Slaked lime: pros and cons

Slaked lime is the main component of various coatings, mixtures and solutions, which gives them high performance characteristics. The most unique material, known since ancient times, is available in preparation, is stored for a long time, has disinfectant properties, is widely used in industry, household, valuable for the garden and vegetable garden.

A wide range of lime applications is also due to its low cost.

What it is?

Lime is an industrial product used in metallurgy, construction industry, pulp and paper and chemical industries and for agricultural purposes. In considerable volumes and with significant benefits, it is used in solving environmental problems (treatment of waste water and harmful gases).

In European countries, its consumption reaches 80 kg per person per year.. The total production of the product in the world reaches 300 million tons per year. In Russia, up to 10 million tons of lime are produced every year, of which 4 million are for construction. It is obtained by firing until the maximum release of carbon dioxide from calcium and magnesium rocks. Carbonates are used as raw materials: limestone, chalk, shell rock and other materials.


Slaked lime (fluff) or calcium hydroxide (Ca (OH) 2) is a chemical compound of a powdery structure of a whitish color, slightly soluble in water, with characteristic astringent and plastic qualities. As a result of hydro-quenching, it actively interacts with acids in neutralization reactions.

Particles of calcium in the composition of the substance retain water well, therefore these mixtures do not freeze as quickly as cement. This is precisely the main advantage of lime mortars – the setting time makes it possible to qualitatively level the surface with a smooth and thin layer. In addition, the product adheres perfectly to brick and concrete textures, which provides the necessary strength after hardening..

If the hydroxide is not used for a long period of time, then the reverse process, which occurs with the absorption of CO2, leads the composition to a solid state. On sale, fluff or lump lime is most often found..

Advantages and disadvantages

The main advantage of the product, perhaps, can be attributed to the vast scope of its use and low manufacturing cost. In addition, during the production of many works with it, there is practically no waste, which brings undoubted economic benefits..

The product perfectly absorbs moisture, which allows it to be effectively used as a full-fledged component in the preparation of solutions and mixtures with enhanced strength characteristics. The hydration process occurs violently, with abundant heat release (exothermic reaction), which ensures uniform solidification of the composition and additional hardening of its surface.

More broadly, we will consider the advantages and disadvantages using the example of a widely used lime plaster with slaked lime in the composition:

  • undoubted thermal insulation qualities – plaster allows you to keep warm in the premises, and therefore save on heating;
  • fire safety – does not burn and does not support combustion;
  • convenient to work with, since it is plastic and does not quickly freeze, that is, it simplifies the workflow;
  • hygiene – an alkaline base counteracts the appearance of mold and mildew;
  • vapor permeability – prevents moisture accumulation;
  • mechanical strength – the surface of the plaster does not crack even when nails are driven into it.


  • Duration of solidification. When applied in layers on the wall (it is necessary to wait for the previous layer to dry), the repair time is significantly increased.
  • The time for self-slaking of lime is about two weeks or more..
  • Lime plaster is not recommended for use in places with high humidity. For example, in the bathroom it is better to use a cement-lime mortar..


The preparation of lime is regulated in detail by state standards. Structurally, the product consists of carbonate substances, mineralized additives (blast furnace or electrothermophosphoric slags, quartz sands and other inclusions). Each additive has its own regulations. Any component of the composition in a known way affects the physical qualities of the product, accordingly, its consumption per 1 sq. m.

Air quicklime is produced in three grades (1, 2, 3); quicklime powder – two varieties; hydrated, without additives and with them, is divided into first and second grade.

The dispersion of the first and third types must meet special conditions – during sifting of material samples through a sieve (mesh No. 02, No. 008, GOST 6613), at least 98 and 85% of the entire sample must pass, respectively.

The speed and complete completion of the quenching reaction, the amount of waste and the level of the final quality of the material depend on numerous factors, among which are the quality of the grade, the level of ability to react with chemical reactions, fractional parameters of raw materials, the speed and quality of mixing the components of the mixture, the volumes of water used, the temperature state of the reagents, methods quenching, processing elements and product holding time. The certificate of conformity of a product includes information about its grade, amount of impurities and condition.

From the point of view of ecology, lime is an environmentally friendly material that disinfects premises well, resists the development of fungi and negatively affects harmful bacteria. Whitewashing the premises facilitates the penetration of air into them (the surface “breathes”). Lime is not dangerous for allergy sufferers.


Firing results largely depend on the technology used, which allows you to distinguish a number of types of lime:

  • Quicklime lump – “boiled”.
  • Burnt ground (flour) – dry powdery consistency obtained during the grinding of the first.
  • Slaked lime (hydroxide), or fluff, is a finely dispersed powdery product produced during the slaking of lump lime (“boiling water”) with a fixed volume of water. The main composition is Ca (OH) 2. Against quicklime material, the percentage of moisture in the hydroxide should be from 60 to 70%. Usually fluff is sold packaged.
  • Lime dough (paste) – derived from the quenching of raw materials (“boiling water”) with large volumes of water. The consistency is similar to the dough. Water consumption is about 3.5 times more than for making fluff.
  • Lime milk is a thickish consistency of light shades, obtained by mixing with water in a ratio of 1: 10. It is used in the processing of premises, facades, outbuildings, in gardening.

The higher the quality level of the feedstock, the higher the percentage of CaO in the product, and hence the yield of Ca (OH) 2 in the quenching process. The low quality of raw materials is associated with an increase in the amount of CO2 in it, which occurs due to its underburning and the formation of calcium carbonate (CaCO3), the pieces of which are easy to detect by weight – they are heavier than completely burnt pieces. With the growth of calcium carbonate, the waste increases. The smallest volume of waste has a product of the first grade and moderate – of the second..

Of the limestone hydrates, so-called freshly slaked lime is often used, which is used no later than six hours after slaking. It is used for the preparation of lime milk.

As a viscous inorganic in combination with asbestos fibers, lime acquires specific qualities, forming a number of valuable derivatives (asbestos cardboard, asbestos paper). Based on its intended use, various components are added to the composition.

Lime is classified according to several criteria (signs).

By the time period spent on extinguishing:

  • quick-extinguishing – within 8-10 minutes;
  • medium damping – about 25 minutes;
  • slow extinguishing – more than 30 minutes.

The first and the second have become widespread in the metallurgical and construction sectors, in the chemical industry (fiber production), in agricultural activities (soil liming), in medicine..

By types of hardening:

  • air hardening, used to ensure the hardness of building mortars in an open environment;
  • hydraulic hardening – used to form high-strength mixtures, often for work in water (bridges, port foundations, etc.).

By the size of fractions:

  • lumpy – sold in bulk;
  • crushed;
  • powdery.

In addition, lime is subdivided into:

  • air, which is divided into 3 subgroups: dolomite, calcium, magnesian;
  • hydraulic, containing about 20% alite and belite, used both in air and under water;
  • chlorine (bleaching);
  • soda – compounds of soda and hydrate used to absorb harmful gases (respiratory and diving equipment).

Cement, gypsum and clay are used as binders for the formation of mixtures of various purposes..

For safety reasons, lime is transported closed.

Scope of application

The scope of application of hydroxides is truly enormous..

They have been used for the preparation of special mixtures and masonry since ancient times.. Traditional recipe: three to four parts of sand are mixed to one part of the mixture of fluff and water. In the process, water is released, which is a negative aspect, since high humidity is retained in rooms built using such a material for a long time. Therefore, cement as a binding element and displaced lime on construction sites..

Lime is also used for the manufacture of silicate materials, the hardening process of which is accelerated, since the mixture of calcium oxides and quartzites is affected not by water, but by steam heated to 190 ° C with a pressure of 15 atm. To do this, use special devices called autoclaves..

Lime is also used:

  1. in the process of water softening;
  2. in the production of bleach;
  3. when receiving fertilizers and neutralizing acidified soils;
  4. in the process of causticizing carbonates;
  5. in leather tanning;
  6. in order to obtain other chemical compounds, in the reactions of neutralizing acidic compounds (industrial, waste water);
  7. as food additive (E526);
  8. to identify CO2, interacting with which it becomes cloudy;
  9. as a means of disinfecting dental tissues in medicine;
  10. for grounding equipment in soils with an excessive level of resistance (reduces the degree of soil resistivity);
  11. milk of lime is used for the manufacture of fungicides;
  12. to scare away rodents by adding to the soil;
  13. in brickwork, especially oven, as it provides excellent adhesion to brick or cinder-concrete texture;
  14. for wood finishing using plaster mesh (shingles);
  15. for high-quality insulation of walls in the chicken coop.

A separate topic is the use of fluff for soil cultivation..

It is mainly used to correct the soil condition..

The dosage of the drug depends on 2 aspects:

  • the composition of the soil and the degree of its acidity;
  • type and depth of placement of funds on the site.

The level of an overestimated degree of soil acidity is identified by the following signs:

  • the presence of a whitish, ash layer on the soil;
  • unsatisfactory growth of clover on the soil;
  • heavily overgrown mosses, sorrel, wild rosemary, whitebird and other plants that love an acidic environment.

To more accurately identify the level of soil acidity, its samples are taken to a special chemical laboratory or pH meters and known indicative means are used.

Soils are distinguished according to the pH level:

  • strongly acidic – pH 4;
  • moderately acidic – pH 4-5;
  • slightly acidic – pH 5-6.5;
  • neutral – pH 6.5-7;
  • slightly alkaline – pH 7-8;
  • medium alkaline – pH 8-8.5;
  • strongly alkaline – pH 8.6 or more.

Neutral soils and below are not subject to processing.

It is important to take into account that for each specific agricultural crop and type of soil, the volumes and parameters of the applied fertilizer differ..

How to breed?

It is not difficult to prepare the target composition of the substance..

To do this, you need to know that a number of lime solutions are distinguished:

  • Gypsum-lime. Grabs within 5-10 minutes. Therefore, it is made in small volumes and immediately applied to the surface. The final hardening time is from one day to two. The coating is durable and easy to handle. Cornices and other wooden elements are finished with this solution..
  • Cement-lime. The mortar is highly durable and moisture resistant. Used in basements and bathrooms. Use cement M400 (for strength) or M200. The mixture is prepared at the rate of 1 share of cement and lime to 3 shares of sand.
  • Clay-lime. It is used less often, but it has excellent strength properties. It is important to consider that clay is an inexpensive and environmentally friendly material. Mainly used for working with clay objects.

To turn lime raw materials into plaster, it must be extinguished. The entire blanking procedure takes an average of 36 hours. However, the slaked lime must be aged for up to 15 days. In the process of extinguishing, it is recommended to adhere to safety rules, since the reaction is pronounced exothermic..

Wear protective goggles, gloves, boots and rough clothing.

Containers are usually used in metal. During the reaction, the mixture grows in volume by about 3 times, which is important to take into account when choosing a suitable container.


  • for fluff – 1 kg per 1 liter of water;
  • for dough – 1 kg 0.5 l.

During the process, the raw material is filled with cold water. At the end of the procedure, the resulting mixture is mixed and allowed to stand. Next, the product is passed through a sieve.

Then they start producing plaster mortar, for example, based on cement. Mixing proportions vary depending on the type of solution and the purpose of its use..

Cement-lime plastering mortar satisfies many types of work. For its manufacture, cement M400-500 is usually used, as well as sifted sand of medium fractions. It is easy to make a plastic consistency for finishing work: 25 kg of cement, 14 kg of lime, 230 kg of sand, 60 liters of water. For a more durable solution, the proportions are somewhat different: 25 kg of cement, 7 kg of lime, 175 kg of sand, 55 liters of water.

For elasticity, productive adhesion and increase moisture resistance, solutions are improved by adding liquid soap (0.2 l per 20 l of the mixture) or PVA glue (0.5 l per 20 l of the mixture).

Thus, the whole procedure looks like this: cement and lime are placed in a certain volume of water, mixed, sand is added.

After the formation of a homogeneous consistency, the remaining liquid is drained, and the solution is mixed again.

Subtleties of use

The product is also effective when carrying out repairs, for example, for whitewashing walls. In these cases, a hydrator is often used for slaking – a device for automated slaking of lime and obtaining hydrated lime (fluff). The required composition is prepared in advance, a day or two before the main operations. In order to obtain rich and light tones of diluted fluff, a ratio of 1: 1 is observed. A thoroughly mixed solution is applied to the material with a brush or using a spray gun in 2-3 layers.

Fluff is often added to various formulations.. So, added to cement, it forms a viscous consistency that does not crack even after drying..

Slaked lime with its characteristic fire resistance is used to cover wooden elements of houses in 1-3 layers. This eliminates rotting processes and improves the quality of the wood..

Lime is a caustic substance, therefore, when working with it, it is important to adhere to safety measures:

  • work in special glasses and gloves;
  • during the extinguishing process, you should keep away from the container where the reaction is taking place, since the latter is so active that you can get burned from flying splashes;
  • protect the respiratory system with a cotton-gauze mask;
  • in case of contact with the skin, it is necessary to remove the drops with a cotton swab soaked in vegetable oil, and place a compress of gauze previously treated with 5% vinegar on the injured place;
  • if the mixture gets into your eyes, rinse them immediately with water and, if necessary, go to a doctor.

Tips & Tricks

It is necessary to whitewash trees in autumn and spring, this procedure protects them from freezing and pests.

Experts recommend the following composition for use:

  • 10 liters of water;
  • 2.5 kg of fluff;
  • 0.1 kg of wood glue;
  • 0.5 kg of copper sulfate;
  • a handful of dried hellebore (scares away hares).

The components should be mixed until smooth. Then stand for 4-5 hours. The composition is applied to the trees with a brush or sponge. It is better to apply several layers..

Another useful recipe:

  • add 2 kg of slaked meat, 1.5 kg of clay and 0.3 kg of copper sulfate to a bucket of water (8-10 l);
  • when stirring, a viscous, like sour cream, composition is obtained;
  • the substance is applied to the wood without smudges;
  • the applied layer should be 3-4 mm.

Fluff is often used to decontaminate garden tools. Freshly quenched product is used. Lump raw materials are diluted with water (1: 1).

Milk is prepared from the resulting fluff (10-20% mixture):

  • 1 kg of raw materials take 1 liter of water;
  • dilute the cooled intermediate product with 9 liters of water;
  • use milk as directed.

Lime whitewashing is appropriate in rooms with high humidity.

However, it should not be used in vegetable storage areas with a moisture content of 10-20%..

If the composition is intended for masonry, it should be stored in a pit for at least a half month. If the dough is intended for the preparation of plaster mortar, then the period is about 1 month.

To replace lime, builders often use its analogues (“Azolit”, “Cemplas”, Zetesol), which are typical plasticizers with various specific qualities. For this reason, the choice of a particular plasticizer is made taking into account the specific conditions of use..

By adding lime to the sawdust, you can get an excellent insulation that is not subject to the decay process. Sawdust prepared for this purpose is mixed with fluff (10% of the sawdust mass). The resulting material is thoroughly mixed in a container, after which the voids are filled with it..

Solid materials are also prepared from sawdust and lime. This requires 10% lime, 5% gypsum and sawdust. The dry mixture is mixed and diluted with water until a thick consistency is obtained, which is immediately applied. The consistency is prepared in small volumes, since the gypsum hardens quickly.

Bleach is widely used for water purification, which avoids various epidemics.. In water, chlorine in combination with other substances can cause intoxication. In order to reduce the effects on the body, it is important to drink filtered water, previously using charcoal or other effective filters.

Before whitewashing, the treated area should be carefully cleaned of various residues: greasy stains, efflorescence, dirt and rusty spots..

Previously, the surface is plastered and primed, depressions and bulges are leveled. Unprocessed elements are covered up.

                      Whitewashing is done in 2-3 layers. The next layer lays down more reliably when the previous one is not completely dry, but slightly damp. In this case, the adhesion of the coating is improved. Before starting whitewashing, it is useful to moisten the surface.

                      There are several types of spray guns on sale: pneumatic, electric and manual. Manual is the best option for small areas. Electric ones are used for large areas, they spray the material more evenly.

                      If you add a pinch of ordinary blue to the milk of lime, then its color will turn into snow-white. Whitewashing will not stain clothes and hands if you add a little rock salt (100 g per 10 l) to the milk. Dilute salt correctly in a separate container..

                      For how to extinguish lime, see the next video.

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