The Liverpool Metropolitan Cathedral is the Roman Catholic Cathedral in Liverpool. It was constructed between 1962 and 1967, to the 1959 competition winning design of Sir Frederick Gibberd. The roof of the building is crowned by a tapering lantern formed from coloured glass adhered by means of an epoxy-based mortar. This construction method was experimental and at the forefront of the technology of the period. Soon after opening, the Cathedral began to exhibit flaws in detailing and construction. Leaks through the glazed lantern, between the epoxy and the glass, were observed. Therefore, the effects of outdoor exposure on the stability and strength of the used epoxy was assessed. Accelerated ageing tests allow the prediction of the effects of weathering and the state of degradation of the mortar used in the LMC in an expedited manner. Since a limited amount of original material from the cathedral is available for testing, a replica mortar was made. After a performed material analysis, the original epoxy/sand/carbon black mortar formulation was replicated. This replica mortar as well as the original mortar core samples were used to undertake accelerated ageing tests (e.g. by moisture, UV exposure and elevated temperature). This was followed by mechanical tests on the replicated specimens, to observe changes in structural integrity and adhesion. The link between the original and the replicated material was made with various chemical analysis, such as FTIR, DSC, DMA and XPS. The generated data showed evidence on that the likelihood of major structural loss is small, within the undertaken testing period. The loss of adhesion is attributed to high relative humidity. Changes in the chemical and physical properties of both materials is difficult to observe. The high filler content in the epoxy may hinder physical changes substantiality.