This study focused on the degradation processes for two historic buildings, one in a rural and one in an urban environment. Samples collected from the Romanesque Church of Torme and from two areas of the Cathedral of Burgos were studied by using optical and electron microscopy, x-ray spectrometry, x-ray diffraction, Fourier transform infrared spectroscopy and thermal analysis (TG/DTA/DTG). As result of the action of microorganisms, weddellite and whewellite were found to have formed over the entire external walls of the Church of Torme, built with dolomitic rock. Gypsum, formed by the effects of atmospheric pollution, appeared on lime plasters applied as protective coatings on the external stones of Burgos' Cathedral. Also discussed in this study is the different composition of these plasters, based on the use of calcareous and siliceous aggregates.