Decay of the restoration render mortar of the church of San Manuel and San Benito, Madrid, Spain: Results from optical and electron microscopy

The main aim of this research is to determine the reasons for the detachment of a mortar rendering applied to the stone masonry of the Church of San Manuel and San Benito (1903–1910), Madrid, Spain. Two building materials were analysed using optical and electron microscopy: the original limestone dressing affected by intense flaking, and the restoration render mortar used in a relatively recent rehabilitation to ‘consolidate’ the decayed stone. Results obtained by microscopic techniques and from analysis of the environmental conditions to which the building is exposed made it possible to conclude that 1) the mortar is a good material and compatible with the stone, 2) the render mortar failure was mainly due to its incorrect application and the unsuitable repair technique chosen, and last, 3) the material decay was worsened by the adverse exposure conditions of the upper section of the building (pounding rain and sunʹs radiation).