– one of the main stages of pre-finishing work, which affects the quality of repairs, durability and aesthetics finishing. Here, more often than others, lime mortar is used for plaster - durable, easy to work with, relatively inexpensive, and proven over time.
In the article we will tell you how to make a lime mortar for plaster, we will look at several recipes for preparing the mixture, how much lime to pour into the mortar for plaster, we will tell you about the advantages and disadvantages, we will make comparative characteristics regarding finished materials.
Where is lime-based plaster used?
Lime mortar for plaster can be called almost universal for external and interior works. Depending on the composition, the mixture is used for finishing residential and production premises, open balconies and loggias, outbuildings.
Lime plaster is afraid of a damp environment, so building regulations there are restrictions:
- It is not recommended to use the composition for finishing damp rooms: basements, bathrooms, on the facades of buildings in humid climate zones;
- According to SNiP, it is prohibited to use lime mortar for interior and exterior work where air humidity exceeds 65%.
The mixture should be thick and homogeneous
Composition of lime mortar for plaster - components, scope of application, recipes
The plaster mixture consists of a binder and fillers; simple or wallpapering compositions are created on a lime basis. decorative plaster walls and facades. The main difference lies in the components with which the lime dough will be mixed.
Preparation of lime mortar for plaster
For plastering, only hydrated lime is used, so before work the lump lime must be quenched; the process takes 36 hours until the reaction is complete, but it is recommended to let the solution sit for 2 weeks.
Important: The extinguishing process is accompanied by a violent chemical reaction, releasing a huge amount of heat. It is necessary to observe safety precautions: safety glasses, rubber gloves, boots, thick clothes.Containers for extinguishing: metal, without signs of corrosion, wood, plastic. Hydrated lime increases in volume up to 3 times, which should be taken into account when choosing the container volume. The process uses only cold water. Lime/water ratio:
- fluff (lime milk) in a ratio of 1 kg per 1 liter;
- dough - for 1 kg of lime 0.5 liters of water.
The lump lime is placed in a container, filled with water, the boiling process begins, after which the mass is mixed well several times and left to stand. Before use, hydrated lime is passed through a construction sieve.
Plaster
Lime composition with gypsum is suitable for finishing cornices and stone; it is not used for concrete surfaces. Scope of application: interior decoration of walls and ceilings; external use in exceptional cases. It sets quickly, half an hour is enough for complete drying, it is prepared in small portions, and cannot be stored in its finished form.
How to prepare gypsum-lime plaster for interior work: 1 part of gypsum for 4 parts of lime paste. Gypsum is mixed until it becomes sour cream, lime is added to the resulting mixture, the solution should be thick and not run off the spatula.
The lime-gypsum mixture is fine-grained and goes on smoothly.
Cement based
Cement-lime plaster is a complex, universal, durable mortar, suitable for all types of plastering work, including facades, finishing bathrooms, and basements.
The composition of cement-lime mortar for plaster depends on the application. For the mixture, cement of the M400-500 grade and sandstone of the middle fraction, sifted and washed, are usually used. The more sand, the weaker the solution.
Table of proportions of lime-cement mortar for plaster, solutions of different densities, calculation for 1 bag of cement (25 kg):
Cement-lime plaster is most often used in repairs. Specifications the composition can be improved with additives: for plasticity, maximum adhesion and increased moisture resistance, add liquid soap: 0.2 l/20 l of mixture or PVA glue: 0.5 l/20 l of solution.
How to prepare a lime mortar for plaster with the addition of cement: Add cement and lime to 2/3 of the total volume of water, mix, add all the sand, when the components are combined until smooth, pour out the rest of the water and mix well again.
Clay mixture
Clay-lime mixture for plaster is rarely used for finishing huts, stoves, fireplaces.
A popular recipe for how to make a clay-lime mortar with your own hands: the clay is soaked, ground through a sieve, mixed with lime dough, sand is added, proportions: 1 hour: 0.4 hours: 5 hours, then add water in portions, mix well until the consistency is very thick sour cream.
Lime-sand plaster with the addition of clay is not durable and is only suitable for rooms with a dry microclimate.
Eco-friendly mixture of lime and clay suitable for finishing stoves and restoring masons
Features and comparisons
Lime plaster mortar is used mainly indoors; it is much cheaper than ready-made store-bought mixtures, is not inferior to them in strength, and is easy to work with. The only negative that arises during the work process is how much lime to add to the plaster solution. To do this, we have given you several recipes for different types finishing.
Properly prepared mixture for plaster is the key to quality and durability of repairs
The finished mixture retains its properties for 6 hours, which should be taken into account when preparing the required volume. The consumption of lime mortar per 1 m2 of plaster is approximately 10-12 kg, with a layer thickness of 10 mm. The solution can be applied with a thickness of 0.5-30 mm, more thick layer will lead to peeling and cracking.
Now, it seems that preparing a solution for plaster will not pose any problems. Just like an ordinary person does: sifts sand, adds cement, mixes, adds water, mixes again and voila! Ready. But no. True professionals in their field will say that each plastering operation has its own solution. So let's take a look various ways preparation of mortars for plastering work, which consist of the following stages: preparation of sand, preparation and use of binding materials, and then preparation of the mortar.
Binders
Let's look at the main types of binders. The most commonly used materials are building lime, gypsum, cement or clay mixture.
Construction lime
The important thing is that building lime can only harden with access to oxygen. And depending on the degree of preparation, it can be divided into quicklime (aka “boiler”) and slaked (“fluff”). Remember! To prepare the solution, you can only use slaked lime, since all solutions are mixed with water, and when quicklime interacts with water, a spontaneous slaking process will begin. Then small unextinguished particles may remain in the solution, which interact with air moisture. As a result, the plaster will begin to swell. To extinguish the boiling water, it is better to use a barrel or box. Quickly quenching lime (8 minutes) is poured into a tank of water, which will cover the entire boiling pot. When steam appears, add water and mix thoroughly. Medium-slaking lime (25 minutes) is poured into the container a quarter full and filled with water up to half. When steam appears, stir the boiling pot and add water. If the lime is slowly slaking (from 25 minutes), then pour it into the tank and moisten it a little with water. Under the influence of water, the material will begin to deteriorate, and its volume will increase by 2-3 times. Then the temperature of the lime rises and it begins to “boil.”
As soon as cracks appear, start adding water in small portions and stirring slowly. In this case, all heavy particles will settle to the bottom of the tank. Then all types of lime are usually diluted with water until a full consistency is obtained, similar to milk of lime, which must be strained through a special sieve and poured into the lime slaking pit (pictured above). A day later, pre-sifted sand is poured on top, and then more earth in a total layer of up to 0.5 m.
Important! The boiling pot stays in the pit for at least half a month. Take your time and let the lime dry completely. Then the milk “turns” into dough, which has a creamy consistency.
The next binding element is building gypsum, which is used in plastering work as an additive to the lime plaster solution and allows to increase the quality of the mixture. When diluted with water, the gypsum sets after just five minutes and in 30 minutes it completely hardens. Perhaps this is actually the only binder of its kind that does not produce significant shrinkage and can be used in its pure form.
Say what you like, but cement is considered the most durable binder. More high level grades - cement is stronger. M400 is used in solutions. The material hardens in air and water. It sets in 15 minutes, and the process itself can be considered completed no later than one day after pouring water. It becomes completely strong and hard only after half a month.
Clay
Clay is also a binder, but it is used for plastering adobe and wooden walls or in the construction of furnaces.
Fillers
Now it’s the turn of the solution fillers. The most famous is sand. But the highest quality sand is river quartz. Sea water contains a lot of salts, but ravine or mountain water can be mixed with clay. In coarse-fraction sand, the grains are 2/4 mm, in medium-fraction sand - 0.5/2 mm, in fine sand - 0.25/0.5 mm. To carry out work, it will be better if you use medium-grained, less often coarse-grained ones. Use small ones only for covering. The sand for the solution must be clean and free of any impurities. Therefore, before work, it is important to sift it through a sieve with a mesh size of 3/4 mm. If you need a lot of plaster mixture, use an inclined sieve. And if the amount of work is small, then take a regular box sieve.
There are all kinds of mortars: lime, cement, clay and others, more complex in composition. When you make a solution, try to achieve optimal proportions of filler and binder. Such mixtures are called normal.
Cement-sand mortar
To make a cement-sand mortar, we need cement, sand and water. It is recommended to use quarry sand. Once you have chosen your sand, you need to prepare it and remove foreign materials. We use a sieve for sifting. It is best to take a 3x3 mm sieve for a 1.5x1.5 mm cover. To remove clay impurities, it is important to wash the sand. How to check cement for freshness? We take it in our hand and squeeze it: if it flows out, then it is fresh and meets all the parameters indicated on the label. If it begins to clump, then all the basic properties of cement are lost, and more cement will be needed to prepare the solution. This can be determined experimentally.
Cement-lime mortar
Its preparation is almost identical to the preparation of cement mortar. Only, in addition to repeating all the steps, it is still necessary to prepare the lime. Lime is diluted to the consistency of lime milk and filtered through a sieve with 2x2 mm cells. Then, based on lime milk, the solution is mixed and brought to the required consistency by adding water.
Mortar
The preparation of lime mortar has certain specifics. First you need to prepare all the necessary components. Then a certain amount of lime is first added, and then sand is added with gradual stirring. Typically, lime mortar is prepared by using one portion of lime and three portions of sand.
Important ! Test the strength of the mortar: take seven bricks and mortar them together in a column, allowing them to dry. If the mortar holds a pillar of seven bricks, then it is made with high quality.
Clay mortar
How to prepare clay solution? Usually they do this: the clay is soaked until it is completely softened. Then it is filtered through a sieve with 2x2 mm cells, and 2-4 portions of sand are added to this portion, depending on the fat content of the clay.
Lime-gypsum mortar
It is prepared in small portions because it sets within 10-15 minutes. Lime milk is prepared for the solution, and then gypsum is added to the milk. NOTA BENE!!! And this solution must be used within 10 minutes! It can be prepared using special dry mixtures that are diluted with water. For example, this is a simple putty.
The mechanism for preparing various mortars is almost identical, so here is a guide on how to prepare cement-sand plaster mortar. Let's look:
When CaO combines with water, the lime “quenches and turns into calcium oxide hydrate.” The process of slaking lime is accompanied by a large release of heat and the transformation hard pieces into a loose white powder (fluff). As an alkali, slaked lime has the property of decomposing ammonium compounds with the release of ammonia, therefore slurry, when disinfected with slaked lime, loses its fertilizing properties (like nitrogen fertilizer).
Quicklime strongly absorbs water from the air, and to avoid turning it into calcium oxide hydrate, store it quicklime necessary in a dry room. Quicklime or slaked lime, when in dry form (in pieces or powder), does not have a detrimental effect on microbes. The bactericidal effect of lime affects only when mixed with water and is caused by the presence of hydroxyl ions of calcium oxide hydrate in the solution.
Before disinfection, you must first quench the lime and prepare lime milk from it. After 6 hours of preparation, slaked lime becomes unsuitable for disinfection purposes, since the milk of lime absorbs carbon dioxide from the air and turns into chalk, which is ineffective for disinfection.
Preparation of lime milk.
Lime milk must be prepared only from freshly slaked lime. It is extinguished as follows: 200-250 ml is poured into the bottom of a flat-bottomed container (clay or wood). water, and then put in one layer pieces of quicklime in an amount of 1 kg. and, stirring slowly, add water to 1 liter. Pieces of lime heat up very much and crumble into white dry powder (fluff), which is calcium oxide hydrate. To prepare 10% lime milk, you need to dilute 1 kg of slaked lime 9 l. water. Adding one tablespoon of green soap to 1/2 a bucket of lime milk ensures that the lime milk adheres more tightly to the walls.
Lime is a universal material for its purpose. In what niche of construction is it not used! And lime plaster is proof of this! Having learned to work with such a solution, you will learn very big chapter in the repair business.
Lime plaster - what is it good for?
Plaster with lime as a base is used both in interior decoration residential premises, and in the decoration of house facades. Lime owes its popularity largely to its low cost, good adhesion to various surfaces and sufficient reliability. The properties of plaster based on slaked lime have been known for a long time - these are very good fire-resistant properties, thermal insulation properties, high vapor exchange rates, ease of use and elasticity, environmental friendliness, no cracks when driving nails, high antifungal properties.
Covered with lime mortar wooden beams or the partitions will not be sharpened by rodents and beetles. Perhaps the only disadvantage of lime is the fear of moisture, which is why plastering the walls in the bathroom with lime is a rather risky undertaking. However, it is enough to add another component to the lime mortar, which will make it impervious to moisture.
How to prepare lime mortar for plaster without any hassle?
The number of “recipes” for preparing solutions using slaked lime is the same as the number of masters - everyone has their own special recipe, thanks to which a unique composition is obtained. But the basic mixtures are known to every repairman, because they are suitable for a huge range of jobs. Their main difference depends on the additional component with which the lime will subsequently be mixed.
When faced with how to prepare lime mortar for plaster, you definitely need to master the basic, classic recipe- a mixture of lime and sand.
Any type of sand is suitable for our work. Before mixing, you should always take care of its cleanliness - sift and rinse, because without doing this, you will be rewarded with the dubious pleasure of picking out large shells or debris from the ready-made composition. Based on the so-called fat content of lime, one part of this material will require at least two, and at most five parts of sand. You can judge the fat content of the solution by its stickiness - if the mixture sticks to the shovel with which you mix it, then you need to add more sand, but if it doesn’t stick at all, you need to add lime.
To begin with, you should mix less than a third of the required amount of sand and water with lime - this will make it easier to grind all the lumps. Only after this process is completed should the remaining parts of water and sand be added. Quite often at this stage you will come across quicklime pieces - you should definitely get rid of them, as they can swell and lead to the formation of cracks in the wall.
Cement - in combination with this component, a lime-based solution can be used even in damp rooms. Lime-cement mortar is rarely used in the construction and finishing of new premises due to the high cost of cement, but in the repair business it can solve many problems. To prepare it, you will need the same amount of lime paste and cement, and 2-5 times more sand, depending on how strong the solution you want to get. First, mix dry cement and sand, and in a separate container, dilute the lime dough to obtain lime milk - to do this, add the same volume of water to the lime. Pour the milk of lime into the dry cement-sand mixture and stir, adding water to obtain the desired thickness.
Lime plaster is used when a quick-setting composition is required. The lime-gypsum mixture has exactly this quality - it hardens literally within 10 minutes! You need to work with this composition very quickly. It is for this reason that the masters mix small portions, which are immediately put to work.
To stir such a solution, you will need 3-4 parts of ready-made ordinary lime mortar. Divide the solution into two parts, and mix one with 1 part of gypsum. After thoroughly mixing the ingredients, return the second half of the solution to the container and mix again. Use it for 6 minutes, and if you don’t have time, ask your partner to constantly stir the mixture - this will give you a few extra minutes.
The least commonly used is a lime-clay mixture. Clay as a filler is useful only when you need to consolidate a layer of pure clay, since it is not famous for its strength. Much more common in work is a mixture of clay, lime and sand - such a solution is useful when plastering stoves. Of course, the recipe for lime mortars does not end there - in addition to the main components, there are also a lot of minor ones, for example, crushed fiberglass strands or PVA glue are added for strength.
Lime plaster – prepare the composition and plaster the walls!
We have figured out the recipe, all that remains is to master the plastering process itself. For ease of work, the solution should not be too liquid and not too thick - so that a thin layer remains on the spatula that we mix.
How to prepare lime plaster and plaster walls - step by step diagram
Step 1: Prepare the solution
You need to select a different solution for each wall so that the base adheres securely to the layer of plaster. If you need to plaster a concrete or brick surface indoors, both standard lime and lime-cement compositions, as well as lime-gypsum, are best suited. Wooden elements It is better to treat with lime-gypsum mortar. When kneading, use one little trick - add water not in a direct stream, but by passing it through a watering can, so the liquid will flow more evenly, which will make the kneading process easier.
Step 2: Spray the surface
Spray - very important stage, and should not be neglected. This procedure increases the adhesion of subsequent layers to the wall. To spray, you need to make a liquid solution of two parts sand, one part cement and one fifth part lime. Using a trowel, the prepared mortar is applied to the wall in as thin a layer as possible. There is no need to level it.
Step 3: Base coat of plaster
The soil, or base layer, should not be made more than 5 cm thick. A classic lime composition or a complex composition of lime and cement is prepared for it. Experienced craftsmen apply the mortar with a trowel and level it with a trowel; for beginners it will be more convenient to work with one trowel at first. Apply the solution from top to bottom, using wide movements. Excess must be removed using a rule - a special plaster cutter. Be sure to check for evenness both vertically and horizontally.
Step 4: Grinding
This is a finishing thin layer, with which the surface becomes perfectly smooth and uniform. For this, a solution identical to the spray is used. But unlike spraying, a thin layer of grinding is carefully leveled with a special grater. It should be remembered that lime-based is not the most durable material, so before using such a surface, you should give it time to completely harden.
Calcium hydroxide(slaked lime, caustic) - chemical substance with the formula Ca(OH) 2, a strong base. It is a finely crystalline white powder, slightly soluble in water.
Some common names
- Slaked lime- since it is obtained by “quenching” (that is, interaction with water) “quicklime” (calcium oxide).
- Lime milk- a suspension (suspension) formed by mixing excess slaked lime with water. It looks like milk.
- Lime water- a transparent, colorless solution of calcium hydroxide obtained by filtering or settling lime milk.
- Fluffy lime- when quicklime is slaked with a limited amount of water, a white, crumbling, fine-crystalline dusty powder is formed.
Receipt
It is obtained by reacting calcium oxide (quicklime) with water (the process is called “slaking lime”):
C a O + H 2 O → C a (OH) 2 . (\displaystyle (\mathsf (CaO+H_(2)O\rightarrow Ca(OH)_(2))).) C a (OH) 2 → 600 o C C a O + H 2 O. (\displaystyle (\mathsf (Ca(OH)_(2)(\xrightarrow[()](600^(o)C))CaO+H_(2)O)).)Chemical properties
Calcium hydroxide is a fairly strong base, causing the aqueous solution to be highly alkaline.
Like all bases, it reacts with acids; how alkali participates in acid neutralization reactions (see neutralization reaction) with the formation of the corresponding calcium salts, for example:
C a (OH) 2 + H 2 S O 4 → C a S O 4 ↓ + 2 H 2 O. (\displaystyle (\mathsf (Ca(OH)_(2)+H_(2)SO_(4)\rightarrow CaSO_(4)\downarrow +2H_(2)O)).)The neutralization reaction causes the gradual clouding of a solution of calcium hydroxide when standing in air, since calcium hydroxide interacts with carbon dioxide absorbed from the air, like solutions of other strong bases, the same reaction occurs when carbon dioxide is passed through lime water - qualitative analysis reactions on carbon dioxide:
C a (O H) 2 + C O 2 → C a C O 3 ↓ + H 2 O (\displaystyle (\mathsf (Ca(OH)_(2)+CO_(2)\rightarrow CaCO_(3)\downarrow +H_( 2)O)))With further passage of carbon dioxide through lime water, the solution again becomes transparent, since this forms an acidic salt - calcium bicarbonate, which has a higher solubility in water, and when the calcium bicarbonate solution is heated, it again decomposes with the release of carbon dioxide and a carbonate precipitate is formed. calcium:
C a C O 3 + H 2 O + C O 2 ⇄ C a (H C O 3) 2. (\displaystyle (\mathsf (CaCO_(3)+H_(2)O+CO_(2)\rightleftarrows Ca(HCO_(3))_(2))).)Calcium hydroxide reacts with carbon monoxide at a temperature of about 400 °C:
C a (OH) 2 + C O → 400 o C C a C O 3 + H 2. (\displaystyle (\mathsf (Ca(OH)_(2)+CO(\xrightarrow[()](400^(o)C))CaCO_(3)+H_(2))).)Reacts with some salts, but the reaction occurs only if, as a result of the reaction, one of the resulting substances is poorly soluble and precipitates, for example:
C a (OH) 2 + N a 2 S O 3 → C a S O 3 ↓ + 2 N a O H. (\displaystyle (\mathsf (Ca(OH)_(2)+Na_(2)SO_(3)\rightarrow CaSO_(3)\downarrow +2NaOH)).)Application
- Lime milk is used for whitewashing walls, fences, and tree trunks.
- For preparing lime mortar. Slaked lime has been used for masonry construction since ancient times. Such a mortar usually consists by weight of one part slaked lime and three to four parts quartz sand. Add water to the mixture until a thick mass is obtained. In the mixture occurs chemical reaction components to form calcium silicates, in this reaction water is released. This is a disadvantage of such a solution, since in rooms built using such a solution for a long time High humidity remains. This is also why in modern construction cement has almost completely replaced slaked lime as a binder in mortars.
- To prepare silicate
