Influence of application method on the use of ammonium phosphate as preservative

This work deals with the application of the Ammonium Hydrogen Phosphate as preservative and consolidant during the restoration and consolidation intervention on a twin columns group in the east side of the Santa Maria La Nova Cloister in Monreale, UNESCO Heritage from 2016. The Superintendency for Fine Arts in Palermo prescribes the use of ammonium phosphate as the only acceptable material for the consolidation of the Cloister, so this work deals with the influence of application method and solution concentration on the results achievable with this material. Particularly as the treatment have to be done on vertical surfaces the use of a supporting material is mandatory so the focus is on the use of pure cellulose pulp or a mixture of cellulose pulp and sepiolite. The experimental work started with the artificial decay of Carrara marble samples, as the columns consist of this marble. The artificially decayed samples have been treated using different concentration, i.e. 0,5, 1, 2 and 3M of di-ammonium-hydrogen-phosphate. All the solutions have been applied by means of both pure cellulose pulp and a mixture between cellulose pulp and sepiolite in one to one ratio. The sample have been characterized before and after treatment, and before and after ageing procedure, by means of optical microscopy and Raman microscopy in order to evaluate the nature and distribution of new phases appearing on the surfaces. Finally the samples underwent accelerated wash out tests in order to verify the effectiveness of the treatment. The achieved results led to choose of the treatment to be used on the columns and these data can be used for the treatment on the whole cloister and similar cases.