Lime mortar

The lime mortars are those mortars that are made with lime, sand and water.

The lime used can be air or hydraulic, with the difference that it carbonates in contact with air (air) or sets in water (hydraulic).

In Spain, the type of lime is regulated by UNE UNE-EN 459-1:2011 (Lime for construction. Part 1: Definitions, specifications and conformity criteria), UNE-EN 459-2:2011 (Part 2: Test methods) and UNE-EN 459-3:2012 (Part 3: Conformity assessment).

Aerial lime

Aerial lime in traditional construction

Lime was already known in the 6th millennium BC. C. as a construction material for mortars and coatings. In Çatal Hüyük, walls plastered with lime mortar and painted in fresco have been found. Later, thanks to archaeological investigations, it has been verified that it was used in Ancient Egypt, the Assyrian Empire, classical Greece or the Roman Empire; Also, outside the Mediterranean, it was used by the Mayas, the Incas and the Aztecs in America and from the first Chinese dynasties or the first Indian dynasties.

It is very important to distinguish air lime from hydraulic lime, since the latter contains many silicates and behaves differently, especially as a construction material.

The air lime has very suitable properties since its mortars have the particularity of being permeable to water vapor (although not to rain) that allows the walls to breathe, which gives the walls hygroscopic qualities to regulate the humidity of the environments.

Once the lime is used, it begins to crystallize and carbonate, from the surface inwards, preserving a moist nucleus that is what gives it its properties and elasticity, thanks to which it has better mechanical behavior than Cement Portland, both for exterior and interior plastering, as well as for mortar and other uses.

After hundreds of years, slaked lime, after being completely carbonated, returns to its original composition in limestone quarries (calcium carbonate, CaCO₃).

Freshly slaked lime does not adhere chemically to surfaces, but mechanically. This makes it necessary to chip smooth surfaces for a correct adherence of the layers of rendering and rendering.

Other uses for air lime

Another use of lime is in "grout" to whitewash (paint) the walls and in some cases the ceilings with a broad brush. This painting has, like the renders, plasters, etc. of slaked air lime, a bioclimatic behavior in hot countries, due to its white color, which prevents solar radiation from heating the mass of the wall. To maintain these properties, it must be whitewashed again each year, usually in spring.

It is used in construction with rammed earth to stabilize the layers.

It can also be used for the creation of dirt roads by stabilizing the dirt while draining.

It can also be used to disinfect surfaces such as walls or prevent pests in trees by painting the surface of its trunk with whitewash. The paintings of numerous churches disappeared over the centuries under layers of lime that were put on when there were epidemics.

Lime slaking

Quick lime is calcium oxide (CaO). When it comes into contact with water, it reacts reaching a temperature of 90 °C, so care must be taken in the container where it is made: it should only be done in containers metal or certain plastics. During this process and afterwards, the lime becomes caustic and can cause very severe chemical burns.

The lime that comes out of the kiln where it was made is always alive, it has a large amount of calcium oxide and must be extinguished or killed >. Both air and hydraulic lime come out alive and therefore both types of lime, aerial and hydraulic, must be extinguished, although the way of extinguishing is different.

The usual use of lime is therefore already slaked in the form of calcium hydroxide, format in which it is usually purchased for construction.

When any amount of lime is put out, it could be stored in a "raft" or "rotten" for years, letting it continue to fade out and mature. The minimum period to be used is six months; the more years it spends resting, the better behavior it will have afterwards, carbonating optimally when used in renders, stuccos or mortars. Of course, not all lime quarries offer the same product quality and the higher percentage of carbonate a lime has, the better quality the slaked lime will have, which is calcium hydroxide (Ca(OH)₂), the ideal being those that are close to the composition of marble (calcium carbonate, CaCO₃).

During that maturation, however long it lasts, it remains caustic and any organic elements that fall into the "raft" it will end up disappearing devoured by the lime.

In ancient times, when the construction of a monument (cathedrals, palaces, etc.) began, the lime rafts were prepared, since it was the last element that was used in large quantities and since construction was very slow, in some cases it lasted more than a century, the lime was maturing by the time it was needed. The old lime makers said that the ideal lime was the one that had been resting for at least thirty years and they called it "girl" while the lime between twenty and thirty years old was called "boy".

Until just over a century, or a century and a half ago, depending on the area of Spain, when someone had a child, a lime raft was prepared for when he had to start building his house.^{[ citation required]}

Hydraulic lime

Hydraulic lime was created in France in 1821, since in this country the lime quarries, as in those of Belgium and Germany, produced a rock of poor quality with many silicates compared to the quarries in countries like Spain and Italy. Basically, hydraulic lime behaves in construction like white portland cement, but with worse results.

The French achieved its massive use by prohibiting the use of aerial lime in their colonies, especially in North Africa, and forcing the use of hydraulic lime.

Within the hydraulic limes there are natural hydraulic limes, which are natural, since they do not have any type of additive like cement and have much more resistance than air lime. If it is necessary to confer a certain hydraulicity to air lime, pozzolanic additives (traditionally ceramic fragments or volcanic aggregate) can be used. On the other hand, it can be used in the rehabilitation of old buildings as well as in bioconstruction, since it does not contain any type of sulfate, aluminates, salts, etc... that can damage the building to be rehabilitated or built.

The resistance of this type of lime is given by the addition of pozzolanic elements during the setting process, while in non-natural hydraulic limes its resistance is achieved by the combination of silica during the lime firing process.

Natural white hydraulic lime is especially recommended for restoration, rehabilitation and rustic finishing work:

• Interior, exterior and stone glazed.
• Set of bricks and old stones.
• General masonry.
• Paving in terracotta or stone.
• Placement of roofs (covers, smoothies, limehoyas, aleros).
• Reinforcement of argamasa.

Current studies on lime mortars

Currently, several faculties of architecture, physics and chemistry from the universities of Granada and Seville have coordinated to carry out documented field studies and theses on air lime using samples of aged lime >. This is a determining factor in its possible use by professionals since its use is currently completely unknown in the field of architecture and construction since it has not been taught in the faculties for almost a century in favor of more modern materials.. However, there are numerous groups, professionals and even public administrations that are carrying out numerous initiatives for the recovery of traditional materials and techniques. An example of a public initiative can be found in the National Plan for Traditional Architecture developed by the IPCE

The decrease in the use of this material has been caused, among many other reasons, by the appearance of new materials and by the current rhythms set by construction systems.