Operations Supervisor Glen Barentine was thrilled when crews painted 14 new surface hold position markings on the taxiways at Hot Springs Memorial Field Airport (HOT) back in January 2012. But his happy demeanor didn't last.
"Six months later, the red had turned to pink because of the sun," recalls Barentine. "Even when you looked at them in the daytime, the markings had a faded color to them."
Project: Applying & Maintaining Airfield Markings
Because the Arkansas airport wanted to solve the problem instead of simply repainting, officials opted to install preformed thermoplastic markings just 11 months later. "We're very impressed with the thermoplastic," Barentine reports. "It looks great and the color, thus far, has held up amazingly."
The disappointing experience at HOT is not as unusual as most airport operators would hope. Unusual soil or pavement conditions - and even weather - can quickly turn pavement markings that look good into a "do-over."
HOT had to dig deep into its pockets for a fix. The eight thermoplastic markings crews have already installed cost $7,000 each; and the airport is planning on installing another six, for a complete replacement of all 14 painted markings.
Personnel from Ennis-Flint, the company that provided HOT's new markings, note that although preformed thermoplastic markings cost four to five times more than painted markings, they are designed and engineered to last eight to 12 times longer. "The cost is minimal when looking at the longevity of the product," says Chris Brooks, sales director of specialized markets for Ennis-Flint.
Airports that should repaint every six months often stretch their interval to a year because of budget constraints, Brooks relates. If such airports applied preformed thermoplastic markings, they wouldn't have to go back and repaint every year, he adds.
Brooks cites the Ennis-Flint markings applied at Newark Liberty International Airport (EWR) in 2006, which are still functioning seven years later, as an example of the product's longevity. "Those markings now lasted 14 times the life of paint, because they paint twice a year," he reasons.
The performance at EWR makes Barentine optimistic about HOT's anticipated replacement interval. He figures that if EWR gets seven years' of life out of its markings, HOT's markings should last 10 years, due to milder winters and lighter traffic.
Before preformed thermoplastic markings are installed, crews first apply a sealer to the substrate surface to function as a bonding agent for the markings, explains Brooks. They then roll out a preformed marking (which includes a red background, white inscription and black trim) and apply it to the sealed pavement by heating it for 60 to 90 minutes with infrared equipment in 16-foot-wide sections.
Total closure time is from two to four hours, and traffic can resume in the area 15 minutes after application, Brooks notes.
Reflective glass beads are incorporated into the preformed thermoplastic markings, adds Barentine. "The beads are embedded throughout the material," he explains. "So as it wears away, and aircraft go across it and snow plows go across it, a new layer of beads will come up."
Fungus Among Us
Severe blue-green algae have long plagued Brooksville-Tampa Bay Regional Airport & Technology Center (BKV) in Florida. Fueled by the hot, humid Gulf Coast weather, the growth became so severe that BKV's concrete runways looked like asphalt, recalls Airport Supervisor Rob Mills.
The accumulated dirt and dark algae eventually made it tough for pilots to distinguish the airfield markings. And about three years ago, the airport decided to clean its airfield and remark the runways and taxiways, which average 5,500 takeoffs and landings each month.
"Our runways had never been cleaned in literally 70 years," notes Mills.
BKV contracted Hi-Lite Markings for the job. "We went in with 20,000-psi water pressure machines and cleaned nearly 3 million square feet of surface," reports Brad Dunn, the company's Southeast Division manager. "We got rid of all the built-up algae that made the markings very difficult to see."
After cleaning the concrete, Hi-Lite repainted all the markings using standard waterborne paint. By closing only portions of the pavement at a time, Hi-Lite allowed BKV's airfield to remain active throughout the entire six-day cleaning and remarking process. "We were very careful to be as quick as possible in the areas and have constant contact regarding live aircraft," Dunn explains. "The airport never had to disrupt their operations. And it looks like they got a brand new airfield."
According to Dunn, algae growth is a common problem at airports in the southeast, because many are former military bases with porous concrete airfields. BKV, for instance, was built in 1942 by the U.S. Army Corps of Engineers for training B-17 Flying Fortress heavy bombers.
Algae growth does not always require costly remarking, clarifies Dunn. "A lot of times, we can just come in and do the pressure washing and it restores the reflectivity, the brightness of the markings and you don't even have to paint," he explains. "And why paint when you can just clean? We can save airports a good bit of money and down time."
When remarking is necessary, cleaning the surface first is still vital, Dunn cautions. "You have to have a good bond between the paint and the surface," he explains. "If you have algae, mold or mildew, those will act as a contaminant on the surface. And your paint job is only as good as the bond between your paint and the concrete. We always say that the three most important things in painting an airfield are surface prep, surface prep and surface prep."
It's been several years since BKV's cleaning and painting, and Mills is still pleased with the results. "The paint is still holding up well," he reports. "No algae are creeping through. It took 70 years for this stuff to accumulate, and it may be another seven to 10 years before we have to have them cleaned again. We're very happy."
Rust was the culprit on runways at Naval Air Station Patuxent River (NHK), in St. Mary's County, MD. "It was really bad," recalls Airfield Manager Jim Fletcher. "It was almost like somebody came out and sprayed tar over the top of the paint - it was that dark. You would never guess that the paint was white."
NHK's problem began after a routine painting in 2002, when crews used a product with different specifications because of new environmental and performance standards. "After that, we started to see the discoloration in the white pigment," says Ken Barbour, AICUZ/RAICUZ Program Manager for the Naval District Washington. "The rust color eventually overtook the light pigment. It was more of a brown stripe than a white stripe."
Marking consultant Donna J. Speidel, president of Sightline, attributes the discoloration to an iron derivative in either the aggregate used in the asphalt or the airfield's groundwater. Speidel recommended that the markings be cleaned with water blasting and then repainted with a modified formulation of TT-P-1952E waterborne paint that resists iron and rust staining.
Fletcher reports that although some rust discoloration has returned since the project was completed in 2006, "it's not nearly as bad as we had it originally."
New discoloration is isolated to cracks in the pavement that allow the iron to seep up to the surface and stain only around the cracks, notes Speidel. She consequently counsels NHK to continue using the special waterborne paint for future marking projects. "The fact that the majority of those markings are still white is a testimony to the formula modification," Speidel explains.
Keeping airfield markings clean and free from contaminants is vital to airport safety, she emphasizes. "Airport operators become accustomed to seeing stained or contaminated markings on their airfield, and they think it has to be that way; but it doesn't," says Speidel. "We're trying to provide a short-term solution to these problems so the markings last longer than they are accustomed to."