Work to secure Room 33, the Room of the Red Vault, has recently been completed.
An extremely rich decoration is preserved in this room, principally on the vault; in addition to the paint layers, part of the preparatory layers for the lost sectilia that originally covered the room up to a height of about 4 metres have also come to light on the walls.
Vast areas of the painted decorations are obscured by blackening due both to the deposition of carbon black and the alteration of the pigments.
Additionally, the paintings are covered to varying degrees by thick layers of calcareous concretions that have formed over time due to the constant percolation and dripping of water. As in many other rooms of the Domus, water does not just enter the Room of the Red Vault when it rains, coming in directly through the apertures – in this case a modern hole about a metre wide at the top of the vault. Even after the rain has stopped, the water that has impregnated the layer of earth above the Domus continues to filter through cracks in the wall structures and between these and the decorative layers.
Oscillations in temperature and humidity, alongside airflows that can be fairly strong, encourage the evaporation of the water present in the structure leading to the formation of salt efflorescences, carbonate layers and incrustations; these accretions, over 2 cm thick in places, show the paths of percolation.
Additionally, where the light enters, the presence of water and soil residues has encouraged the development of phenomena of bio-deterioration affecting both the decorations and the wall structures.
The survey of situations of structural risk mainly involved analysing the state of conservation of the vault to determine the presence of any obvious signs of distress. The inspection of the whole surface showed that two situations required more detailed study:
- The presence of the aforementioned hole, about one metre in diameter, in the vicinity of the apsidal wall. This hole is not only a preferential entry point for water from the garden above, but also represents a point of structural discontinuity in the vault with the risk of localized loosening and therefore of detachments.
- the presence of a vast gap in the painted decoration of the vault, indicating an extensive collapse in the past.
The first problem was tackled by postponing closure of the hole to when we decide on the system to be applied to the outside of the vaults to ensure adequate water drainage. It should be stressed that, whilst from a purely structural point of view an intervention to restore structural continuity with localized reconstruction would be ideal, the specific conditions of the monument led us to prefer closing the skylight to stabilize the microclimate without running the risk of water accumulating in the earth above after the aperture had been filled in.
The second problem was tackled by undertaking some endoscopic studies in the area of the gap in the painted decoration. This allowed us to ascertain that, despite the partial collapse in the past, the vault is still extremely thick and ensures sufficient resistance in the remaining section. Our work, as illustrated below, was thus aimed essentially at surface consolidation to avoid any future losses of the residual material still in situ.
In accordance with our usual practice, adopted for all the interventions in the Domus, we first recorded the decorations and structures and photographed them.
After erecting the scaffolding, we proceeded to record the state of conservation of the structures and the decorations, tapping the surfaces to identify any detachments.
On the basis of these preliminary diagnostic tests, we then disinfected the surfaces to eliminate the forms of bio-deterioration present; this was completed by mechanically removing the residual biological patina using cotton buds and nylon brushes.
Work then continued with the removal of an extensive cement layer applied in the modern period to close a large hole present in the decoration of the vault in the vicinity of the counter-façade wall. This layer of cement altered the permeability of the original wall structure, leading to considerable pooling and accumulation of water, compromising the conservation of the adjacent decorations.
After eliminating this harmful cement layer, we extracted the soluble salts, cleaned the surface and repaired the cohesion defects of the original wall support.
All the cohesion defects were repaired by repeatedly impregnating them with nanolime dispersed in isopropyl alcohol.
We then proceeded to repair the adhesion defects recorded in the decoration of the vault and walls, between the preparatory layers and between these and the wall structure. We used all the cracks already present to inject the consolidants, keeping the opening of new holes to the bare minimum.
Considering the number and size of the detachments found, we chose to use a product consisting of a mixture of hydraulic binders and inert powders, which have the specific property of a lower diffusion capability within the walls. This allowed us to obtain a series of points of adhesion to the wall support, sufficient to secure the decorations without overly burdening the structure with the excessive addition of consolidant.
Work was completed by plastering the lesions and cracks present using a lime-based mortar resembling the original mortars in terms of components, colour and aggregate size (granulometry).
After operations to secure the decorations, we applied a further biocide treatment to prevent bio-deterioration phenomena developing.
Work carried out by the company IMAR and the conservator Fabio Fernetti.
Collaboration on the graphic and photographic documentation Arch. Maria Rita Acetoso.