AbstractThe use of portable Raman is proposed as the modern hammer of architects to inspect protected buildings of the 20th century, where reinforced concrete was used for structures and Portland type cement for mortars/binders in the walls. Two different buildings in the province of Biscay (North of Spain) were selected, the Punta Begoña Galleries, Getxo (1918), qualified as monument, affected by a direct marine and hard industrial environment from the Bilbao Commercial Harbor, the Library of the University of the Basque Country UPV/EHU, Campus of Leioa (1968), affected by the diffuse urban‐industrial atmosphere of metropolitan Bilbao. For both cases, original and decayed compounds were searched by portable Raman spectroscopy (785‐ and 532‐nm lasers) in raw materials and efflorescence salts over them. In the Galleries, the expected raw materials of Portland‐type mortars and reinforced concrete were detected, such as alite (3CaO·SiO2), belite (2CaO·SiO2), calcite (mortar and gravel) and gypsum together with quartz and aragonite, which indicates the use of beach sand as aggregate. Other compounds like nitratine (NaNO3), nitrocalcite/niter (Ca (NO3)2.6H2O/KNO3), γ‐anhidrite (CaSO4), bassanite (CaSO4·1/2H2O), mackinawite ((Fe,Ni)S), lepidocrocite (γ‐FeO (OH)), haematite (Fe2O3) and whewellite (CaC2O4·H2O) indicated also a heavy decay, because of chemical reactions between compounds in the aerosols around the building and original materials. In the Library of the UPV/EHU, apart from the same kind of original compounds, high amounts of niter (KNO3) were detected in efflorescence just underneath the upper gardens of the building, suggesting a decay due to the infiltration of ammonium nitrate charged waters. Moreover, thenardite (Na2SO4), syngenite (K2Ca(SO4)2·H2O), gypsum (in efflorescence salts), aphthitalite (K3Na(SO4)2), haematite and anatase (TiO2) were also detected in other efflorescences.