The consolidation of soft limestones has since long been practiced by using various products applied by different procedures, both for laboratory conditions and as real conservation actions. However, the actual performances of these consolidants have always left doubts, mostly as regards to their long-term – and, in some situations, short-term – behaviour when used for outdoor objects. The encouraging results that have been reported for the biomineralisation process in limestones, both for laboratory conditions and in trial tests, led to test it under onsite conditions to assess the operational aspects, as well as on a conservation intervention carried out for a limestone portal in the south of Portugal. The biotechnology approach reported here resorts to the activation of carbonatogenic bacteria present in the substrate’s microbiota. In this paper, the main steps and logistics requirements for this consolidation treatment - environmental control, product transport and application conditions – are summarised, onsite test results are presented and discussed, and its application in a conservation intervention is described and commented. The onset of this new consolidation treatment led us to revisit past experiences on Portuguese heritage objects as an opportunity to discuss the practical significance and applicability of the concepts of effectiveness and compatibility in the consolidation of soft calcareous stone materials. A new conceptual and practical approach to deal with the very complex and difficult problem posed by the consolidation of real outdoor exposed and decayed objects is proposed. The discussion is based on the authors’ experience on four Portuguese monuments: the Santa Cruz church (Coimbra), the Porta Especiosa of the Old Cathedral of Coimbra, the National Palace of Queluz, and the Main Portal of the Loule church. The potential of the method and its encouraging results may represent the crossing of a new technological and practical frontier to consolidate decayed highly porous limestones.