Also, he moved from a single stage construction to an incremental two phase approach that better suited NCAR's National Science Foundation-imposed budget constraints.Despite the budgetary constraints, Pei managed to incorporate such features as bush-hammering of the concrete finish and crows nests on top of the towers that sought to meet NCAR's goal of a complex structure.[1] He used techniques such as bush-hammering the concrete, laying out geometric shapes for the buildings, and using a local pinkish aggregate to help the complex blend in with the surrounding Flatirons hills on the Table Mesa.[4] In April 1964 the Martin K. Eby Construction Company broke ground on the lab, with an estimated cost of $23.50 per square foot, well within the limit set of $25.Despite problems with leaky roofs and personnel flow, the building was considered a success in the scientific and architectural communities and, as of 2009[update], remains the primary NCAR laboratory.