After the filing of said certificate said commissioners of such diking district shall proceed at once in the construction of said improvements, and in carrying on said construction or any extension thereof they shall have full charge and management thereof, and shall have the power to employ such assistance as they may deem necessary, and purchase all material that may be necessary in the construction and carrying on of the work of said improvement, and shall have power to let the whole or any portion of said work to any responsible contractor, and shall in such case enter into all necessary agreements with such contractor that may be necessary in the premises: PROVIDED, That in case the whole or any portion of said improvement is let to any contractor, said commissioners shall require such contractor to give a bond in double the amount of the contract price of the whole or of such portion of said work covered by such contract, with two or more good and sufficient sureties to be approved by the board of commissioners of said diking district and running to said district as obligee therein, conditioned for the faithful and accurate performance of said contract by said contractor, his or her executors, administrators, or assigns, according to the terms and conditions of said agreement, and shall cause said contractor to enter into a further and additional bond in the same amount, with two or more good and sufficient sureties to be approved by said board of commissioners of said diking district in the name of said district as obligee therein, conditioned that said contractor, his or her executors, administrators, or assigns, or subcontractor, his or her executors, administrators, or assigns, shall perform the whole or any portion of said work under contract of said original contractor; shall pay or cause to be paid all just claims of all persons performing labor or rendering services in the construction of said work, or furnishing materials, merchandise, or provisions of any kind or character used by said contractor or subcontractor, or any employee thereof in the construction of said improvement: PROVIDED FURTHER, That no sureties on said last mentioned bond shall be liable thereon unless the persons or corporations performing said labor and furnishing said materials, goods, wares, merchandise, and provisions, shall, within ninety days after the completion of such improvement, file their claim, duly verified, that the amount is just and due and remains unpaid, with the commissioners of said diking district.