Made up of a blend of cement, water, sand and gravel, concrete is notoriously finicky. Its performance and look depend on outside temperatures and humidity as it is mixed, poured and dried. Some additives can bolster its durability but may darken the color.

But 432 Park was supposed to be white. The group assembled in Gowanus was responsible for developing a concrete mix that was strong enough to support the weight of a nearly 1,400-foot tower and white enough to satisfy the aesthetic the design team desired.

Concerned with the cracks in the model columns, Mr. Marcus recommended adding flyash to the mix, a byproduct of coal combustion often used to make concrete more durable.

“They will not accept flyash (color is too dark),” replied Hezi Mena, an engineer who was then a senior associate at WSP, in a December 2012 email.

There were two options, Mr. Marcus replied: “Color or cracks.”

“There’s no sidewalk shed that’s going to protect you from chunks of concrete popping off a 1,400-foot building,” he said.

Anthony Ingraffea, an expert in concrete fractures and a Cornell University engineering professor emeritus who reviewed photos from the inspections of 432 Park, described some of the defects as cosmetic for now, but said others have potential to peel off the building and become “concrete hand grenades.”

“I would not sign off as a licensed engineer in the State of New York that this building will last forever,” Mr. Ingraffea said. “I would sign a document that says the Empire State Building will last. This building, I doubt it.”