West Crystallising House (Building 18) At Former Marsh Gunpowder Works, Workshop Area

The West Crystallising House, also known as Building 18, is a crystallising house at a saltpetre refinery that was part of the former Marsh Gunpowder Works in Faversham. It dates from between 1800 and 1810 and is currently used as a store. The building is timber framed and clad with weatherboard, with the southeast and southwest walls filled with brick nogging and a slate hipped roof.

The structure has a rectangular single-cell plan and is a single storey high. It features double doors at the southwest end and northwest side, along with three tall 5/5-pane casements on each side and one at the end.

Inside, there are three king post trusses, with the outer trusses tied to the end walls, and the floor is made of stone flags.

Historically, the Marsh works were part of the Royal Gunpowder Factory established outside Faversham in 1786 following an explosion in the town, aimed at relocating more dangerous processes. They significantly contributed to the improvement of British gunpowder during the Napoleonic Wars under William Congreve. The saltpetre refinery was built in 1789 as part of Congreve's efforts to enhance the quality of British gunpowder ingredients. The works were privatised after the war and closed in the 1920s.

The crystallising house was specifically used for crystallising saltpetre from a solution treated in the nearby refining house by cooling it in racks of vats, which is why the structure is open. It is one of two original refinery buildings on the site and is notable for its strong connection to the crystallisation process, remaining largely unaltered. This building is part of a cohesive group of late 18th to early 19th century industrial structures for refining saltpetre, recognized as the best preserved of its kind in the country, comparable to examples found in France and Sweden.