On the Possible Role of Opuntia ficus-indica Mucilage in Lime Mortar Performance in the Protection of Historical Buildings

Abstract

In Mexico, the preparation of lime mortar may include the addition of nopal juice. The lime mortar
prepared in this way has been used for centuries for restoring and protecting historical buildings
because of an improved performance against water penetration and cracking. To date, no scientific
explanation has been offered to explain the use of cactus juice in lime mortar. The objective of this
study was to provide a preliminary experimental account of the use of nopal juice as an
impermeabilization agent. Calcium hydroxide and commercial slaked-lime pastes were prepared
and mixed with varying concentrations of nopal juice at ratios of 0.65%, 1% and 1.95% of cactus
juice to Ca(OH)2 or commercial slaked lime. The dry pastes thus obtained were evaluated by a
penetration-breaking test with a TA-XT2 texture analyzer. Increasing amounts of cactus juice in the
formulation resulted in a drastic reduction of the maximum stress and deformation values of the
pastes as compared to those of the control sample. In the control sample, a more mechanically
homogeneous Ca(OH)2 structure was formed. In the sample with the lower cactus juice ratio, the
mucilage had a reduction effect upon the continuity of the network. The amorphous soft filler,
forming a discontinuous phase, makes the hydroxide network weaker. As the ratio increased,
mechanical properties also increased due to the formation of a homogeneous network of nopal
mucilage interpenetrated into the hydroxide base. Results indicate the formation of an
interpenetrated network of nopal mucilage with no structural modification involved.