At first glance, it seems that there is nothing tricky in the preparation of mortar. I mixed all the necessary components, added water, kneaded and that’s it. But here, then all sorts of nuances begin. Knowing and adhering to a number of rules, you can avoid many mistakes and achieve the desired result.
A building (masonry) mortar is a certain mixture consisting of at least three components, which is used in construction to connect structural materials, in finishing and waterproofing works, etc.
As a binder, cement is usually used, sometimes gypsum, lime or clay. This component allows you to reduce friction between the particles of the aggregate used (sand, expanded clay, pumice crumbs) and give the mortar the mobility necessary for work. The most commonly used solvent is water.
Depending on the amount of aggregates and binders used, the mixture can be either simple or complex. An important aspect is that the prepared mortar before hardening must have a number of properties, such as easy to stack (the ability to lay the mortar in a thin and dense layer), plasticity (the ability of the mortar to spread under the action of external forces and the weight of the masonry material), strength.
Depending on the purpose of the mortar, it is divided into three main groups:
Construction masonry mixes. They are used for masonry work (stone or brickwork), foundation cementing, installation of large blocks or large wall elements. When designing a house, a special calculation is made, as a result of which the brand of mortar required during construction is determined (indicated by the letter M), which usually ranges from M50 to M150. To further increase the strength of the building mixture when performing basement work and during the construction of foundations, brick or gravel is specially added to the mortar. Masonry mortars, depending on the binder component used, are divided into cement, cement-clay, cement-lime and lime.
Basically, various types of Portland cement are used for the manufacture of these solutions. The lower the slag content in the cement, the better the masonry will be. When laying with face brick, be sure to use slag-free Portland cement to prevent the formation of flows and efflorescence on the walls.
Building finishing mixes. This type of solution is used for plastering ceilings and walls outside and inside the premises, applying a decorative layer, finishing slopes, making all kinds of decorative and design elements. Finishing mortars are characterized by a relatively long setting time and high mobility. In addition, the composition of this solution should not contain aggregate with a large fraction. Finishing mixtures are usually made on the basis of cement, cement-gypsum, cement-lime, gypsum and lime binders.
Gypsum and cement-gypsum mixtures are used exclusively for indoor decoration.
To give additional gloss to the finishing layer, a small amount of crushed glass or mica can be added to the solution.
Special building mixes. This type of building mixes includes solutions of narrowly targeted use, such as waterproofing, heat-insulating, “injection” for repairing floors, and others. Wood chips, metal shavings, liquid glass, bituminous emulsions, polymers, sodium aluminate, expanded clay chips and much more are added to such solutions.
Despite the wide variety of mortars, there are a number of general rules that must be followed in its manufacture. In the case of using sand as a filler, only sand of river origin is recommended, since other types of sand (for example, ravine) contain dust, clay and humus components, which significantly reduce the quality of the mortar.
In addition, expanded clay and shell sand can be used. Consider several ways to prepare mortar at home. The manual method of preparing the solution is one of the most popular, as it does not require additional costs for the purchase of mechanization. The manual method of preparing mortar is justified only with small volumes of construction. You can prepare the mixture both in a steel box, trough, old bathtub, and on a wooden shield or metal sheet. Cement and sand are poured in the form of small (not more than 200-300 mm high) beds, thoroughly mixed with a shovel or trowel until a homogeneous mass is formed, then they are closed with water and kneaded.
The ratio of sand and cement depends on the grade of cement used in the mortar (300, 400) and on what grade of mortar is to be obtained as a result. The most common compositions of mortar mixtures are presented in the table: Grade of cement Grade 50 75 100 Cement mortars (cement: sand) 200 1:4 1:2.5 – 300 1:4.5 1:3 – 400 1:6 1:4 1: 3 500 – 1:5 1:4
Cement-clay and cement-lime mortars (cement: lime or clay: sand) 200 1:0.3:4 1:0.1:2.5 – 300 1:0.4:5 1:0.2:3 – 400 1:0.7:6 1:0.3 :4 1:0.2:3 500 1:0.7:8 1:0.5:5 1:0.3:4.
The quality of the mortar, and, consequently, the quality and reliability of the brickwork, will depend on how thoroughly you mix the dry mix and the closed mortar. A solution that contains a dry fraction, lumps or an inhomogeneous structure will not perform its functions efficiently, it will quickly crumble and collapse. When mixing the solution, pay special attention to the corners of the container, where unmixed sand or cement usually remains. In the manufacture of the mortar, it is necessary to use a sufficient volume of water, since its excessive content will reduce the grade of the mortar, lead to separation of the finished mixture, washing out and shrinkage during hardening. Add water in small portions, constantly mixing the solution until a homogeneous “creamy” mass is formed.
Do not prepare the mortar in large batches as it will begin to set after 1-2 hours. It will be difficult to work with such a solution, and the quality of work will decrease significantly. The manual method of preparing mortar is a very time-consuming process. In order to facilitate the process of preparing the mortar, use special mortar mixers (concrete mixers). You will not only be able to reduce the complexity of this process, but also increase the quality of the prepared solution several times over. Preparing the mortar with a concrete mixer is very simple. Pour the required volume of water into the concrete mixer.
If gravel is used in this solution, then we fill it up. Then we add the required amount of cement, and lastly – dry sand. The blades in the concrete mixer will quickly and efficiently mix all the ingredients until a homogeneous mass is formed. Everything, the solution is ready. How to prepare the mortar – you choose. If you need a small amount, say, for plastering, then it is best to prepare it in a bucket, kneading by hand or using a special whisk attachment for a drill.
If you are building a cottage, then, undoubtedly, you will need a stirrer, which you can not buy, but rent for a few days. And if you need a very large volume of mortar at a time, say, for pouring a foundation, then the best option would be to order the delivery of the finished mixture by a cement truck (automixer). I pay special attention to the fact that it is better to prepare adhesive mixtures or lime mortar by hand, since when prepared in mixers, the components of the solution will constantly stick to the walls.
Recently, special additives that are part of building mixtures have become widespread.
They can be divided into several groups, according to their action:
plasticizers, special elements that reduce the need for a mixture of water, thereby increasing the strength and ease of placement of the finished mortar;
setting retarders or accelerators;
special additives that reduce the freezing point of the solution, which will become simply indispensable when performing construction work in the winter;
sealants, increase the degree of frost resistance and water resistance of mortars;
water-repellent additives that give hydrophobic properties to the hardened solution, in other words, the solution becomes completely resistant to water;
dyes, special substances that give the solution a certain color (mainly used when laying facing bricks);
modifiers that change the level of stickiness of finishing mixtures, reduce the elasticity of the mixture and its fluidity. Some additives have several properties at once.
It is necessary to mix additives with water strictly in the proportion indicated by the manufacturer on the package, and then directly prepare the mortar. We hope these recommendations and tips on proper mortar preparation will help you avoid common mistakes. Your built house will be strong, reliable, durable and beautiful.
We wish you all successful construction.