A lot of Hine built Asylums were to the same layout after his pioneering design at Claybury and work done by Giles & Gough at Coney Hill; Bexley and Horton were identical as the LCC needed asylums fast, and his pattern design was used by quite a few counties who needed a new asylum quickly and cheaply.
The use of the green tiling was in fact glazed bricks; it was preferred by the lunacy commissioners because it was cheaper than applying a secondary finish and easy to keep clean.