All public construction, the estimated cost of which exceeds ten thousand dollars, shall be let by contract to the lowest responsible bidder; all other public construction shall be let as the council may direct. If the estimated cost of any public construction exceeds five thousand dollars, but is not greater than ten thousand dollars, the board of public works shall give a Class 1 notice, under Chapter 985 of State Statutes, of the proposed construction before the contract for the construction is executed. The council may also by a vote of three-fourths of all members elected provide by ordinance that any class of public construction or any part thereof may be done directly by the city without submitting the same for bid. Unless otherwise specifically provided by action of the Common Council, all public work of the following classes may hereinafter be done and performed by the city without submitting the same for bids: street reconstruction; improvement and repair; snow removal; sewer construction; construction and laying of water mains and water facilities; improvement and repair of public buildings; construction, improvement and repair of culverts and bridges; sign and street marker painting; erection, construction and repair of street lighting. The mechanics of all other purchasing should be as directed in Charter Ordinance 6 and be under the supervision of the Finance Director.