The church of Saint Donatus in the Croatian city of Zadar and the Zagreb Cathedral were both recently restored, with Cortec supplying its MCI technology to prevent corrosion. In addition to the other restoration techniques employed, the corrosion inhibitor will significantly extend the life of these ancient structures.

St Donatus Image

The church of Saint Donatus is a protected cultural heritage site listed in the Register of the Republic of Croatia on UNESCO's list. Due to its unusual cylindrical appearance, it is considered one of the most significant European pre-Romanesque churches. After analyses of 3D scans, the team responsible for its restoration determined that the walls of the church, the construction itself, as well as the roof, needed work.

From 1927-1930, the stability of the foundation was compromised and reinforced concrete supports were added under the roof on the south side, connecting the outer and inner rings of the church. The moisture penetrating into the medieval monument, in combination with the sea dust, had endangered the reinforced-concrete structure. Cortec’s MCI 2020 inhibitor was specified as a coating to protect this support structure against corrosion.

MCI 2020 is a surface applied corrosion inhibitor designed to migrate through even the densest concrete structures and seek out the steel reinforcement bars. Even when not in direct contact with metal, the product will migrate through concrete to provide full protection. This environmentally safe inhibitor stops further corrosion of reinforcing metals, significantly extending the service life of the structure.

Similarly, Cortec's anticorrosion protection product- CorrVerter was used in the restoration of the Zagreb Cathedral. This church is the tallest building in Croatia, attracting tourists from across the world. The cathedral’s construction dates back to 1093, with additional structures added to the main one over the centuries. Since low-quality stone was used in the past due to economic reasons, it soon started to deteriorate, affected by weather and city pollution.

A committee was created for the reconstruction of the cathedral, selecting the Cortec product for its famous towers at the recommendation of the Faculty of Mechanical Engineering and Naval Architecture in Zagreb. During reconstruction work on the south tower, damaged steel bands were detected surrounding the tower approximately every 3m in height. They were covered with rust and in drainage areas. Damage to the diameter of the bands was easily seen.

An economical approach with a minimum of intrusion to the structure was required to fix the condition of the bands. The mechanical resistance and structural stability of the tower needed to be maintained or improved. The Faculty of Mechanical Engineering examined the bands and performed experiments on the steel bars, and recommended the removal of loose corrosion from the surface of the bands, followed by the application of CorrVerter.

This water-based primer quickly converts rust into a protective layer and is capable of penetrating into the depths of corroded surfaces. It contains a chemical chelating agent that modifies surface rust into a hydrophobic passive layer. Two-layers of CorrVerter coating were brushed onto smaller surfaces and sprayed in larger areas directly onto the metal bands. The bands were then reinforced with steel fishplates that were welded on the bands and also protected with CorrVerter.


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