Testing at five-major league baseball stadiums offers insights into paint and coatings performance
While grand architectural and aesthetic considerations for buildings may be less common than in past generations, they still matter to professional and collegiate sports stadium owners. They have important fan bases to consider. Keeping stadium structural steel looking sharp can be as important to the bottom line as providing corrosion protection. Unfortunately, stadium design, layout, fabrication, construction and maintenance all pose challenges to keeping the stadium’s steel looking its best. Undesirable color differences on structural steel members result from weathering, age and coating repairs, and touch-up painting. The good news is that faltering coatings can be readily identified, repaired and maintained. This article addresses the assessment of coating performance on the structural steel of five major-league baseball stadiums after seven to 16 years of service, with emphasis on color fade and the appearance of coating repairs. Though each stadium is unique, I’ve found their coatings, and so their appearances, tend to weather and degrade in the following common areas.
Where Steel Meets Weather
Today’s professional baseball stadiums are engineering and architectural marvels. They provide efficient access and egress and comfortably seat tens of thousands of fans. They furnish great views of their fields from every vantage point, with all the necessary support facilities from restrooms to restaurants. At least six major-league baseball stadiums feature retractable roofs to protect players and fans from foul weather.
While seating areas or enclosed concourses shelter much of the stadiums’ structural steel, many columns and trusses are exposed to weather. The same structural member often gets more sunlight on one side than the other. Columns facing the field or facing the surrounding parking, for instance, easily see more sunlight on one side, as do the upper sides of roof and escalator canopies. The steel supporting the concourse floors gets varying degrees of exposure, with the higher concourses typically getting more sunlight. Stadium gates often take the full brunt of the local climate and are generally the first stadium element that patrons see up close.
Factory Coating and Stadium Construction
Most stadium structural steel is shop-fabricated. It makes shipping easier and eliminates field-welding. However, field-bolted connections are numerous.
At most of the stadiums I’ve examined, the full coating system is also shop-applied. Shop painting is safer than field application in terms of fall protection. Surface preparation and painting is completed in an environment with controlled ambient, steel and dew point temperatures, and humidity.
One disadvantage is the amount of time between the shop-painting and actual construction of the stadium. Since the typical major-league baseball stadium has over 5,000 tons of structural steel, and can take several years for construction, the steel may be stockpiled on site or in the shop for some time.
Varying levels of exposure to weather can fade or “shift” color on certain surfaces, even before the new stadium opens. Another disadvantage is that handling, shipping and construction can damage small areas of paint. Unfortunately, touch-up coatings on damaged areas or on galvanized field-bolted connections never precisely match the somewhat weathered shop-coated steel. Spray-application versus brush and roller also contribute to non-uniformity.
Crews pressure-wash and auto-scrub seating areas, concourse floors, ramps and concession areas daily. Since many stadiums use column bents extending from the foundation through several concourse floor levels, rust at the interface of the columns and the floors is a specific concern for stadium aesthetics. Repeated washing also accelerates paint wear. Vehicles delivering concessions and conveying refuse can damage handrails and other surfaces on stadium ramps and concourses. Normal use also wears these surfaces, requiring routine touch-up paint. Again, the touch-up paint won’t precisely match the adjacent weathered paint. Assessing and Prioritizing Coating Conditions and Needs In general, the investigations subdivided each stadium into 10-15 logical areas, each of which were further divided into four to five subareas to more easily inventory the painted components. Areas and subareas generally followed stadium levels or distinct stadium components, such as ramps.
I chose subareas based on sun exposure within each level. For instance, protected spaces getting no sun were designated as different subareas than spots exposed to sunlight. The next task was determining the surface area of the steel members in each of the subareas to help develop cost opinions for repairs. These varied from about 1,000 to 50,000 square feet (93 square meters to 4,645 square meters). The following methods, standards and practices were used to evaluate the coatings and underlying substrate conditions. Visual — This assessment covered the coated surfaces for type, extent and location of coating breakdown and corrosion. The evaluation of the amount of either corrosion or coating defects, such as chipping or peeling paint, was correlated to a percentage based on the visual standard SSPC-Vis 2/ASTM D610 Evaluating Degree of Rusting on Painted Steel Surfaces. Coating Thickness — Dry film thickness was measured using a portable battery-operated digital coating thickness gage. The gage non- destructively measures non-magnetic coating thickness over ferrous substrates using magnetism. I verified gage accuracy before and after use following National Institute of Standards and Technology (NIST) thickness standards. Number of Coats — A hand-held thickness gage with a 50X microscope determined the number of coats and their thicknesses. This tool lets the investigator observe a coating cross section created by cutting through the coatings at a specific angle. The microscopic cross section reveals coating layers and thicknesses in addition to intercoat contamination, voids, underlying rust, mill scale and pinholes.
Overall Coatings Condition
Coating Adhesion — This test, conducted in accordance with ASTM D3359 Measuring Adhesion by Tape Test, Method A, involves cutting an “X” through the coating with a razor-knife, down to the substrate, then applying pressure- sensitive tape. The tape is quickly pulled from the X-cut. The amount of coating removed determines the adhesion rating, based on the standard’s rating scale. Ratings of 4A-5A represent good adhesion; 2A-3A is fair; while 0A-1A represents poor adhesion.
What the Tests Tell
The visual inspection identifies areas where corrosion is occurring, identifies other coating defects and prioritizes painting needs. The physical tests help quantify the risk of debonding when overcoating the existing painted surfaces. Table 1 defines the risk as high, moderate or low, based on adhesion and dry film thickness (DFT) findings.
High risk means the integrity of the existing coating is poor and the coating will likely detach if over-coated. Moderate risk indicates marginal integrity, but existing coatings may support additional coats. Low risk signifies that the existing coating is good and can be expected to support additional coats.
Differences in color and fading were also measured. Paint color perception is subjective and depends on several factors, including, but not limited to, the light source — sunlight vs. artificial lighting, for example; the angle of observation, gloss, surface roughness, surface dust or dirt; and surface chalking, which is the degradation of the coating’s binder from sunlight and weathering.
For objectivity, color was measured in general accordance with ASTM D2244 Calculation of Color Tolerances and Color Differences from Measured Color Coordinates (D65 illuminant, 10° observer). Color and gloss meters measured gloss in general accordance with ASTM D523 Specular Gloss. The color meter uses an integral light source and measures the color as a point in space on a three- dimensional coordinate system. Accessible areas and subareas of the stadiums’ structural steel surfaces in both sunlight and shade provided measurements. They included surface chalking to identify perceived color fading regardless of the cause. Baseline colors came from sheltered interior spaces. The field surveys determined that the condition of the coatings throughout each facility, and the level of corrosion protection afforded by the coatings, were good overall. Corrosion occurred in places typical of industrial structures. In each facility, corrosion and coating failure was most prevalent on the edges of structural steel members’ corners and on some bottom flange surfaces. Painted conduits and piping were in somewhat worse condition than the structural steel. Corrosion was more common along travel routes where deicing salts were applied or tracked in by patrons, in areas where water ponded, and where drainage systems or water supply lines leaked.
COLOR RETENTION AND FADING
Common trouble spots for corrosion and rust stains were the undersides of stairways where water and salts penetrating the concrete walking surface corroded the steel pans. Coating failure between the applied paint and galvanized substrate occurred regularly on small portions of roof decking and HVAC ductwork.
Each color measurement was an absolute value. The important factor was the difference in color between locations. The amount of color difference can be expressed as the change in one or more of the coordinates (∆L* is the change in the color on the “light to dark” or “white to black” axis). The coating industry is most often interested in change in total color represented by ∆E* and in the sum of the squares of ∆L*, ∆a* and ∆b*, the mathematical distance from two points in the coordinate system. Table 2 shows the total color change from the baseline color (∆E*) for the ballparks’ structural members. Higher ∆E* values represent greater color shift. Since most of the stadiums’ colors were dark, higher ∆E* values generally correspond to color lightening. For perspective, the amount of color change the human eye can discern is generally accepted as ∆E* equal to 3 or more for light colors and ∆E* of 2 or more for dark colors. On a typical color sample card from a paint store, the change in total color between adjacent shades from darker to lighter is ∆E* of 7, and the color change to two shades lighter is approximately ∆E* of 20. I developed an A, B and C rating scale for color change at each stadium. The ratings considered color shift, the amount of corrosion or coating defects such as peeling paint, the number of visible touch-up color differences, the gloss results and the areas of highest visibility to ballpark patrons.
|Common trouble spots for corrosion and rust stains are the undersides of stairways where water and salts penetrating the concrete walking surface corroded the steel pans.
As Table 3 shows, an “A” condition, whether “plus” or “minus,” indicates a coating in good condition with no immediate rework required. The “B” rating suggests work is needed soon. “C” indicates that significant color change has already occurred and substantial repairs should be considered. At the stadiums examined, 10-20 percent of the structural steel surfaces had an average ∆E* greater than 5 (Category C, poor condition). The majority of the stadium members had a ∆E* between 2 and 5 (Category B, fair condition). I often found members to be in good condition (Category A, ∆E* less than 2) when indoors or in well-sheltered areas. They represented 20 percent of the painted structural steel members. However, many of the stadiums’ coatings had faded relatively uniformly. Unless located directly by non-faded coatings, the uniformity of fading minimized the color shift. The field investigation and subsequent field data analysis for each stadium was used to develop coating rehabilitation recommendations, most which fell under the following general strategies.
|Table 3: Color change rating scale.
Maintenance Painting Repair Strategies
The following strategies are typical for maintaining structural steel for corrosion protection. Deferring Maintenance — Maintenance is deferred if the coatings are in good condition and there is no practical benefit to repairs; if the life of the structure is limited, making coating preservation irrelevant; or when the coatings are so deteriorated that removal and replacement is the only option. In the last instance, deferring maintenance is only viable if corrosion has not impaired the structure. If removal and replacement is the only alternative, the typical strategy is to defer it and use the money for cost-effective repair of other parts of the stadium before those coatings deteriorate to the point that removal and replacement is the only viable option for them as well. Spot Touchup — Remove all visible deposits of grease and oil from the areas of visible corrosion and deteriorated coatings in accordance with SSPC-SP 1 Solvent Cleaning. Spot power-tool clean all visible corrosion and deteriorated coatings to remove all loose rust, loose paint and loose mill scale in accordance with SSPC-SP 3 Power Tool Cleaning. Remove the existing coating in each prepared area until the periphery is sound, intact and feathered, providing a smooth transition between the coating and the substrate. After cleaning, apply all coats of the specified paint system to the prepared areas with overlap onto the surrounding intact coating. Full coats are not applied to the entire surface. The downside to this approach is that the touch-up spots stay visible. Spot Touchup and Overcoat (localized zones or entire members) — Spot power-tool clean all visible corrosion and deteriorated coatings to remove all loose rust, loose paint and loose mill scale in accordance with SSPC-SP 3. Surface preparation for recoating involves pressure-water cleaning all surfaces at 3,500-5,000 psi to remove dirt, chalk, grease, oil, loose coating, loose galvanize and other interference in accordance with SSPC-SP WJ-4 Waterjet Cleaning of Metals — Light Cleaning. Spot power-tool clean all visible corrosion and deteriorated coatings to remove all loose rust, loose paint, and loose mill scale in accordance with SSPC-SP 3. Depending on the generic type and condition of the existing coating, glossy urethane for instance, overall roughening of the surface may be necessary for proper adhesion. After cleaning, apply all coats of the specified paint system to the designated surfaces. Minimize differences by coating touch-up areas to logical break points, or by squaring off the touch up, painting 1-2 feet (0.09-0.18 square meters) from the bottom of a column and striking a straight line at that point, for example. Touchup usually poses little risk of coating failure. When applying a full overcoat to existing high-performance coatings, such as polyurethane and siloxane, an epoxy penetrating sealer followed by a coat of the same product originally applied is typically recommended. For existing acrylic coatings, additional coats of acrylic coatings are typically recommended. Coating Removal and Replacement — Remove all coatings, rust, mill scale and other foreign matter by abrasive blast cleaning in accordance with SSPC-SP 10 Near White Metal Blast Cleaning. As an alternative, if the size and location of the surface to be cleaned is not conducive to abrasive blast cleaning, you can substitute SSPC-SP 11 Power Tool Cleaning to Bare Metal. After cleaning, apply all coats of the specified paint system to all surfaces.
Scheduling Maintenance Painting
I used the A, B and C color-shift rating categories described previously as a starting point for recommended multi-year maintenance painting schedules, along with cost opinions, to complete the work for budgeting purposes. Even though the stadium owners do a fantastic job of cleaning and maintaining their facilities, it’s hard to keep up. Even the highest-performing paint is going to degrade. On what level people notice deterioration may be open to question, but people do notice. As of December, three of the five stadium owners had initiated painting work to increase their stadiums’ aesthetics, and to help create the best possible experience for their fans.
About the Author
Mike Reina is a project professional with KTA’s Engineering Surveys Department. He is a NACE-certified coatings inspector level 3, SSPC-certified protective coatings specialist and a registered professional engineer in 22 states. Reina performs project engineering, including coating and structural assessment on bridges, water tanks and other industrial structures. He provides specifications, cost estimates and blast-cleaning containment review for major bridge rehabilitation projects for state and local transportation agencies. Reina holds a B.S. in mechanical engineering from Pennsylvania State University.
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