How To Make Concrete At Home

Here are some tips on the best products on the market and the best “recipes” for proportions, in order to prepare good quality homemade cement.

To obtain good quality, resistant and long-lasting masonry works, it is not enough to mix concrete as it happens. To begin with, it is necessary to know how to mix cement and sand in the right proportions , in order to obtain a homogeneous mixture that does not give rise to cracks during drying; in other words, it is extremely important to understand how to make cement , especially considering that the “recipes” change according to the type of mortar to be prepared.

So let’s go into the topic further, starting with how cement is produced and with which substances.

How concrete is made

Cement powder is obtained from raw materials containing calcium carbonate, i.e. limestone or gypsum, and aluminum silicates, mostly coming from clays. These substances are pulverized and then cooked in ovens at 1,300-1,500 degrees Celsius, where they bind without melting and give rise to clinker , the latter is subsequently ground and added to a small percentage of gypsum in order to obtain Portland cement, which it is the basic component of most types of cement used in construction.

There are five different classes of Portland cement identified by Roman numerals and, with the exception of class I, all the others give rise to further subtypes of cement.

Here is a good selection of cements , for those who want to buy them online.

The other ingredients

Mortar and concrete are mixtures where, apart from cement and water, there are also other components used as aggregates; usually crushed stone, gravel or sand depending on the type of mixture to be obtained.

To make concrete, for example, it is necessary to add coarse-grained aggregates to the cement paste, therefore mostly gravel and gravel; for the mortar, on the other hand, sand is used which is a finer aggregate. Furthermore, by adding a certain amount of lime to the cement-sand mixture , it is possible to create the so-called bastard mortar, which is used above all for the creation of walls and plasters.

Cement and water without sand , on the other hand, are the components of the grout , or the cement paste to which the granular aggregates are then added; grout alone is never used to carry out masonry works, but only for small finishing works such as filling the joints between tiles, for example, or as a waterproofing agent for roofs.

Sand and cement: doses

The most important step, therefore, is the one related to the dosage of the ingredients used in the mixture.

The ratio of cement, sand and water to obtain a good quality mortar must be respectively 1: 4: 1, i.e. one part of cement, four parts of sand and one part of water, while that for concrete is 1: 2 : 4: 1, that is, one part of concrete, two of sand, four of gravel or gravel and one of water.

The proportions must be calculated in volumes of course, but for those who wonder how many shovelfuls of sand are needed for a sack of cement , the answer is about 20; moreover, it is preferable to mix the cement and aggregates dry first, in order to make the mixture more homogeneous when adding water.

For the bastard mortar , however, the doses are different, in fact one part of cement, one and a half parts of lime, six parts of sand and a variable quantity of water are required depending on the desired consistency.

How to mix the ingredients

Before we mentioned the importance of dry mixing the various components of the dough, regardless of its type, and only then add the water. If you use the shovel instead of the concrete mixer , you will have to work the mixture with greater patience and attention, turning it over several times, in order to make it as homogeneous as possible.

Furthermore, the water should not be added all at once but divided into two or three parts; in this way it is possible to keep the consistency of the dough under control and prevent it from becoming too fluid.

It is important that the water is neither too cold nor too hot, but at a temperature of about 20 ° Celsius, in order not to alter the setting times; moreover it must be as clear as possible and free of organic acids, humus, silts, sugary substances, alkalis, clays or other substances that could alter or irreparably compromise the strength characteristics of the cement.

The resistance classes

Each type of concrete, in fact, has its own specific class of resistance to compression and traction, which is indicated by a number and a letter: 32.5N, 32.5R, 42.5N, 42.5R, 52.5N and 52.5R.

Cements with resistance class 32.5 are suitable for normal masonry works, while those belonging to classes 42.5 and 52.5 are used for works that require greater resistance, such as pillars, floors and pillars for example. The differences between cements with the letter R and those with the letter N also lie in the degree of initial and final strength; the maximum degree of resistance of a cement, in fact, is reached only when it is completely dry.

The taking times

One of the reasons why particular care must be taken when adding water to the mix is ​​that a disproportionate amount can significantly lengthen hardening times and compromise the strength of the cement.

Initial setting times vary from 75 minutes for class 32.5 cement up to 45 minutes for class 52.5 cement; 32.5R, for example, can be considered relatively dry at a distance of about three days from preparation and casting, but at this point it reaches a compressive strength of about 10 out of 32.5 and it is necessary to wait for complete drying to reach the maximum value.

Regardless of the strength class and the type of cement, in fact, the standard period of time required for complete drying is 28 days. When mixing concrete at home for small renovations, therefore, take this factor into account and equip yourself to keep yourself busy while you wait; maybe it’s the right occasion to buy one of the best acoustic guitars and learn how to play it.

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