1790s
Construction on the President’s House began in 1792 in Washington, D.C., a new capital situated in sparsely settled region far from a major population center. The decision to place the capital on land ceded by two slave states–Virginia and Maryland–ultimately influenced the acquisition of laborers to construct its public buildings. The D.C. commissioners, charged by Congress with building the new city under the direction of the president, initially planned to import workers from Europe to meet their labor needs. However, response to recruitment was dismal and soon they turned to African Americans – slave and free – to provide the bulk of labor that built the White House, the United States Capitol, and other early government buildings.
A major concern in the construction of the new public buildings in this remote location was the acquisition of building materials, such as stone, lumber, bricks, hardware, and nails. Black quarrymen, sawyers, brickmakers, and carpenters fashioned raw materials into the products used to erect the White House. Master stonemason, Collen Williamson, trained slaves on the spot at the government’s quarry at Aquia, Virginia. There slaves quarried and cut the rough stone that was later dressed and laid by Scottish stonecutters to erect the walls of the President’s House. Sawyers listed on government payrolls, such as “Jerry”, “Jess”, “Charles”, “Len”, “Dick”, “Bill” and “Jim” undoubtedly were slaves leased from their masters. Free and slave blacks burnt bricks used to line the stone walls in temporary ricks on the President’s House grounds. Often working seven days a week during the high construction summer months alongside white workers and artisans, black laborers proved vital to the work force that created both the White House and U.S. Capitol.
http://www.whitehousehistory.org/history/white-house-timelines/african-americans-1790s-1840s.html