Surface Preparation Standards Quality Prep = Quality Finishes

Soluble contaminants (inclusive of all visible oil, grease, dirt/soil, drawing or cutting compounds, and other soluble substances) are removed from steel using solvents, such as water/steam, emulsifying agents, mineral spirits, and other cleaning compounds. Solvent Cleaning is also used to remove oil and grease from galvanized or zinc-coated parts before these pieces are profiled and cleaned by other methods.

Loose mill scale, loose rust, loose paint, and other loose detrimental foreign matter are removed by “non-powered” hand tool methods, which include wire-brushing, scraping, chipping, and sanding. Specifications for preparing galvanized steel for powder coating also include hand tool cleaning as an acceptable method to clean the substrate before surface profiling.

Mechanical methods of surface preparation, specifically “power-assisted” tools, are used to remove loose mill scale, loose rust, loose paint, and other loose detrimental foreign matter. Power sanders, power chipping hammers, abrasive grinding wheels, and rotary, impact, or power brushing tools are all acceptable mechanical instruments to remove stratified rust, weld slag, mill scale, etc. Similar to SSPC-SP2, this standard is an accepted practice to prepare galvanized and zinc-coated parts.

In this joint SSPC/NACE standard, the end condition of a white metal blast is achieved using abrasive blast media techniques. Per the SSPC, a white metal blasted surface should be, without magnification, free of all visible oil, grease, dust, dirt, mill scale, rust, coating, oxides, corrosion products, and other foreign matter. For comprehensive purposes, “white metal” describes a surface (white or gray in appearance) that is uniformly free of all foreign matter.

Similar to SSPC-SP5/NACE 1, a white metal media-blasted surface should be, without magnification, free of all visible oil, grease, dust, dirt, mill scale, rust, coating, oxides, corrosion products, and other foreign matter. However, light shadows, slight streaks, or minor discolorations caused by rust, stains of mill scale, or stains of previously applied coating are acceptable if this contamination does not comprise more than 1/3 (33%) of each area’s defined unit (3” x 3” square).

Like previous surface preparations standards, the resulting media-blasted surface shall be free of all visible oil, grease, dirt, dust, loose mill scale, loose rust, and loose coating when viewed without magnification. However, by SP7 standards, tightly adhered mill scale, rust and coating may remain on prior to coating if the adherent cannot be removed by lifting it off with a dull putty knife. As galvanized and zinc-coated pieces may cause issues detrimental to the adhesion of powder coating, Brush-Off / Sweep Blasting is an acceptable surface preparation in the cleaning and anchor profiling of these substrates. Unless otherwise specified, this process is the typical blast standard by which Houston Powder Coaters operates.

In short, Near-White Metal Blasting provides a higher level of cleaning than Commercial Blasting (SP6), but less than White Metal Blasting (SP5). Like previous surface preparations standards, the resulting media-blasted surface shall be free of all visible oil, grease, dust, dirt, mill scale, rust, coating, oxides, corrosion products, and other foreign matter when viewed without magnification. However, by SP10 standards, light shadows, slight streaks, or minor discolorations caused by rust, stains of mill scale, or stains of previously applied coating are acceptable if this contamination does not comprise more than 5% of each area’s defined unit (3” x 3” square).

Mechanical methods of surface preparation, specifically “power-assisted” tools, are used to remove loose mill scale, loose rust, loose paint, and other loose detrimental foreign matter. Power sanders, power chipping hammers, abrasive grinding wheels, and rotary, impact, or power brushing tools are all acceptable mechanical instruments to remove stratified rust, weld slag, mill scale, etc. Slight residues of rust at the bottom of pits is acceptable if the surface was pitted to begin with. Unlike SSPC-SP3, however, this standard requires the creation or preservation of a surface profile (ensuring a minimum of 1 mil between peaks and valleys). This standard is also an accepted practice to prepare galvanized and zinc-coated parts.

Primarily used to clean carbon steel, water-jetting will not produce a profile on the metal substrate; rather, it exposes the original media-blasted surface profile. Water-jetting will remove all loose rust, loose mill scale, and loose coatings uniformly while meeting the conditions of SSPC and NACE surface preparations WJ-1, WJ-2, WJ-3, and WJ-4.

Mechanical, chemical, or thermal methods used to prepare surfaces of concrete prior to the application of bonded protective coating or lining systems.

As with a commercial blast and near-white commercial blast standards, the prepared surface must be free of all visible oil, grease, dust, dirt, mill scale, rust, coating, oxides, corrosion products, and other foreign matter when viewed without magnification. However, by SP14 standards, light shadows, slight streaks, or minor discolorations caused by rust, stains of mill scale, or stains of previously applied coating are acceptable if this contamination does not comprise more than 10% of each area’s defined unit (3” x 3” square).

Similar to SPCC-SP11, mechanical methods of surface preparation, specifically “power-assisted” tools, are used to remove loose mill scale, loose rust, loose paint, and other loose detrimental foreign matter, taking the surface to bare metal. Unlike SSPC-SP11, this standard preserves the surface profile (ensuring a minimum of 1 mil between peaks and valleys), and allows for random staining to persist on the metal substrate.

Like previous surface preparations standards, the resulting media-blasted surface shall be free of all visible oil, grease, dirt, dust, metal oxides, and other foreign matter when viewed without magnification. This standard defines the cleaning and profiling (minimum of 0.75 mils) of the substrate prior to coating.


For further explanation and a complete list of surface preparation standards, please see:

SSPC (Society of Protective Coatings) – www.sspc.org

NACE (National Association of Corrosion Engineers) – www.nace.org