4. Conclusions
Four absorbent mortars were designed in this study and used as sacrificial desalinating media. The mortars designed comprised lime, sepiolite, nanosilica (72/3/25 by weight) and three admixtures (H2O2 and two commercial aerators). The liquid/solid ratio was 0.9, porosity 40% and the mean pore size 0.8–0.7 lm. These mortars were applied three times to ashlars on a church wall affected by salts and their desalinating efficacy by number of applications was studied at depths of 0.5 cm, 1.5 cm and 3.0 cm from the surface.
When laid to a thickness of 2 cm, the mortars bonded well to the substrate for 10 days but loosely enough to be removed by hand, leaving scantly any trace on the wall.
All the mortars mobilised and absorbed soluble salts in the ashlars, eliminating ions with a small ionic volume and high mobility, especially chlorides and nitrates, more effectively. Sulfates, with a larger ionic volume, were also mobilised to the ashlar surface from the deepest depth studied, thereby raising the surface concentration of these salts. However, the anions mobilised were not fully eliminated after the third cycle of applications of the desalinating mortars.
As a rule, the mortars were more effective when the salt concentration in the wall was high and superficial. Inasmuch as nitrates and chlorides were most effectively eliminated after the first application, the suitability or otherwise of a second would need to be explored. A third application was necessary to eliminate sulfates, for the sulfate content from inside the wall rose at first. Three years after the last application, the salt concentration was just half of the value observed in the areas where all but one of the mortars were applied. The exception was the area treated with admixture-free mortar M14, where the before and after salt content were similar.
