Comparison between ammonium phosphate and nanolimes for render consolidation

In this study, a systematic comparison is presented between ammonium phosphate and commercial nanolimes for the conservation of lime-based renders. Such comparison is very significant, considering that nanolimes are the most widely used inorganic consolidant commonly applied onto plasters, renders and frescoes. Specimens made of slaked lime and siliceous sand were prepared, by applying the fresh mortar onto a solid brick substrate. After curing for 4 months, samples were consolidated by (i) an aqueous solution of diammonium hydrogen phosphate and (ii) commercial nanolimes. The effects of the treatments were evaluated in terms of composition and morphology of the new phases, effectiveness (ultrasounds and scotch tape test) and compatibility (color change and water absorption). The results of the study confirm the high potential of the phosphate treatment, able to provide higher mechanical consolidation in a shorter time (24 hours, instead of at least 4 weeks for nanolimes), while being equally compatible from the aesthetical and physical point of view.