The Silver Spring transit center was found unsafe and in need of major repairs. The $112 million bus and train hub is two years behind schedule and over budget. (Photo by Sarah L. Voisin/The Washington Post) (Sarah L. Voisin/Post)

So who lost the “weather window” needed to pour new concrete at the Silver Spring Transit Center before cold temperatures made it inadvisable?

Montgomery County General Services Director David Dise was a bit vague last week when he disclosed that the pour had been postponed until spring, effectively pushing the opening of the problem-plagued bus and train hub deeper into 2014.

But in a response to follow-up questions, Dise put the finger on designer Parsons Brinckerhoff. He said the giant international engineering firm “took a few more weeks than was hoped” to prepare plans for the two-inch overlay of latex modified concrete. Those plans had to be evaluated by county inspectors before permits were issued.

Concrete experts advised against cold weather application because lower temperatures impact drying, bonding to the underlying surface and ultimately durability.

Dise added that many things had to go right to make the weather-imposed deadline, including surface preparation and removal of drains and expansion joints. But Parsons was the source of the delay.

Parsons Brinckerhoff Regional Vice President Jerry Jannetti took issue with Dise's conclusion, calling it “an oversimplification.” He suggested that if the working group of county officials and contractors overseeing repairs hadn’t taken so much time to decide on the latex concrete as the proper fix — an idea Parsons supported for many months — the outcome might have been different. General contractor Foulger-Pratt has been outspokenly critical of the latex concrete plan.

“It took a while to get a decision on moving forward with the overlay,” Jannetti said. “Once a decision was made, we worked like crazy.”

Jannetti added that KCE, the county’s engineering consultant on the troubled project, took a month to conduct ground penetrating radar studies of the of the center to determine the thickness of the concrete at various locations.