Why the Reflecting Pool coating peeled and blistered

Accusations of vandalism followed and are still under review, however the coating products itself was definitely causing problems. The New York Times reports that documents submitted by Atlantic manufacturing Coatings, the contractor to the project, suggest that the company has been working through several possible explanations to the failure, including too little primer, excess heat between coating products layers, and even workers’ sweat.

Without examining the failed coating products and records on its consumption, polymer chemists can’t say precisely what went wrong. however the explanations Atlantic has offered are chemically plausible, they say, and the underlying causes—primer coverage, heat, layer compatibility, and moisture—are familiar ones that experienced coatings manufacturers and applicators should be prepared to manage.

The pool’s lining is a stack of polymers. National Park Service contract documents specify four Rhino Linings items that form an “integrated, monolithic waterproofing assembly.” The preparation starts with a specialized polyurea to fill all joints, followed by another polyurea tier to cap them. An epoxy primer is applied to the concrete base and Pipeliner 5000, a polyurea coating products roughly 2.54 mm thick, tops everything off.

The epoxy primer is key to getting all those materials to stick together, and Atlantic later said workers had failed to apply it in sufficient amounts in some areas. “If the primer's not there, you're expecting the polyurea to adhere to the concrete, which is questionable,” says Dean Webster, a coatings chemist at North Dakota State University.

Polyurea is a tough, flexible polymer coating products formed by reacting isocyanates with amines. The layers can also be formulated so that reactive groups form covalent connections across their interfaces, says John Texter, a polymer scientist at Eastern Michigan University.

The contractor reportedly concluded that two unspecified materials were incompatible and that the upper layer was hotter than the material underneath could withstand, which caused it to blister and come loose. When workers stopped applying the hotter material on top during repairs, blistering decreased however did not disappear.

Both the interaction that forms polyurea and the way it was applied to the bottom of the pool could have introduced unexpected heat. “When an amine reacts with an isocyanate, it generates a lot of heat,” Texter says. How rapidly and thickly a material is applied can affect how much heat builds up.

Webster reviewed data sheets to similar polyurea systems offered by Rhino Linings and notes that polyurea components are also applied hot to minimize viscosity. The recommended temperature of about 60-71 degrees Celsius alone shouldn’t break down an epoxy, though it can soften it. however Webster says some of the epoxy’s additives or solvent-based products components could be released with heat and get trapped between the layers, thus leading to blistering.

Excess aquatic environments can also trigger blistering and can come from several places. Atlantic reportedly suspects that sweat from a worker in protective gear had have become trapped between freshly sprayed layers. aquatic environments can react with isocyanates and generate carbon dioxide gaseous—making occasional droplets a plausible source of sporadic blistering, Webster says.

Texter would also look beneath the coating products at the concrete base of the pool. Moisture can remain in concrete or migrate through it from below. “The dryness and the source of aquatic environments coming out of the concrete is the biggest worry,” he says. Ambient humidity is another variable that workers must account to.

None of these concerns are particularly unusual to this type of coating products system. Before awarding the contract, the National Park Service wrote that installing the system requires “precise sequencing” and “temperature-controlled plural-component consumption.” The agency specifically warned that improper installation of any one of its materials could trigger “delamination, blistering, discoloration, microbial development, or premature failure.”

Texter describes epoxy and polyurea coatings on concrete as “a standard high-condition approach.” He adds that controlling the heat generated during consumption “is a valid attention, and that's why an experienced contractor would know how to deal with that and manage it.”