ASTM A933 Standard Specification for Vinyl (PVC) Coated Steel Wire and Welded Wire Fabric for Reinforcement

Get Certified ASTM A933 Testing for Reliable Coated Reinforcement Quality 

Contractors and manufacturers rely on certified ASTM A933 testing because it verifies the vinyl coating on steel wire and welded wire fabrics used to prevent corrosion in concrete, masonry, and earth reinforcement applications. The uniformity of coating thickness and adhesion are directly related to the resistance to corrosion during service life. Certified testing verifies that a batch of coated wire or fabric meets its specified coating thickness, holiday, and adhesion requirements before it is used in construction.

The scope of ASTM A933 includes: 

• Material type: Plain and deformed steel wire and plain and deformed steel welded wire fabric with vinyl (PVC) or other thermoplastic organic coating. 
• Purpose: Coating of steel wire and welded wire fabric for reinforcement. 
• Properties measured: Coating thickness, Holiday resistance, and Coating adhesion. 
• Method: Surface cleaning verification, coating thickness, holiday detection, and adhesion testing in a bending test. 
• Result: Acceptance or rejection based on coating thickness and adhesion criteria conforming to Class A or Class B. 
• Test Limitations: This test is valid for Class A and Class B minimum coating thicknesses and different end uses, and inch-pound and SI values may not be mixed. 
• Environmental conditions: Class A material qualifies for use in concrete and masonry; Class B material qualifies for use in mechanically stabilized earth applications. 
• Applications: Concrete reinforcement, masonry reinforcement, mechanically stabilized earth reinforcement, and corrosion protection of steel wire products. 

What are the Uses of the ASTM A933 Specification?

ASTM A933 testing provides a standardized method of assessing the quality of coatings on steel wire and welded wire fabric and enables engineers to verify the suitability of the reinforcement. This standard-

• Checks coating thickness of Class A reinforcement in concrete/masonry.
• Inspects thickness of coating for Class B reinforcement in mechanically stabilized earth applications.
• Supports holiday detection to locate pinholes or gaps in the protective coating.
• Assists in evaluating coating adhesion through a bending test.
• Supports manufacturers in verifying that the surface preparation has met near-white metal cleanliness.
• Collaborates in the process of inspection, rejection, and certification of coated wire products. 

What Materials Can Be Tested Under ASTM A933? 

ASTM A933 is used for plain and deformed steel wire and plain and deformed steel welded wire fabric for reinforcement. The specification is for material coated with vinyl (polyvinyl chloride or polyvinyl chloride powder compound) and also for other thermoplastic organic coatings which are equivalent in respect of the above requirements. Class A material is directed to concrete and masonry reinforcement, and Class B material is directed to mechanically stabilized earth reinforcement.

Why is ASTM A933 Important? 

The ASTM A933 testing provides a way for a manufacturer to confirm that coating thickness, holiday resistance, and adhesion are within specification, allowing for good corrosion protection throughout the service life of the reinforcement. A proper vinyl coating protects the underlying steel in steel wire and welded wire fabric used as reinforcement, which may corrode over time in the presence of moisture, soil, or aggressive environments. The specification requires the coated surface to be cleaned by abrasive blast to near-white metal, and the coating to be applied to the cleaned surface as soon as possible, before oxidation can be seen without magnification.

This specification includes standards such as ASTM A82, A185, A496, A497, A2240, A4060, G8, G12, G14, and G20.

ASTM A933 Testing Process and Data Collection

The process begins with an analyst certifying that the surface of the steel wire or welded wire fabric was cleaned to near-white metal prior to being coated. The technician then measures the thickness of the coating and compares it to the Class A or Class B specification. The operator checks for any defects in the coating using a holiday detector during the inspection. The analysts then complete the bending test to assess bonding of the coating and compare all the results with the specification’s acceptance criteria. 

Common Challenges and Troubleshooting

The accuracy of ASTM A933 results is dependent upon cleanliness of the surface, in near-white metal condition, before applying the coating, and the calibration of the thickness and holiday detection equipment. Common causes of non-conformance are inconsistent surface preparation, late coating application, and defects in the coating (pinholes). Technicians minimize these problems by checking the cleanliness of the surface just before coating and by testing each batch with calibrated equipment. Moreover, manufacturers obtain more consistent results as coatings are applied soon after cleaning and inspection is conducted in a consistent way. 

• The laboratory reports the coating thickness produced compared with the minimum thickness required for the assigned class.
• Technicians record any gaps in coating and pinholes revealed by the holiday.
• Analysts observe the bending adhesion test results and compare them with those from the tested batch.
• Engineers consider surface preparation, coating application time, and material class when interpreting the results.
• The manufacturer uses the measured coating properties to accept, reject, or certify the reinforcement product. 

Link to ASTM A933