## 4 Global Discussion  
According to these findings, considering the physical and mechanical results, it can be observed that the mortar with slaked air lime (A), despite its chemical and physical compatibility with the ancient renders, presents relatively low strengths and a high rate of water absorption, which could be a drawback in the environmental conditions of the Fort. However, these characteristics improve with the curing age. Adding quicklime to the slaked air lime mortars (A+Q10% and A+Q30%), an increase in the mechanical strengths is observed, especially after 180 days. Furthermore, the additions of 30% of quicklime seems to have the most positive influence on the mortar performance, since there is a reduction in the capillary water absorption and the drying occurs relatively faster. Moreover, this composition presents a reduced w/b ratio that, consequently, reduces the porosity and improves the mechanical strengths in the hardened state, which are very important characteristics for the replacement mortar to be successful in this severe environment. However, after few cycles of capillary absorption/drying, black mould arises on the top of the A+Q specimens; therefore, the use of this composition in local areas with high levels of humidity should be analysed in detail in further studies. Likewise, the additions of white cement to the slaked air lime mortars (C:A) also increases the mechanical strengths, namely at early ages, even with similar open porosity values as the A mortar. However, probably due to its large volume of capillary porosity, these compositions present higher values of water absorption and the drying also occurs slower than for the lime-based mortars. In addition, the natural hydraulic lime mortar (NHL) shows greater mechanical strengths, even at early ages. However, despite the moderate values of water absorption, this composition shows a slower drying process. Additionally, the presence of soluble salts on the surface of the specimens after the capillary water absorption cycles could have mechanical repercussions and cause decay of the renders, as well as of the substrate. A decrease in mortar performance is observed with the addition of nanosilica (A+NS3% and A+NS5%). In general, with early curing times, a noticeable increase in the compressive strength values could be observed, even with a very high percentage of porosity. However, at longer curing ages, a steep decrease was recorded, namely in the mortar with 5% of nanosilica (A+NS5%), which was related to the microcraking of the matrix associated to shrinkage strains, which could interfere in strength development in the long term, which can thus limit the use of NS in lime mortars for conservation purposes. This problem could probably be controlled with a humid long curing, but such conditions are very difficult to guarantee in real works. Moreover, mortars with the addition of NS present the highest values of water absorption, and their drying occurs faster than for the other mortars due to their high pore connectivity. Furthermore, when subjected to a few water absorption/desabsorption cycles, the specimens evidence high fragility. Regarding the global results of the samples, the use of A+Q30% and C:A mortars seem to present the best global performance. Thus, in order to approach the original formulation with regard to its composition and grain size distribution, as well as improve the mortar performance, a fine-tuning of the aggregate, substituting part of the siliceous sand by limestone aggregate in 30% (M\({}_{1}\)), 10% (M\({}_{2}\)), and 5% (M\({}_{3}\)) by volume was made. The laboratory results showed that the substitution, in general, decreases the porosity and increases the mechanical performance, as well as decreases the rate of water absorption of the two types of mortars, namely on mortar with 30% of sand substitution (M\({}_{1}\)).