Consolidation process

The mosaic is put in place by sinking 2/3 tiles in lime. It maintains a very robust surface because the tiles are made of glass or stone for the most part. Stability is due to the plaster underneath, which is not so strong, and the wall itself. In fact, if the walls should cave in, they would make the plaster even fall apart, plaster is also by nature subject to separation and detachment, especially when it is not protected against humidity. Before proceeding to the restoration of a mosaic, its solidity must be taken into account in order to start the consolidation process.

Here at the Nativity, works had been done several years ago but with the utmost care, and in order to give more consistency to the support they had used a stronger plaster by mixing lime with different types of sand and fibers. Despite these preventive measures, time, water infiltrations, some structural failure and the weight of the mosaic itself created a massive deterioration so that we think that of the 2000 square meter of the original mosaic, only 140 remain today.

Deterioration was massive and the Piacenti Company, before starting the restoration process, had to first consolidate the mosaic.
The first step is to realize what remained solid and what underwent detachment. It is much easier to spot it on the sides but nota is easy at the centre, as the surface often appears united while underneath the tiles, the mosaic is detached from the wall: it could easily fall apart all of a sudden. For this reason, a protection bandage is applied to the walls that could present this issue.
Thanks to electronic, but also to experience, by touching it with the hands, like the doctor with the patient’s back, restorers can understand if underneath there could be some detachment. There are many types of interventions according to the situation and issue. If it is minor, liquid ethyl water is injected. If we talk about some millimetres, a semi-liquid lime is prepared.

In order to inject these, a small hole with a hand drill is made so that it does not vibrate and the restorer can immediately understand when the surface has been pierced. At this point, syringes are used like with intravenous feeding. The syringe with ethyl water remain in place until the wall continues to receive it. With semi-liquid lime an injection is made, starting from the bottom towards the top, so that all the holes are filled.
On the sides the intervention is often more drastic, because the detachment between mosaic and the wall is generally more relevant. Now we are looking at Giuseppe who is touching the cavity between the mosaic and the wall. In these cases, consolidation is more prominent: a carbon fiber net is inserted, then solid lime is applied and then the mosaic is pushed from the outside into the lime to put it back in place. All of this is carried out with the utmost care, as anything could cause a complete dissolution. The layer of lime must remain in place at least until the consolidation phase, that-is-to say after twenty days.

We see the mosaic becoming more solid in every part day by day; the most affected areas now have better conditions. Then the rest of the work becomes better: there is more serenity and no more fear of catastrophic events. Consolidation work is not over yet. In fact, procedures use major gaps to insert carbon pivots which will attach the mosaic even deeper on the wall itself.

Now we can witness this type of intervention. We are on the gap on Peter’s face, on the right transept, which portraits the entrance of Jesus in Jerusalem. Everything is ready. Restorers dust in order to see better, and now the electric drill makes a deep hole for better fastening. Matteo is working so that the hole is perfect. The hole is continuously cleaned from the dust. When the hole is perfect, Silvio puts a bandage sank in resin on the carbon bar. Then he quick inserts the bar inside the hole to reach the correct depth: in a few seconds it is done. On the outside remains the top of the pivot, in order to ensure continuity with the lime and fibers, which will fill the gap and will constitute a solid support for the whole mosaic.