What Is And How To Prepare Cement Mortar

Everything you need to know about one of the most used conglomerates in construction, starting from the composition up to the different types and possible applications.

Mortar is mainly used in building and construction, technically speaking it is a conglomerate obtained by mixing a binder, mostly cement or lime, with fine aggregates (sand), water and any other additives. This shows the difference between mortar and cement , as the latter is a binder while the other is a composite material .
The proportions of the mixture are calculated in order to obtain a mixture that is easily workable when wet, but which once dry sets and hardens, acquiring high mechanical resistance.

The mortar was already known and used in the time of the Phoenicians, but was further perfected in Roman times, where it was used for the construction and waterproofing of aqueducts and cisterns, for dry stone walls and for the construction of large buildings.

Composition and preparation

As regards specifically the components of the mixture, the binders that are usually used are cement and lime, the latter, however, varies according to the type of mortar.

For aerial mortars, aerial and hydrated lime are used, the latter also used as an additive in cement mortars. The binders used for hydraulics, on the other hand, are hydraulic lime in powder, which can be of natural or artificial origin, eminently hydraulic lime, always natural or artificial in powder, pozzolanic lime, artificial pozzolanic hydraulic lime and hydraulic lime artificial steel industry.
Sand is used as a fine inert component; however this must come from sedimentary deposits or from the crushing of rocks, it must be free of organic components, sulphates, chlorides and other harmful substances, and the granulometric limit must not exceed 4 mm in 95% of the amount of sand used for the mixture.

Furthermore, the size of the binders and aggregates used for the mixture also makes the difference between the mortar and the concrete; both are conglomerates, in fact, but the concrete is made with aggregates that are larger than the mortar. The binders, on the other hand, are very fine powders that tend to disperse very easily in the environment during mixing, the only effective way to remove them is to use a professional vacuum cleaner .

The last, but not least, ingredient is water; in fact, this must be as pure, clear and sweet as possible, it must not contain organic or vegetable particles, silts, clays, alkalis, sugary substances and more, moreover it must not be too cold or too hot, in order to guarantee the right grip .

The quantity is also important, because it affects the characteristics of the mortar; a mixture with too much water in fact, even if it dries completely, is less resistant to traction and compression than a mixture obtained with a smaller quantity of water. As for the preparation, however, this is usually carried out by pouring the components of the mixture and the water into a concrete mixer of adequate size to produce the quantity of mortar necessary for use.

The classification of the mortar according to hardening

Mortar is characterized by two distinct processes: setting and hardening, which particularly affect the type of binder used in the mixture. The first classification of mortars, therefore, is based on the type of hardening: all those that set and harden only in contact with air are called aerial, while the hydraulic ones are able to set and harden even not in contact with the ‘water.

Consequently, aerial mortars have a more general use, while hydraulic ones are mainly used in civil engineering works such as bridges, tunnels, dams and port works for example, since they can also harden in contact with water or underground.

The classification of the mortar according to use

Another broader classification, however, is based on the intended use, which divides them by denomination. We therefore have the bedding mortar , commonly used as a binder for bricks, the finishing mortar, which is used to finish rough mortar systems, the stylus mortar which is used to close cracks or finish walls and floors of heterogeneous composition, the one to be injection, used for the re-joining of systems that have undergone detachments. The screed mortars are instead used in the preparation of the substrates on which the flooring will subsequently be laid, while the arriccio is a type of preparatory mortar that is applied before laying the plaster.

Other types of mortar

Aside from the two primary grading methods, mortars are subject to a wide range of different names used for commercial purposes. For the convenience of the buyer, therefore, especially if the latter is a private individual who is about to start a do-it-yourself renovation, it becomes much easier and more immediate to identify the product that best suits your needs.

Various types of mixtures can therefore be found on the market, both as regards the plasters and the mortar; one of the most sold, for example, is the premixed mortar , commonly known as ready-made mortar since it requires only the addition of water to be used. Among the various premixed varieties on the market, there are aerial and hydraulic types as well as cement mortar .

More commercial definitions that are pressed for this conglomerate, also addressed the scope hobby and crafts, are mortar building and mortar for masonry , in order to emphasize their intended use.

The bastard mortar and the plasters

We cannot worthily conclude the article on mortar without talking about two particular types of this conglomerate: the so-called bastard mortar and plasters. The first is so called because it uses both types of binders in its mixture, ie lime and cement; the bastard mortar is used above all for masonry works and as a bedding mortar, as well as a base plaster for interiors and exteriors.

The plaster itself, on the other hand, is a conglomerate that has the same characteristics as the mortar, in fact it is obtained with the same “ingredients” and the only difference consists in the granulometric size of the sand, which is never greater than 2 millimeters; for this reason it is also known as “fine mortar”.

Given the common characteristics, therefore, the difference between lime plaster and cement plaster is the same as that existing between similar mortar mixtures; the plasters, however, are mainly called upon to perform a protective coating function for the walls, and in some cases also an aesthetic function.

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