Towards a better understanding of hot-mixed mortars for the conservation of historic buildings: the role of water temperature and steam during lime slaking

Abstract According to various historic accounts and material evidence, the practice of producing lime mortars by mixing quicklime with sand (i.e. hot-mixing) before first slaking it water was much more common in past centuries than appreciated most contemporary academics, conservation professionals craftsmen. However, last 10 years, there has been resurgence interest hot-mixing. In such systems, steam developed during is supposed be crucial determining superior characteristics mortars, but in-depth investigations on role hot-mixing are very few. This study reports results some experimental work investigating effects temperature used for related mortars. these tests, calcic slaked at 20 75 °C, 90 °C. Microstructure mineralogical hydrates were characterized scanning electron microscopy (SEM) X-ray diffraction (XRD). Mortars produced limes tested fresh (water retention flowability) hardened (compressive flexural strength) properties. Carbonation assessed using SEM, XRD phenolphthalein tests. Results show that steam-slaked characterised portlandite crystals smaller crystallite size significantly different microstructure compared water-slaked lime. also made have higher flowability Under conditions comparatively low relative humidity (c 40–50%), carbonation slower mortar due lower content Overall, confirm anecdotal better workability suggest this production technology, which only rarely nowadays, can produce improved characteristics, provide a means match performance create compatible materials restoration work.