Band 4, Heft 6

The Tower of Beiern is one of the most important monuments of Portugal. The exterior conservation of this structure was carried out in two phases: the first one serving to document the condition of the monument and assess the conservation needed and the second one to complete the actual work. The project was carried out through a three team approach: management, technical support and conservation. The fluid interaction of the three teams was the basis for the successful completion of the project. The minimum intervention principle guided the decisions that had to be taken regarding particular problems.

The Tower of Belem was constructed using the local Lioz limestone. The stone, in its "typical" variety is very compact and durable. However, different levels in the quarry produce varieties of poorer quality which can vary substantially from it. The presence of iron oxides gives rise to coloured varieties of this stone. The stone may contain many large fossils and also clay-bearing stylolites. The presence of clays in the stone makes it more susceptible to deterioration and, according to their distribution, results in different deterioration patterns. This paper describes the various deterioration patterns found on this structure and their origin. Even the most severe deterioration observed, powdering and flaking, affects mainly the immediate surface, while the stone underneath maintains its compactness.

The Tower of Beiern was colonized by various organisms, ranging from endolithic bacteria to higher plants. The paper focuses on the deterioration that the endolithic microorganisms: bacteria and cyanobacteria, algae and funghi, cause on the compact Lioz limestone. The presence of these microorganisms in the subparallel Assuring characteristic of this stone is illustrated as well as their association with the clay minerals present. Their biogeochemical action results in an increase in surface roughness, subsurface porosity and eventual flaking of the stone surface.

The cleaning of the exterior masonry of the Tower of Beiern proceeded according to schedule. It was carried out by application of water nebulization, light brushing and final rinsing by nebulized water. Areas that had more resistant stains, received extra brushing while wet and for harder crusts, such as found under corbels or recessed areas, microabrasion was used in conjunction with careful scalpel scraping where necessary. Grey areas resulting from endolithic biocolonization became evident as the cleaning progressed and given the scheduling constraints for the completion of the project, these areas received a lime-wash to give this monument visual homogeneity.

During the exterior conservation project of the Tower of Belem, Lisbon, it was noticed that although most of the Lioz limestone used in its construction was in good condition, some specific areas presented severe powdering and flaking deterioration patterns. These are mainly due to the effect of natural weathering, including anthropogenic air-pollution, on poorer quality Lioz limestone. Since the deterioration affects mainly the immediate surface and subsurface of the stone blocks, the application of stone consolidants was considered as the most appropriate solution for this problem. This paper describes the difficulties encountered in the evaluation of the tested consolidants-an ethyl silicate ester, an acrylic resin and an epoxy resin-applied in situ. The laboratory and on-site testing used in the final selection are described as well as the actual approach to consolidating the different areas that required this treatment.

The main problem presented by the Tower of Beiern masonry was the high incidence of open joints or joints with poor mortar. This situation had resulted in the infiltration of water into the Tower masonry, particularly on the Ν and W facades. After cleaning and repointing, the presence of this moisture became more evident in dampness stains, which, as the Tower dries out, are disappearing. The paper discusses the laboratory testing carried out for the selection of mortars required both for in-depth filling of joints and voids and for repointing.