Today we're talking about hydraulic lime , a binder used since ancient times for the construction of a wide variety of architectural works. In modern times, it has faded into the background, especially with the advent of cement. In reality, its characteristics are valuable , and its use is still widespread today, especially among those seeking to combine durability with environmental friendliness. So, let's start with the material's origins and delve into the advantages of hydraulic lime , a perfect example of an ecological and environmentally friendly binder.
What are hydraulic kicks?
Hydraulic lime is a calcium hydroxide-based binder that sets and hardens upon contact with water. Specifically, it is a product derived from the calcination of marl, a particular type of limestone containing more than 6% clay. The material's main characteristic is its ability to set and harden when immersed in water: the chemical process underlying this phenomenon is colloidal hydrolysis , which gives the final mixture extremely high mechanical strength, especially when compared to that resulting from the processing of air limes.
If you're looking for a more precise definition of the term hydraulic lime , here it is. Hydraulic limes are products derived from the firing of marly limestone or calcareous marl at temperatures between 1000 and 1250°C.
The origins
We mentioned it at the beginning of this article: the use of hydraulic limes is very ancient. They are, in fact, a true milestone in the history of binders, at least until the "discovery" of Portland cement. The first to use them (albeit with different formulations) were the ancient Greeks and Romans . However, it was not until the late 1700s that the mechanism underlying the reaction of hydraulic lime was discovered , linked to the presence of clay impurities. It is no coincidence that the adjective "hydraulic" was added by engineer Luis Vicat, who understood the necessary ratio between the clay and limestone components for the compound to harden with the sole presence of water.
Luis Vicat's merits also include having provided for the classification of hydraulic limes , which he grouped into "weakly hydraulic", "moderately hydraulic" and "eminently hydraulic". Today this subdivision is obsolete, having been replaced, at a European level, by the EN 459-1 standard, which divides natural hydraulic limes into NHL 2, NHL 3.5 and NHL 5.
The advantages of natural hydraulic limes: why use them
Having discovered the definition and history of these binders, let's move on to the many advantages of natural hydraulic limes . We've listed them below for easy reference.
- They are strong and resistant: hydraulic kicks acquire strength over time, while remaining flexible and consequently making any expansion joints superfluous.
- They are eco-friendly: this binder is a greener material, especially compared to cement. Hydraulic limes, in fact, are cooked at lower temperatures and, moreover, are made of natural and recyclable raw materials.
- They are breathable, while remaining impervious to water: they avoid the formation of condensation and humidity and, for this reason, fight the generation of mould.
- They fight pollution, even indoors, because they have a very low emission of VOC, or volatile organic compounds
- They are beautiful to look at and feature highly prized natural colours. For this reason they are also used in contexts characterized by landscape restrictions and are used for restoration works in general.
Natural flooring and hydraulic limestone
The characteristics of hydraulic lime make it an excellent binder for natural pavements , which, in addition to being durable, must also be draining. The material's inherent flexibility makes the pavement particularly efficient, capable of lasting over time and withstanding the natural freezing and thawing cycles of the ground. The natural nature of the binder also makes it perfect—including in terms of landscape impact—even in highly historical contexts or along nature trails.
It should therefore come as no surprise that Terra Solida , a leader in the sector for the creation of natural flooring, makes such extensive use of hydraulic lime in its eco-friendly binder mixes.
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