**4. Conclusions**

From the results of the experimental campaign, it was concluded that the incorporation of wool fibers in rendering mortars presented a satisfactory performance concerning the mechanical and cracking behavior. All of the modified mortars presented less susceptibility to cracking when compared with the mortars without fibers, based on the parameters evaluated.

In general, the reinforced mortars presented a decrease in the dynamic modulus of elasticity, which can be considered an advantage of the incorporation of wool fibers. W 3.0\_10%c and W 1.5\_10%cl obtained a similar decrease of 20% of modulus of elasticity when compared to the control mortar.

Regarding flexural strength, the modified cement mortars presented an increase when compared to the reference mortar. The addition of longer fibers enhanced the mechanical strength of the mortars. W 3.0\_20%c obtained an increase of 40% in flexural strength when compared to REF 1:4. The cement-lime modified mortars obtained a slight reduction in flexural strength, with the exception of W 3.0\_10%cl.

The dynamic modulus of elasticity and flexural strength ratio (E/σf) was analyzed as an indicator of the mortars' ability to resist cracking. It could be seen that all of the modified mortars, regardless of the binder used, presented a lower (E/σf) ratio, which could lead to a lesser tendency to crack due to restrained shrinkage when compared to the reference mortars.

The ratio (σf/σc) is related to the mortar's ductility. According to the results, all the modified mortars presented a higher ratio (σf/σc) compared to the reference mortars, which allows concluding that the incorporation of fibers increased the ductility of those mortars, based on this parameter.

Regarding fracture toughness, the modified cement mortars presented improvements. In fact, the toughness increment was higher when longer fibers were incorporated. However, for the cement-lime mortars, the toughness results did not present any significant contribution of the incorporation of the fibers.

Besides the analyzed parameters related with the cracking behavior, it was also found that, concerning compressive strength, the incorporation of longer fibers in cement mortars (W 3.0\_10%c and W 3.0\_20%c) resulted in an increase.

The results obtained in this work identify the advantages of the addition of the natural wool fibers in rendering mortars, namely concerning the improvement in the mechanical, and in particular of the cracking behavior.

**Author Contributions:** C.M.P. performed the experiments in the Building Finishes and Thermal Insulation Unit (NRI) of the National Laboratory for Civil Engineering of Portugal (LNEC). The analyses of the tests and the interpretation of the results were developed by C.M.P., R.V. and J.d.B. The original draft of this paper was written by C.M.P. and the review and editing were performed by R.V. and J.d.B.

**Funding:** This research was funded by Portuguese Foundation for Science and Technology (FCT) (PD/BD/135193/2017).

**Acknowledgments:** The authors would like to acknowledge the REuSE project from National Laboratory for Civil Engineering of Portugal (LNEC) and the research unit CERIS from Instituto Superior Técnico (IST).

**Conflicts of Interest:** The authors declare no conflicts of interest.

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