The influence of pre-wetting with consolidants on the adhesion of double-layer lime based mortars

Abstract

Multilayer mortar systems have been diachronically used in historic structures. Renders and plasters were usually based on lime and presented specific characteristics (i.e. stratigraphy), while their durability was mostly attributed to the adhesion and overall performance of the mortar layers. During restoration works, the replacement or repair of successive mortar layers (i.e. renders, plasters, mural paintings’ substrates) is a common practice, whose effectiveness is closely related to the proper materials and techniques applied. In this paper, an effort was made to enhance the properties of a double-layered mortar system, based on lime and natural pozzolan. To this direction, pre-wetting of the internal layer was performed, using various organic and inorganic water-solutions (lime wash, primal, hydroground) that were further nano-modified (1.5% w/w, nano-silica). A series of specimens were manufactured and their physico-mechanical properties were tested at the age of 28 and 90 days (porosity, apparent specific gravity, water absorption coefficient, vapor permeability, dynamic modulus of elasticity, flexural and compressive strength). Additionally, bond strength by pull off and tensile bond strength were performed. From the evaluation of the results, it was concluded that the application of the proposed nano-modified solutions improved significantly the adhesion of the mortar layers. The results were encouraging, indicating that a limited, low cost and non invasive technique, could enhance their performance, during restoration works.