No person shall place, or cause to be placed, on any paved street, sidewalk, alley or other public place of the City, any damp cement, lime, concrete or mortar, or permit the same to become damp while on any street, sidewalk, alley or public place. No person shall mix concrete, cement, lime, mortar or any similar substance on any paved street, sidewalk, alley or public place of the City, except in wooden or metallic watertight mixing beds, mortar boxes or other watertight receptacles; provided, that this section shall not apply to public work done under the direction of the City Manager. (1972 Code §18-1-28.)