owner requirement. When these three factors point to different standards, always prepare to the most stringent one specified.

One important note on coating manufacturer requirements: coating manufacturers specify a minimum surface preparation standard for each product. Applying a coating to a surface that does not meet the manufacturer's minimum requirement typically voids the product warranty and shifts liability for premature failure to the applicator or owner. If your project specification conflicts with the coating manufacturer's requirement, the conflict needs to be resolved before the project begins - not discovered after a coating failure.

A Note on Terminology: SSPC, NACE, and AMPP

You may see surface preparation standards referenced under multiple names - SSPC-SP10, NACE No. 2, or simply "near-white metal blast." SSPC (Society for Protective Coatings) and NACE International merged in 2021 to form AMPP (the Association for Materials Protection and Performance). The joint standards they published together - SSPC-SP5/NACE No. 1, SSPC-SP10/NACE No. 2, SSPC-SP6/NACE No. 3 - remain the governing specifications used throughout the industry. The content of the standards has not changed; only the organizational name has.

For most practical purposes, referencing SSPC-SP10 and NACE No. 2 are equivalent. If a specification references either designation, the same surface cleanliness requirement applies.

How Surface Preparation Is Verified - and Why That Matters

Specifying the right surface preparation standard is only half of the equation. The other half is verifying that the standard was actually achieved before the coating is applied. SSPC publishes visual reference guides (SSPC-VIS 1) with photographic comparisons showing what SP-5, SP-10, SP-6, and SP-7 surfaces look like in practice. These reference photos are used by inspectors to compare the blasted surface against the specified standard.

A NACE CIP (Coating Inspector Program) certified inspector - particularly at Level 2 or Level 3 - is trained to verify surface preparation, document surface profile (anchor profile depth, measured in mils), check for oil or moisture contamination, and confirm that the surface meets the specification before the coating is applied. On high-value or specification-sensitive projects - petroleum terminals, utility infrastructure, wastewater treatment facilities, publicly funded projects - having a NACE-certified inspector verify surface preparation before coating is applied is the single most effective way to prevent premature coating failure.

NJ Reliable Coatings has a NACE CIP Level 3 inspector on staff, available for quality assurance on every project we perform - and for third-party inspection on projects performed by others.

Working with NJ Reliable Coatings on Your Surface Preparation Project

Whether you are reviewing a coating specification, preparing for a tank entry and lining project, or trying to understand what your contractor is proposing, the surface preparation standard is one of the most consequential decisions in any industrial coating project. Getting it right protects your investment in the coating system and extends the service life of your asset.

Contact us: 908-315-4723 - or visit njreliablecoatings.com to request a project assessment and surface preparation specification review.