Construction crews in downtown Dallas are racing to finish a 52-story jigsaw puzzle.

They are installing tons of marble that was taken down two years ago from the exterior of landmark First National Bank tower on Elm Street.

As part of the renovation of the 54-story skyscraper, contractors had to remove acres of Greek marble that had covered the tower since it opened in the mid-1960s.

Decades of wind, water and sun had left the polished stone exterior of the 1.5 million-square-foot office high-rise cracked and discolored.

The original stone panels were all removed and shipped to plants in Asia and Florida for restoration.

Getting all that stonework back on the building is critical to maintaining the tower’s historic status. It’s like putting new tile in your shower — if your shower were the size of an aircraft carrier.

When Dallas’ Todd Interests recently took over the $450 million redevelopment project, getting the marble instillation on a fast track was a top priority.

The project has to be finished by the end of next year to qualify for $100 million in historic preservation tax credits.

Steve Brown, Real Estate Editor