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Stone or rendered facades of historical buildings often encounter loss of cohesion after long-term weathering. Specialist consolidating agents containing nanoparticles which can penetrate the degraded layer are used to extend the lifetime of such facades. Clay mortar prepared in the laboratory was used in the present study as a material for testing the effectiveness of several consolidating agents. Changes in porosity after treatment of the sample layers were assessed using small-angle neutron scattering, mercury intrusion porosimetry and scanning electron microscopy techniques. The scattering differed for the various samples, mainly in the medium range of scattering vector magnitudes. The cause of the scattering was ascribed to three populations of pores: large (micrometres), medium-sized (thousands of ångströms) and small (hundreds of ångströms). While the non-treated sample and the sample treated with a silicic acid ester-based product do not exhibit significant differences, the sample treated with a nano-lime suspension shows a decrease of 16% in the volume fraction of medium-sized pores. A difference was also observed in the sample treated with a di­hydrogen ammonium phosphate solution: the size of the medium pores increased while their volume fraction decreased, and a change in the large pores was observed. The modelled small pores remained unaffected by the consolidating treatment.

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