Dry plaster cement-lime-sand mixes: we consider in detail the compositions

Gusevsky Andrey Anatolyevich

Sand cement mixture

Sand-cement mixture for plaster is used most often. This is a traditional composition that can suit most parameters. But sometimes the characteristics of the coating are changed with the help of additives and in the modern world there are quite a lot of them.

Today we’ll talk not just how to make a cement-sand plaster mix, but also consider additives that can be used. You can also watch the video in this article and photos that will help you make the most optimal choice.

Stucco: interior and exterior works

The cement-sand plaster mix is ​​made in only two main types, the first for interior work, and the second for facade, it all depends on the conditions in which it will be used in the future.

• When choosing facade plaster, priority should be given to one that has passed the test of strength and durability. Since the surface of the building on which the plaster was applied endlessly contacts the external environment, the facade plaster must be resistant to moisture, withstand frost, and not be influenced by ultraviolet radiation and atmospheric oxygen.
• When choosing facade plaster, you should also consider the material from which the walls of a building are made. In order to avoid cracks or delamination by pieces of plaster, for those houses whose walls are finished with cell concrete, air bricks and in which there is a significant void, it is not necessary to use ordinary mixtures of cement and lime.
• The modern market is filled with offers of special mixtures with a gentle composition, most of which have a gypsum base with certain additives. The best option would be to consult with knowledgeable people, to find out the opinions of masters, they will easily tell you the most suitable material for the walls of the house that you want to plaster.
• When choosing plasters for internal work, it should be remembered that it is practically not exposed to weather conditions, so emphasis should be placed on environmental friendliness, in this case the plaster is water-based. And even if there is an insignificant content of polymers somewhere, this will not do any harm, since they do not emit toxic substances upon decomposition.
• Decorative qualities also play a significant role in choosing the type of plaster, however, it should be noted that the division into types has a somewhat arbitrary sign, because many plasters have a universal structure, so that they can be used both for interior and exterior decoration.

Cement plaster and its advantages

Cement-sand mixture plaster It has a number of advantages over other coating options.

Let's get to know them better:

• Low price - due to which, its use is so popular among the layman.
• Very large rangeaccessible to any person. You can also purchase a ready-made mixture in bags weighing from 1 to 30 kg, or order a ready-made solution from 1.25 to 5 m3 directly at the factory.
• Comfort in use. After the solution has already been applied, it remains very plastic for several hours, this allows you to further smooth the surface once.It is enough just to wet a freshly plastered surface with water in order to grind it again.

Cement plaster and its cons

So:

• The thicker the layer deposited, the greater the possibility of cracking, slag Portland cement and Portland cement showed themselves as shrinkage, this is the underlying reason for their occurrence. In order to avoid an overabundance in thickness, the layer should be 1-3 cm. The larger the sand fraction, the less even the surface will be, the less chance of cracking, but the durable surface properties also decrease.
• Very poorly applied cement-based plaster. This is typical of all houses in the floors and walls of which there is concrete and metal formwork, as well as for panel houses and houses made of reinforced concrete.
• Extremely low working productivity. Even the most skilled craftsman is not able to make more than 7-10 m2 of plastered surface within eight hours of working time.
• There are difficulties during the execution of work. Despite the fact that even in the Soviet Union mainly women were engaged in plastering, as well as laying asphalt, this does not negate the burden of doing this work, now, thanks to the emancipation of women, they were relieved of such enormous loads.
• Wet process. Work with cement mortar can be considered with full confidence as dirty and wet. When performing, you should avoid applying this solution to any wood surface, including avoiding contact with windows and doors if they have wood parts. But often in such places and such a plaster finds its application.

Caution: Before starting work, it is necessary to insulate the wood parts of the surfaces in places likely to come into contact with the solution. Such precautions are necessary so that wooden surfaces, in particular windows and doors, after they are saturated with water from the mortar and completely dry, do not change their original appearance: there are no distortions or swellings, which is fraught with the fact that the windows and doors will cease to function properly least - will not be closed.

• Not the highest environmental friendliness. Despite the fact that since the beginning of the 90s environmental workers began to propagate about the harmfulness of cement to humans, people continue to use it, due to the fact that no one has yet found a worthy replacement for “harmful” material.

Features of the use of cement compositions

A cement-sand plaster mix contains cement as a bonding element, and it always reacts to changes in temperature and air atmosphere, after applying it to the surface, it always “sits” a little.

In order to avoid various unpleasant factors, special attention should be paid to the careful preparation of the solution:

• Sand is often used as a filler, sometimes it is replaced with crushed lime.
• If sand of various fractions will be used in the solution, then it can rightfully be considered better.
• If it is not correct to work with already prepared cement mortar, this can provoke the appearance of cracks in the plaster (see Sealing cracks in plaster: how to do it right) If the solution dries in the natural environment familiar to it for exactly a month, then only after this time it will become absolutely durable and unscathed.
• It is worth focusing on the fact that there are surfaces with a roughness, such as silicate brick, foam concrete, which absorb moisture very much from the plaster applied to them, and this is fraught with a violation of the strength of the coating.

Caution: To avoid this, the walls and ceiling should be pre-coated with a special primer. And with a layer of more than two cm, it is imperative to use a building grid as a coating.Which greatly enhances the adhesion of surfaces and does not crack.

• If you try to speed up the drying time of the plaster using stoves, hair dryers or fans for this, this can also cause cracks.
• It is also possible to dry in places and accelerate subsidence. When working with plaster in basements, garages and similar premises, one should not forget that plaster has the property of passing moist air vapor through itself from the inside of the building to the outside. That is why when choosing a ready-made mixture, you should take into account all the directions, recommendations and tips printed on the product packaging itself and not violate the proportions of the use of plaster indicated there.
• After the walls of the room have been leveled with a solution, you should not immediately proceed to the next finish, but rather wait a certain period of time, often 10-15 days is enough.
• It all depends on what thickness of the coating layer and also takes into account the humidity and temperature in the room, and the wait time depends on this. But if it is very necessary to reduce the repair time, then it is best to use gypsum-based plaster in the work (see Gypsum plaster: use technology).

Gypsum additives

If we compare gypsum and cement mortar, then gypsum has priority in the speed of drying and hardening, this is due to the fact that the basis of the gypsum mortar filler is sand of fine fractions. Gypsum dries in a few hours.

Cement-gypsum composition

Caution: Gypsum is used as an additive if you need a smooth surface that dries quickly.

• Cement-gypsum mixture is most preferred when working with ceilings, since gypsum mortar interacts very well with many surfaces.
• Since gypsum mortar has extremely low thermal conductivity, the plaster from it is nothing but an excellent heat insulator.
• In rooms where microclimate support is needed, the ability of gypsum to absorb excess moisture will come in handy very well, and subsequently begin to give it away.
• If the bathroom has quite excellent ventilation, then only in this case can cement-gypsum plaster be used, in other cases if air humidity of more than 60% gypsum plaster is extremely undesirable.
• Cement-gypsum plaster was popular and demanded among consumers by comfort in work and an economical component.

Since gypsum-cement plaster requires quick consumption, the mixture dries quickly, so never do it in large quantities. Especially if you do not have the necessary skills.

Applied additives

Plaster cement-sand mixture may have other additives that will change the characteristics of the mixture. In most cases, the presence of various additives in the solution is a mandatory factor, despite the fact that their content is approximately 1.5% of the total volume. Why should they be present without fail?

Because their presence plays a very important role and has a significant impact on improving the various characteristics of mortars, both chemical-physical and typically working.

Namely:

• Longer service life;
• The coating is much stronger;
• The appearance of the fungus is coming to naught;
• The performance of finishing work increases significantly;
• Repair costs are reduced;
• Humidity is kept in cement mortar;
• The quality of work is greatly improved;
• A bunch with different surfaces is significantly strengthened;

However, this is not the entire list of auxiliary properties of various additives. It should not be surprising that manufacturers often simply do not indicate the presence of any additives, but the basic information about under what conditions and in which premises you can use this or that mixture can always be found on the box of the finished mixture.

Mistakes in the preparation of cement-sand mixture

Often, during the preparation of cement plaster with your own hands, you can inadvertently add an excessive amount of liquid. It is extremely undesirable to do this, if at the output you do not want to get a poor-quality layer of plaster, it will start to stick together worse and increase shrinkage.Therefore, thoroughly study the instructions before starting such work.

Caution: You should pay attention to how the solution should look, which is prepared correctly. It should not contain any lumps and should have the appearance of a uniform consistency.

• The first thing you need to start with is to prepare the optimal amount of water, which is indicated in the instructions, after which carefully mixing, you need to slowly add the mixture itself. Stirring is best done using a drill with a special nozzle designed specifically for this purpose. It should not be forgotten that the rotation speed of this drill should not exceed the threshold of 800 rpm, otherwise there is a risk of delamination of the dried plaster, light fractions will rise up, and heavy fractions will lie on the bottom.
• You need to wait at least five minutes in order for the additives that are in the solution to connect to the base, after which you can mix everything again. Now the solution can be considered properly prepared and you can begin to work.
• To throw the solution on the base, it is recommended to resort to using special tools. If the solution is lacking somewhere - it should be added, if its excess is observed somewhere - you need to carefully remove it. Then the surface must be thoroughly leveled so that there is no dirt, roughness or other roughness left on it.
• One of the mistakes made by novice workers - if the solution begins to thicken due to hot weather, they add water to it. It’s better not to do that. You just need to take a tool, such as a shovel or drill, and mix the entire mixture again thoroughly.
• There is also a common misconception, the meaning of which is - the more cement is added, the stronger the plaster. Indeed, with an increase in the amount of cement, the coating becomes more durable, however, after drying, the layer contracts, which causes the appearance of cracks.
• The stucco layer simply should not be stronger than the base, because it begins to react very sharply to temperature changes, which provokes the appearance of compressions and expansions.
• Plaster is applied not only using the manual method, but also machine. The machine method, in comparison with the manual method, rapidly increases the coating productivity by several times, by about five times.

When choosing a ready-made mixture, you should pay attention to the composition, brand of strength, cost and volume of packaging.

Purpose:

• For use in dry rooms;
• For internal or external work;
• For use exclusively on concrete, brick or aerated concrete walls (see Stucco for aerated concrete: how to do according to the rules);
• For single-layer application of plaster;
• For carrying out restoration work;
• For use with mechanized plastering;

In addition to cement and gypsum, the composition of the finished mixture may contain other ingredients: mineral and chemical additives, perlite, lime, polymer modifiers and sand of various fractions.

• Strength grade can range from two to seven Mega Pascal.
• The consumption of the dry mixture can vary from 0.7 to 2 kg, if you take 1 kg per 1 square meter and a coating thickness of 1 mm as a calculation.
• The volume of packaging can vary from 5 to 50 kg.
• The cost already depends on the allocated amount for the cost of the product and its quality.

Dry cement-lime-sand plaster mixes are available in retail, but if you do it yourself, then the price will be much lower. The instruction will help you not to make mistakes.