Automobile graveyards and junkyards and automotive dismantling facilities in existence in Residential-1, Residential-2, Business-1, Business-2, Rural, Conservation and Industrial Districts at the time of the adoption of this chapter are to be considered as nonconforming uses. They shall be allowed up to three years after the adoption of this chapter in which to completely screen, on any side open to view from a public street, the operation or use by a masonry wall, a uniformly painted solid board fence, or an evergreen hedge, which wall, fence or hedge, shall be minimum of six feet in height.