Within 21 days after any public letting, the bidder to whom any contract shall be awarded shall enter into contract with the board of county commissioners and shall give bond to the county in a penal sum equal to the amount of the contract price, conditioned upon the faithful performance of the contract and guaranteeing the county against loss from defects of workmanship and materials. The sufficiency of the bond shall be approved by the chairperson of the board of county commissioners, but the county shall not be bound until the county attorney or county counselor approves the form as legal and binding upon both parties by the county attorney’s or county counselor’s signature endorsed thereon.