Mortar is a homogeneous mixture resulting from the union of sand, water and an inorganic binder, which can be lime, gypsum or cement.
This variability of the binder is what gives rise to the classification of mortars according to their composition, which will be discussed in depth later.
Composition of mortar
In a basic scheme, the composition is defined by three elements, although it is worth mentioning the possibility of adding additives, which give particular characteristics to the mortar, thus giving rise to more types of mortar.
The essentials of each component are explained below:
Conglomerant
This is the key component, since it is responsible for creating the complete bond between the sand and the water, producing a homogeneous and stable substance.
Commonly, its structure is composed of very fine particles such as a powder, or it may have a pasty consistency structure.
The most commonly used binder is cement, followed by lime and gypsum. Any of these elements when reacting with water (hydration) produces the mortar mix, in a plastic state.
This will subsequently become rigid, due to the fact that the paste has been lodged in the interstitial spaces of the sand.
Statistically, the amount of binder is directly proportional to the shrinkage of the mortar.
Sand
Unlike the previous one, this component, sand, is the one with the highest proportion in the mixture; from 40% to 80%.
It is a mineral and granular material, which can be limestone or siliceous in nature and whose maximum size must not exceed 4 mm.
This component is the cornerstone of mortars, the basis on which the hydration of the agglutinant is carried out, as it is an inert material, unable to react chemically with other compounds.
La arena controla la retracción y contribuye a la resistencia mecánica.
Water
This element is responsible for providing the chemical environment conducive to the hydration of the binder, and is therefore the main cause of the plasticity of the mortar.
The amount of water in the mix varies according to the thermal conditions, the binder, the amount of sand and the expected consistency.
In addition, this amount is inversely proportional to the mechanical resistance of the mortar, but is directly proportional to its retraction and porosity.
The mixing water should have a minimum pH of 5, as well as low concentrations of sulfate and chloride ions, carbohydrates and organic compounds.
Additives
Admixtures can be of organic or inorganic nature, and they introduce modifications in the magnitudes of the characteristics of the plastic state of the mortar. They can be liquid compounds (emulsions) or powders.
Most of them are rheological or setting modifiers. And their proportion in the mortar mix depends on the amount of cement; on its weight.
In addition, there are compounds called additions, which configure the characteristics of the hardened state of the mixture.
There are even pigments and fibers that alter other aspects of the traditional mortar.
Types of mortars
The best known classification of mortars is determined by the type of binder.
The main types of mortar are the following:
Cement Mortars
They are mortars with the typical composition of sand and water, and the cement acts as a binder. They are characterized by high compressive strengths.
Their workability depends, consequently, on the amount of cement and sand, so sands with traces of silt and clays are usually used to improve this aspect of the mixture, although this affects its resistance.
Lime mortars
This is the traditional mortar, composed of sand, water and lime, which can be aerial or hydraulic. Aerial lime is the most commonly used, using white lime or gray lime (dolomitic).
The sand in these mixtures plays a very important role, since it must regulate the cracks due to contractions of the mass during the carbonation reaction.
Bastard mortars
They are so called because they arise from the combination of 2 binders. The most commonly used combination is the one that links lime with cement.
It is probably the most efficient type of mortar, due to the fact that it acquires a suitable consistency for workability. In addition, it has a good water retention and a high resistance value.
However, the magnitudes of each characteristic depend on the numerical dependencies of the components.
Uses of mortar
From a general point of view, mortars can perform a structural function, so they can be used in the construction of structural elements, or they can perform masonry functions, serving as glue or filler.
Additionally, mortars can function as coatings, being used as plasters, plasters or plasters.
Taking into consideration the aforementioned, we have a further classification of mortars, this time according to use:
- Sticking mortars: due to the special conditions of the construction system of which it is part, it has to possess special properties, such as considerable resistance to absorb stresses.
- Filling mortars: suitable for masonry, these mortars are usually used to fill the space of cells in walls, for example.
One requirement is that they must develop a good resistance, comparatively similar to the previous mortars.
Covering or plastering mortars: their functions are purely aesthetic, being in charge of generating uniformity and regularity on the surface of the element in question.
Resistance acquires a plane of almost null influence; the most important thing is consistency.