CONTEXT 180 : JUNE 2024 57 German, Peru, the West Indies, Italy, Egypt, Spain and Brazil, and sourced within the UK over the course of 20 years. The site deteriorated after the villa was demolished in 1808 and the shining gemstones have been subject to pilfering. In more recent times, the collection and the tunnel structure, which is open to the school and the general public on an appointment-only basis, has suffered from decay caused by water ingress, natural stone loosening and deterioration, inappropriate repairs using cement mortar, and rusting iron fixtures. The project to conserve and restore the grotto has spanned over 20 years. Many of the individuals, including the client team; Nicolette Duckham, the senior conservation officer; the Donald Insall Associates team; and the conservator team from Taylor Pearce spent several years enabling the works, implementing the conservation and alteration works over two phases. The South Chamber was selected as the pilot area (Phase 1 works). Repair works, carried out in 2017, informed the conservation methods and philosophy for the rest of the grotto. The last stage, Phase 2, was carried out in 2022 and 2023. The rendering that holds together precious and semi-precious stones to the brick substrate was consolidated and stabilised and the stone surfaces gently cleaned. Cementitious materials were removed. The removal of the cement screed to the floor uncovered the historic brick floor and enabled the building to breathe. All minerals were conservation cleaned and physically checked to confirm that they were stable. Individual loose minerals, areas suffering from deteriorating mortar or detrimental cementitious pointing were identified. All minerals were reset using a lime-putty mortar. This included individual loose minerals and larger areas where the minerals were recorded prior to dismantling to enable them to be reset in their original position. The background mortar was taken back to a sound surface, with the surface prepared with a key and edges cut back at right angles. A slurry was applied to the background and a scratch coat layer used as required. Areas of missing minerals and inappropriate repairs were rebuilt using new minerals. This was done in the same way as the resetting of the original material, with the backgrounds thoroughly prepared and scratch coats applied where necessary to build the surface out to the surrounding area. All background material was consolidated prior to the setting of the minerals. Stainless-steel fixings were used as required for larger and projecting stones. Where possible, historic fixings were incorporated into supporting the new minerals. Stainless steel was set in either Prompt natural cement or Hilti HY-170 resin. All areas of the walls and ceilings were inspected and consolidated as required. Voids and open joints were packed out with a lime-putty mortar. Brick and tile were used in larger voids and the voids filled in layers if necessary. Loose minerals were stabilised with mortar if possible or removed for resetting. Mortars were covered and tendered for several days, before being raked and tamped to provide the required finish. Sketches by William Kent from the 1730s An Exact Draught and View of Mr Pope’s House at Twickenham (1735)
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