The board of school trustees shall have the care of the building and grounds, the school apparatus and other school property, and shall keep the county board of education advised about matters affecting the educational interest of said school. It shall attend to all incidental repairs and pay for same out of the incidental funds collected in accordance with this chapter; provided, that when repairs are to be paid for out of other than incidental funds, the amount to be expended shall be approved by the county superintendent of education and authorized by the county board of education before the repairs are made.