Teatro Nacional de S. João (Porto, Portugal) Mortar characterisation in early 20th Century Architecture

Abstract eng:
Teatro Nacional de S. João (TNSJ) is the main theatre in the city of Porto, located in the city centre and built in 1918. TNSJ was designed by the well-known architect Marques da Silva and is presently classified as a national monument. Although the theatre walls were made in the traditional way, using large granite blocks, the architect tried to introduce the use of a new binder, cement, in slabs, stairs and external decorations. The facades of TNSJ are richly decorated with a variety of elements, from simple patterns to floral elements and faces/masks of a considerable size. These elements were built around a steel frame, using mortars that possibly incorporate a cement binder. TNSJ façade presented a high level of degradation, although it has been frequently intervened in the past. Mortars from decorative elements began to detach and fall, leading to the protection of the street below and determining the need for further intervention. It was verified that mortar carbonation and the presence of salts, associated to sea fog promoted the oxidation of the metallic elements and consequent degradation of surrounding mortars. Therefore intervention procedures will imply the removal of mortars from degraded structures, the replacement or passivation of steel frames and the replacement of mortars. This work focuses on the study of the mortars sampled from the decorative elements using techniques such as acid dissolution, XRD, XRF and optical microscopy for the determination of mortar composition and capillary water absorption and mechanical strength for the determination of mortar properties. Results determine mortar proportions, type of aggregate and binder used and mortar physical and mechanical properties. This characterization of the old mortars enables the design of new mortars for the intervention.

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