How does a Zinc Primer work?
Zinc rich primers are used to protect steel surfaces from corrosion. Unlike regular paints or epoxies which resist corrosion by forming an impermeable barrier between the metal and atmospheric moisture, zinc rich primers provide corrosion protection by electrical means. The zinc and the steel form a tiny electrical cathodic cell that protects the steel at the expense of the zinc. Of course the zinc primer also provides a little 'barrier' protection as well.

Why use a Zinc Primer?
Some types of zinc rich primers (inorganic - see below) are used as a stand-alone coating, but often they are top coated with a paint or epoxy (many industrial coating specifications call for a zinc primer, epoxy intermediate coat and a urethane topcoat). A zinc primer under a topcoat of epoxy or urethane paint provides a backup or secondary method of protecting the steel from corrosion. Although epoxies can, and often are, used successfully on steel surfaces without any sort of general purpose primer or zinc primer.

Organic vs. Inorganic Zinc Primers
There are two types of zinc primers, organic and inorganic. Generally inorganic primers must be spray applied. They do not have to be top coated and provide better steel protection than non-top coated organic zinc primers.

Organic zinc primers (often zinc in an epoxy) can generally be applied by brush, roller or spray. If not top coated they do not protect the steel as well as an inorganic primer, but tests show they do offer the same degree of protection if the primers are top coated.

Another type of organic zinc primer is moisture cured urethane zinc primer. Moisture cured urethane coatings are easier to apply and work with than epoxy based organic zinc primers because they do not require a catalyst.

What is an MSDS?
MSDS is an acronym for Material Safety Data Sheets. MSDS information may include instructions for the safe use and potential hazards associated with a particular material or product. An MSDS for a substance is not primarily intended for use by the general consumer, focusing instead on the hazards of working with the material in an occupational setting. In some jurisdictions the MSDS is required to state the chemical's risks, safety, and effect on the environment

What are surface preparation standards?
The basic standards for preparing substrates are a joint effort between the Society for Protective Coatings (SSPC) and the National Association of Corrosion Engineers International (NACE). The most common are described below for convenience.

SSPC-SP1 Solvent Cleaning
- Removal of all visible oil, grease, soil, drawing and cutting compounds, and other soluble contaminants from steel surfaces with solvent, vapor, cleaning compound, alkali, emulsifying agent, or steam.

SSPC-SP2 Hand Tool Cleaning
- Removes all loose mill scale, loose rust, loose paint, and other loose detrimental foreign matter by hand chipping, scraping, sanding, and wire brushing.

SSPC-SP3 Power Tool Cleaning
- Removes all loose mill scale, loose rust, loose paint, and other loose detrimental foreign matter by power wire brushing, power sanding, power grinding, power tool chipping, and power tool descaling.

SSPC-SP5 / NACE1 White Metal Blast Cleaning
- When viewed without magnification, the surface shall be free of all visible oil, grease, dust, dirt, mill scale, rust, coating, oxides, corrosion products and other foreign matter.

SSPC-SP6 / NACE3 Commercial Metal Blast Cleaning
- When viewed without magnification, the surface shall be free of all visible oil, grease, dust, dirt, mill scale, rust, coating, oxides, corrosion products and other foreign matter of at least 66-2/3% of unit area, which shall be a square 3 in. x 3 in. (9 sq. in.). Light shadows, slight streaks, or minor discolorations caused by stains of rust, stains of mill scale, or stains of previously applied coating in less than 33-1/3% of the unit area is acceptable.

SSPC-SP7 / NACE4 Brush-Off Blast Cleaning
- When viewed without magnification, the surface shall be free of all visible oil, grease, dust, dirt, loose mill scale, loose rust, and loose coating. Tightly adherent mil scale, rust, and coating may remain on the surface. Mill scale, rust, and coating are considered tightly adherent if they cannot be removed by lifting with a dull putty knife.

SSPC-SP10 / NACE2 Near-White Blast Cleaning
- When viewed without magnification, the surface shall be free of all visible oil, grease, dust, dirt, mill scale, rust, coating, oxides, corrosion products and other foreign matter of at least 95% of unit area, which shall be a square 3 in. x 3 in. (9 sq. in.).Staining shall be limited to no more than 5% of each unit area, and may consist of light shadows, slight streaks, or minor discolorations caused by stains of rust, stains of mill scale, or stains of previously applied coatings.

SSPC-SP11 Power Tool Cleaning to Bare Metal
- When viewed without magnification, the surface shall be free of all visible oil, grease, dust, dirt, mill scale, rust, coating, oxides, corrosion products and other foreign matter. Slight residue of rust and paint may be left in the lower portion of pits if the original surface is pitted. The surface profile shall not be less than 1 mil (25 microns).

SSPC-SP12 / NACE5 Surface Preparation and Cleaning of Steel and Other Hard Materials by High- and Ultra-High-Pressure Water Jetting Prior to Recoating
- This standard requires water jetting at high- or ultra-high-pressure to prepare a surface for recoating using pressure above 10,000 psi. Water jetting will not produce a profile; rather, it exposes the original abrasive-blasted surface profile. Water jetting shall be performed to meet four conditions: WJ-1, WJ-2, WJ-3, and WJ-4, and a minimum acceptable surface shall have all loose rust, loose mill scale, and loose coatings uniformly removed.

Pressure Categorization:

• Low-Pressure Water Cleaning (LP WC) - Cleaning performed at pressures less than 34 Mpa (5,000 psi)
• High-Pressure Water Cleaning (HP WC) - Cleaning performed at pressures from 34 to 70 Mpa (5,000 to 10,000 psi)
• High-Pressure Water Jetting (HP WJ) - Cleaning performed at pressures from 70 to 170 Mpa (10,000 to 25,000 psi)
• Ultra-High-Pressure Water Jetting (UHP WJ) - Cleaning performed at pressures above 170 Mpa (25,000 psi)

• WJ-1 - Surface shall be free of all previously existing visible rust, coatings, mill scale, and foreign matter and have a matte metal finish.
• WJ-2 - Surface shall be cleaned to a matte finish with at least 95% of the surface area free of all previously existing visible residues and the remaining 5% containing only randomly dispersed stains of rust, coatings, and foreign matter.
• WJ-3 - Surface shall be cleaned to a matte finish with at least two-thirds of the surface area free of all previously existing visible residues (except mill scale), and the remaining one-third containing only randomly dispersed stains of previously existing rust, coatings, and foreign matter.
• WJ-4 - Surface shall have all loose rust, loose mill scale, and loose coatings uniformly removed.

• SC-1 - Surface shall be free of all detectable levels of contaminants as determined using available field test equipment with sensitivity approximating laboratory test equipment. For purposes of this standard, contaminants are water-soluble chlorides, iron-soluble salts, and sulfates.
• SC-2 - Surface shall have less than 7 µg/cm2 chloride contaminants, less than 10 µg/cm2 of soluble ferrous ion levels, and less than 17 µg/cm2 of sulfate contaminants as verified by field or laboratory analysis using reliable reproducible test equipment.
• SC-3 - Surface shall have less than 50 µg/cm2 chloride and sulfate contaminants as verified by field or laboratory analysis using reliable reproducible test equipment.