Changes to potable water coatings bring applicator challenges

New standards reduce levels of solvents allowed in coatings

“Ripple effect” is a term commonly used to describe outlying consequences caused by a disturbance. When a pebble is dropped into a still body of water, the ripples transmitting outward disrupt the surface far beyond its initial impact point. For those in the coatings industry who participate in potable water projects, a small change to a single test will have far-reaching effects on which coatings technology can be used in the future.

Potable water coatings in contact with drinking water are tested and certified to NSF International/American National Standards Institute (ANSI)/National Standard of Canada (CAN) Standard 61, “Drinking Water System Components — Health Effects.” This standard covers coatings used for a variety of structures and components, including storage tanks, pipes, valves, pumps, and fittings. Besides a toxicology review of the formulation, the test for Std. 61 involves immersing coated panels in water after a predetermined cure time and then testing the water at various intervals for specific constituents that may have leached from the coating. Once the test is completed, the amount of leached compounds extracted into the water determines the size restrictions of the tank, pipe, etc. on which it can be applied.

The 2018 edition of Std. 61 included an update in response to an extensive toxicological study conducted by Health Canada, one that ultimately resulted in a modification of the Canadian regulatory criteria for solvents such as xylene, ethylbenzene, and toluene in drinking water. At the same time, the pass/fail criteria within Std. 61, previously Annex D, were moved to a new standard called NSF/ ANSI/CAN 600-2019, “Health Effects Evaluation and Criteria for Chemicals in Drinking Water” (NSF 600), which was adopted as a companion to Std. 61. The Health Canada criteria added to NSF 600 radically reduced the extractable levels of xylene, ethylbenzene, and toluene allowed in products certified to Std. 61. Although there is not a universally mandated implementation date, most testing agencies, including NSF, have announced January 1, 2023, as the date that the new pass/fail criteria for these extractable compound limits will take effect.

Extraction Criteria changes for NSF 61/60

Previous Criteria     New Criteria

Maximum Contaminant Level(mg/L)

Xyene                    10                    0.09 (total)

Toluene                  1                     0.06

Ethylbenzene         0.7                    0.14

 Challenges of NSF 600 coatings standard

What does this mean for the coatings industry and for coatings applicators specifically? The aforementioned solvents are widely used in all types of coatings, including those designed for use in potable water immersion. In practical terms, NSF 600 extraction requirements will eliminate most of the solvent-borne coatings currently certified to Std. 61 and will require the use of 100 percent solids or compliant high-solid formulas that contain alternative solvents.

One hundred percent solids epoxy and aromatic urethane linings have been on the market for years and have been successfully used in potable water applications. Performance of these coatings is very good and typically offers the owner a thicker coating film that can prolong service life. However, they do represent a challenge for applicators because of their short pot life during airless spray application and because they may require the use of plural-component (PC) equipment.

Over the years, coatings manufacturers have introduced more forgiving 100 percent solids, airless-spray-applied coatings, but pot life is still a major consideration for applicators. Most coatings of this type have a useful spray life of under 45 minutes, unlike lower-solids, solvent-borne coatings, which are typically measured in hours. Crews applying these coatings to tanks or pipes must be well organized and especially watchful of the pot life to avoid poor spray patterns and ruined hoses.

Despite these challenges, many crews have preferred these coatings due to faster, one- or two-coat applications that reduce the time on site and allow them to move on to other projects.

Spraying smaller components of a jobsite, such as pumps and valves, can be especially challenging with 100 percent solids materials because they are easily overbuilt on angles — because of their high build and edge retention — and it can be difficult to achieve uniform thickness over complex geometries.

But the good news is that application by PC is not the exotic effort it was 20 years ago. As crews have become adept at application and as equipment has improved, many applicators eagerly pursue projects with coatings applied by PC. By removing pot life concerns, the primary drawback of 100 percent solids materials is eliminated, although the same challenges with overbuilding film thickness remain for smaller components and complex geometries.

Standard impacts all aspects of potable water coatings projects

Applicators who traditionally bid projects using lower-solids materials will be pushed to invest in new airless pumps capable of 5,000 psi (34.5 MPa) or greater pressure or to the more expensive and complex PC rigs. To help eliminate these barriers, several companies offer rental services for such equipment, including on-site pump-support technicians. These services prevent the applicator from investing large sums in new spray equipment and have even proved to significantly increase crew productivity by reducing downtime due to pump repair and malfunction.

As they transition their coating specifications for compliance to the updated solvent criteria within NSF 600, engineers and specifiers will begin specifying more 100 percent solids epoxy linings and aromatic urethane linings. Meanwhile, applicators should be ready with the needed equipment and training.

However, coatings manufacturers may also find a way to salvage specific formulations, and, in some cases, this has already begun. Certain zinc-rich, moisture-cured urethane primers have achieved compliance to the updated criteria, and some higher-solid, solvent-borne epoxy linings may survive (depending on their extractable levels and end use). New formulations using alternative solvents will also likely be commercialized prior to January 1, 2023. Solvents such as methyl ethyl ketone (MEK), methyl n-amyl ketone (MAK), butanol, and even water itself could yield immersion-grade performance with the ease of use typical of lower-solid products.

Increased attention to potable water specifications needed

While engineers are focused on updating their coatings specifications, applicators should carefully review those specifications prior to a bid to make sure all aspects of the surface preparation and coatings system are consistent with the manufacturers’ instructions. Extra time spent on a thorough review and identification of small but important details could prevent headaches once the project starts.

Surface Preparation: Manufacturers will continue to require NACE No. 2/Society for Protective Coatings (SSPC) Surface Preparation (SP) 10, “Near-White Blast Cleaning,” for immersion service, but the anchor profile for direct-to-metal application of high-solids materials could change. For example, a lower-solids epoxy coating may require a 1.5-mil (38.1 microns) anchor profile while the high-build nature of 100 percent solids products could require a 3.0-mil (76.2 microns) profile. 

A popular technique among many contractors who apply high-solids coatings in water tanks is to blast the entire surface and then apply one heavy coat of the specified topcoat instead of blasting and painting one section at a time. Preserving the blasted surface in this case is vitally important and can be achieved by using an appropriate NSF Std. 61 primer and dehumidification equipment or by using an approved surface preparation additive.

Primer: Many coatings specifications will continue to include multi-coat systems incorporating an NSF Std. 61 primer. Besides additional corrosion protection, primers can be helpful during application when applied over the entire substrate to hold the surface preparation profile prior to application of the high-build topcoat. Since many primers are lower in solids and contain solvents, ensure that they are compliant to the new criteria in NSF 600 and compatible as part of the specified system.

Stripe Coat: Experienced inspectors will recognize that the earliest signs of corrosion inside a water storage vessel or component appear on weld seams and angles. Stripe coating these areas is critical to long-term substrate protection. Applicators should identify whether the coatings specification lists a product for stripe coating and then, just as with primers, make sure it is compliant to the updated criteria in NSF 600 and listed as part of the NSF Std. 61 coatings system. 

Topcoat: High-solids materials, by their very nature, tend to build quickly. This is a positive attribute when labor-saving, one- or two-coat systems are applied, but there are challenges as well, particularly with overbuilding the dry film thickness (DFT). 

The product data sheet will identify a maximum film thickness, but this may exceed what the product’s NSF Std. 61 listing allows. Double check the Std. 61 listing with the specified DFT, and resolve any inconsistencies. This is also a good time to establish agreement on the use of SSPC Paint Application Standard No. 2 (PA-2), “Procedure for Determining Conformance to Dry Coating Thickness Requirements,” in relation to acceptable areas where DFT exceeds the specified range. However, final DFT must still be compliant with the Std. 61 listing.

Another thing to consider is that many high-solids materials have very specific and limited recoat windows, which tend to be shorter than those of lower-solids, solvent-borne coatings. Pay particular attention to maximum recoat windows when tie-ins or overlaps occur.

Thinning high-solids materials, as allowed by the manufacturer, can improve application characteristics, but the ability to use additional solvent could change for NSF 600 compliance. Additionally, municipalities may have local extractable requirements unrelated to NSF 600 that can be extremely low and easily exceeded with even minimal thinning. Extra caution must be taken when thinning to avoid violating these local requirements.

Equipment: Manufacturers of 100 percent solids products have specific spray rig configurations that they recommend for optimum application. Those equipment guidelines should be obtained from the manufacturer, or the applicator’s current equipment should be reviewed and deemed appropriate for use with the specified system. Small details, such as hose diameter, may seem inconsequential, but it can have a substantial effect on things such as application productivity and spray pattern. A few minutes consulting with the manufacturer’s technical service team prior to project commencement can prevent difficult issues in the field later.

Preparing for tomorrow’s potable water coatings projects

The extraction requirements of NSF 600 will certainly send ripples throughout the water and coatings industries. For some who have already made the switch to high-solids coatings because of volatile organic compound (VOC) regulations or local extractable requirements, those ripples will be barely noticed. But for many others, the disturbance will be more pronounced. Engineers, owners, original equipment manufacturers, and certainly applicators will need to change the products they have become accustomed to over the years.

However, as this change is not immediate, there is ample time to prepare by purchasing or renting equipment, training crews, watching for new product innovations, and carefully reviewing the updated specifications that will begin flooding the industry. Properly preparing for the changes brought on by NSF 600 could be the difference between experiencing a small ripple or a tidal wave.

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Source: Originally appeared in CoatingsPro Magazine, November 2020; authored by Mark Thomas, Tnemec Company, Inc.

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