**4. Conclusions**

This study aimed to develop lightweight hydrated lime injection grouts to be used for consolidation of larger decorative plaster detachments with historical value. A reduction of the grout's self-weight was performed by using glass microspheres as one of its constituents. In the 1:3 (volume ratio) hydrated lime: mineral filler grout, five volume ratios of limestone filler (LS) to glass microspheres (GM) were studied: 100%:0%; 67%:33%; 50%:50%; 33%:67%, and 0%:100%. Adequate workability was evaluated by a conservator—via injection of the grout through a syringe—and was set as the requirement for the grouts in the fresh state. Based on the test results obtained, the following main conclusions were drawn:


**Author Contributions:** Conceptualisation, A.P. and V.B.-B.; methodology, A.P. and V.B.-B.; validation, V.B.-B.; formal analysis, A.P. and V.B.-B.; investigation, A.P.; resources, V.B.-B.; writing—original draft preparation, A.P.; writing—review and editing, V.B.-B.; visualisation, A.P.; supervision, V.B.-B.; project administration, A.P.; funding acquisition, A.P. and V.B.-B. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was undertaken in a framework of the project C3330-17-529030 "Raziskovalci-2.0-UL-FGG-529030". Ministry of Education, Science and Sport of the Republic of Slovenia has approved the project. The investment is cofinanced by the Republic of Slovenia and the European Union under the European Regional Development Fund. The authors also acknowledge the financial support from the Slovenian Research Agency through the research core funding No. P2-0185.

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