Testing Wear Resistant Coatings – Challenges and Updates to ASTM D4060

An interview with Alan Jaenecke, Technical contact for ASTM D4060, VP Marketing Taber Industries and Greg Martin, Sr. Technical Advisor – Tremco Inc. CS&W

Please give an overview of ASTM D4060 and its applications.

ASTM D4060 Standard Test Method for Abrasion Resistance of Organic Coatings by the Taber Abraser is among the most common tests to evaluate the abrasion resistance of coatings. Referred to as the “Taber Test”, this test method determines the resistance to abrasion for organic coatings such as paints, lacquers, varnishes, powder coating, and many other types of finishes. In addition to the visual aspect of the coating, it often provides a functional purpose (such as protection from corrosion) too. This test method has been useful in evaluating durability and performance of coatings.  

How is ASTM D4060 testing performed?

To perform ASTM D4060, the “organic coating is applied at uniform thickness to a plane, rigid panel and, after curing, the surface is abraded using rotary rubbing action under controlled conditions of pressure and abrasive action. The test specimen, mounted on a turntable platform, turns on a vertical axis, against the sliding rotation of two abrading wheels. One abrading wheel rubs the specimen outward toward the periphery and the other, inward toward the center. The resulting abrasion marks form a pattern of crossed arcs over an area of approximately 30 cm².”[1] A vacuum system removes any loose debris generated during testing. Before each test and after every 500 cycles, the abrading wheels are resurfaced with an S-11 refacing disc to standardize the wheel surfaces. Abrasion resistance is calculated as loss in weight at a specified number of abrasion cycles, as loss in weight per cycle, or as number of cycles required to remove a unit amount of coating thickness.

What difficulties have been demonstrated when testing wear resistance in line with ASTM D4060?

The durability of protective coatings is an important consideration for many different products. It is especially important when selecting a coating that will be subjected to vehicular or pedestrian traffic such as parking garages, loading docks, walkways, etc.

To assist in this selection process, architects / consultants rely on test data – specifically the coatings resistance to abrasion. This information is typically reported by the coating manufacturer and is based on testing performed in accordance with ASTM D4060. Until recently, this long-established test method may have been misleading decision makers when comparing dissimilar coating technologies such as urethane, methyl-methacrylate (MMA), polymethyl-methacrylate (PMMA), polyurethane-methacrylate (PUMA), or epoxies.

Data presented in ASTM D4060 Precision & Bias (table 1)¹ indicates the epoxies that were tested had more than double the mass loss compared to urethane.

In over 200 project comparisons, the Taber test confirmed that epoxies and methyl-methacrylates (MMA) show high mass loss with the CS-17 abrasive wheel while polyurethane coatings had the least amount of mass loss. By itself, this data seems to imply that urethanes offer the best wear resistance. Yet in field applications, epoxies and MMA are proving to be more durable than 99% of the urethanes placed on parking decks and other trafficable services. In fact, epoxies, MMA, PMMA and PUMA last twice as long under traffic on parking decks.

Why is the wear testing inline with ASTM D4060 not providing adequate testing in this case?

Coating manufacturer’s data sheets typically present the test results as mass loss resulting from abrasion or as a wear index (reported as mass loss per cycle). However, when comparing two coatings, this data may not tell the complete story.

As an example, consider a test on two completely different materials – lead nickel composite plate and basic urethane protective coating. After subjecting both specimens to the same test conditions and number of abrasion cycles, the lead nickel composite plate shows a mass loss of 800 mg. In comparison, the urethane coating only has a 33 mg mass loss. Based on this information, it is easy to conclude the urethane coating had less mass loss and therefore would be more wear resistant. But is that actually the case?

What if you also knew the change in thickness of the lead plate was 0.1 mil compared to a 2.0 mil change in thickness for the urethane coating? Based on this additional information, you quickly realize more material was removed from the urethane specimen which implies it is actually less abrasion resistant!

For many trafficable coatings, it is important to recognize that coatings with dense filler normally show a greater mass loss compared to similar coatings without the filler, but thickness loss caused by abrasion is lower in some cases. Results for ASTM D4060 are normally reported as mass loss. But dividing the mass loss by specific gravity provides a much better relationship for the comparison.

What testing was completed to investigate abrasion considering this new information?

Tremco Inc. CS&W performed a single lab study which was started in November 2018 and evaluated over 1000 test specimens including different formulations of urethanes; epoxies; MMA; and traffic paints. All specimens were tested in accordance with ASTM D4060, but additional parameters were included to help calculate the researchers estimate of the coating’s service life.

What other factors were found to affect the wear testing in line with ASTM D4060?

Wear debris that includes extremely dense particulates may cause three-body abrasion that contributes to the break-down of the coating if not removed by the vacuum suction system. During the study, it was observed that certain abrasive wheels increase the number of wear particles that occur during the test which further contributes to the rate of abrasion.

Surface temperature increases of the test specimen were also observed when fillers such 3 dimensional crystalline structures or metallics are included in the coating. Under slow microscopic thermal video, the epoxy in contact with the CS-17 (or CS-10) wheels produce heat which binds fine epoxy particles, which the vacuum does not remove quickly enough from the abrasive wheels intimate contact with the specimen.

Other parameters were also found to influence the rate of abrasion and in many cases the coating caused greater wear of the Taber wheel. Some epoxies and MMA materials that have a hardness value or coefficient of friction greater than the abrasive wheels may cause the abrasive wheel to break down faster, especially when the coating formulation includes filler or aggregate such as silica, metal oxides or other extremely dense particulates. This “counter-attack” is impacted by particle size, count and type of particulate.

The coefficient of friction (COF) between a coating and abrasive wheel can also influence the outcome. In some tests, it was observed the COF would rise or fall between the friction source (CS-10 or CS-17 abrasive wheels) as soon as the wheel broke the surface tension – the point at which the wheel has removed the shine and is abrading the interior of the coating.

Some coatings have air entrainment bubbles that become exposed after 50 – 100 abrasion cycles which could alter the mass loss during comparison tests. For some flexible urethane coatings, the more entrained air, the less mass loss because the wheel is riding over a reduced amount of the solids content.

The interaction between wear debris with air entrainment for high reactive materials (e.g. epoxy) is significantly different. With hard epoxy coatings, the abrasion process tends to shatter the very hard particles making up the coating which causes more wear debris and higher mass loss than would be expected in service.

How will ASTM D4060 be changed with his new information?

ASTM D4060 has recently undergone a peer review and the latest release (2019) includes a note that states when comparing the wear resistance of coatings that have different specific gravities, a correction for the specific gravity of each coating shall be applied to the mass loss to give a true measure of the comparative wear resistance.

After calculating the wear index or mass loss, the result is to be divided by the coating’s specific gravity. The use of this correction factor provides a wear index or mass loss relative to the loss in volume of the material to which it is applied.

Where can readers find more information?

More information about Taber Industries can be found at www.TaberIndustries.com. For Tremco Inc., visit www.tremcoinc.com. To purchase a copy of ASTM D4060, visit http://www.astm.org/cgi-bin/resolver.cgi?D4060.

About Alan Jaenecke

Alan Jaenecke has been employed by Taber Industries since the year 2000, and plays a critical role in the company’s Materials Test and Measurement division. Although his main responsibilities include sales and marketing, Alan Jaenecke is also involved with new product development and strategic planning.

Having previously operated Taber’s in-house test facility, he has a wealth of experience conducting wear and durability tests.  He has shared his expertise in material testing with other organizations including ASTM, ISO, NEMA, Tappi, SPE, and SAE. Through industry affiliations such as ASTM and SAE, he has written new test methods and coordinated numerous reviews for existing methods.

Alan received his Masters of Business Administration from the State University of New York at Buffalo, where he earned a dual concentration in Marketing Management and Corporate Financial Management.

About Greg Martin

Greg Martin has been employed by Tremco CS & W division since 2006. Greg’s 35-year career as a protective coating and waterproofing membrane specialist, concrete mix design and structural forensics analyst has taken him to over 40 countries around the world. Greg has a degree in mathematics, structural forensics, petrographic’s and Microsoft Software Engineering. This lead the way in his development of refined software test platforms, focused test methods including enhanced petrographic analysis to protective coatings.  

Greg’s main role under Tremco CS&W, investigate and refine test methods to protective coatings, enhance or alter building code and specification verbiage based on the refined test method, concrete and coating forensics analyst.  

Greg Martin (Tremco) has been working with Alan Jaenecke (Taber Industries), to help refine ASTM D4060 in order to better reflect the abrasive performance properties of protective coatings across a wide range of formulations.

Special thanks to Ahmed Elsharawy, P.Eng., BSS., Tremco CS&W. Ahmed was responsible for Tremco’s internal ASTM D4060 Taber abrasion comparisons during the time Greg Martin took on the international cross-platform research. Ahmed has a degree in Civil Engineering and Building Science.