The builders of the Probota monastery built the church walls out of fine-grained sandstone. The stone, probably quarried locally, varies from a yellowish dun colour to pale green. A coarse-grained grey mortar fills the joints with particles as big as a 1cm in diameter. The vaults overhead were built of bricks. Outside, stone buttresses support the walls.

Over the stone and brick of the church artisans spread plaster properly called rendering. Lime, brick dust, chopped hemp and a little sand went into this plaster. The dust, made from pulverized bricks, is coarse with particles of up to 5mm in diameter. This rendering recipe has led to special deterioration problems.

On façades, and in areas with rising damp, small craters have formed around these large particles. The brick particles absorb water unlike the relatively impermeable lime. This difference to weathering has exaggerated salt and frost action leading to pitted surfaces.

Earthquakes strike northern Romania frequently. The church has withstood several quakes during its 450 year-old history without considerable damage. To minimize damage of any future quakes vulnerable features were reinforced.

An extrados is the outer surface of a vault or an arch and, in this particular case, the part of the vaulted ceiling which extrudes or projects into the attic of the church. This dome is particularly vulnerable to seismic shaking. In 1988-89 the extradoses of all other vaults except the one of the chancel were capped with concrete. The casts over the extradoses were at least 20cm thick. Similarly, the tops of walls were capped with a concrete ring beam 50 cm thick.

The extradoses of the vaults capped with a concrete cast

Though done with the best intentions, these modifications could actually damage the cupolas in an earthquake. Brick work moves more flexibly than the rigid cement. This difference in movement can damage the church.

The cappings also change the relative humidity and temperature conditions. Concrete, being denser than brick, absorbs less water and has a less insulative quality. This influences the painted surfaces of the intradoses, the concave ceilings of the domes, below.

More threatening to the paintings beneath the capped extradoses is salt migration. Concrete contains many more mineral salts than stone or brick. These salts leach out of moist concrete and migrate. If salts crystallize in the rendering or under pigment layers, they destroy paintings.

Despite the threat, experts recommended against the removal of the cappings. The drilling to break up the concrete would transmit damaging vibrations into the paintings below. While an earthquake might still jeopardize the domes, restorers are counteracting the salt, humidity and temperature threats by moderating them from inside the church.

For better insulation and protection against salt migration the extradoses of the vaults of the exonarthex and the burial chamber were buried in extruded clay. The vault of the chancel was covered with polystyrene panels leaving an air space around it.

Controlling the climate became top priority. A new floor was laid down and underneath it was be installed a heating system. First, a layer of loose stone 20cm thick was spread and compacted with small gravel to obtain a level and homogenous bed. Onto this was poured a 13cm thick slab of a lime-based mortar reinforced with cocciopesto and crushed limestone.

Forming a gravel base for the new floor	The sub-floor heating system

The pipes of the heating system were embedded here. These coils of heated water keep the inside temperature between 10-12C. A gas-fired boiler, installed in a shed behind the Princely House, keeps the system circulating.

Originally a 30cm wide breather band, filled with loose gravel was left to prevent moisture from penetrating into the base of the walls, and the cross walls that have frescoes. But, after careful analysis, it was decided that the breather band should also be covered with bricks. In this way all electric cables could be embedded in the floor.

The church floor has been completed with the special bricks. These new bricks duplicate the size and shape of original bricks found beneath the chancel. The floor has also been returned to its original level which is 12cm lower than the stone floor laid in 1905-1908.

Making bricks by hand in Sighisoara, Transylvania	Letting the hand-made bricks dry	The new brick floor, based the 16th century model

Originally the doorways had stone thresholds, but only one was in place at the start of archaeological excavations, and the other ones were not found. The missing thresholds and some very worn stone steps were re-made by an old stonecutter still working by hand. On the same occasion the three internal doorways were repaired with new pieces of carved stone.

Taking into account the necessity of maintaining a stable microclimate inside the church, also the church windows were replaced. The new windowpanes have double-glazing, and the new frames are wooden, to prevent condensation on the nearby wall paintings and to better control the relative humidity inside the church.

South Façade Window

Before starting the architectural interventions on the church, a team of Japanese specialists from the Shibaura Institute of Technology, determined the structural stability of the church. They concluded that no reinforcement of the church foundation was needed.

The lantern tower of the church: the new shingle roof in construction

To house the teams of restorers and archaeologists working in Probota, the project built a guesthouse. In the spirit of the project, this guesthouse was built in the traditional manner. It features a wooden frame and earthen walls. The distinctive roof is shingled with wooden shakes and has a high ridge to shed heavy snowfalls. When the project ended, the guesthouse was turned over to the Archbishopric and has served as a guesthouse of the nunnery.

The UNESCO guesthouse near completion	The Archbishop Pimen contributing to the construction of the UNESCO guesthouse

Given the scale of the restoration project at Probota, UNESCO and the Romanian Ministry of Culture worked side-by-side. Romanian architects working for the Ministry restored the roof of the church and the fortress walls surrounding it. They replaced the modern roof covering, made of metal sheeting, with traditional wooden shingles. Picturesque pointed roofs now cover the towers of the fortress walls.

The south-eastern tower with the wooden frame for the roof