How to prepare a mortar for plastering walls
The mixtures used today in construction are created by the rational selection of binders, fractional aggregates and water. Mortar for wall plastering differs from concrete in the absence of large aggregates in its composition, but in basic properties and characteristics they are largely similar - in any case, when it comes to cement mortars.
This manual will provide you with comprehensive information on many issues regarding plaster mixes. You will learn what mortar to plaster the walls with, how to make it, what the mortar consumption for 1 m2 of plaster should be. And to fix the received material, the video in this article will help you.
The content of the article
Varieties of plaster mortars
The classification characteristics of all mortars are based on such indicators as a type of cementitious component, bulk density (weight 1m3), as well as their physical and mechanical properties. Since there are no various large aggregates in stucco mixtures, as in concrete, they belong to the category of light solutions.
As for the binder, then the plaster is just the same variety. The thing is that for their manufacture they use not only cements, but also gypsum, clay, lime. The last two options are introduced into the compositions as a partial replacement of the main binder. Only gypsum and cement do not mix with each other.
Why do the components vary?
The composition of the mortar for plastering the walls is adjusted in order to give it higher ductility or water resistance. Of great importance is the fact that the price of the finished product is reduced, and this, in turn, can significantly reduce the cost of finishing work.
- Clay-cement, lime-cement, lime-gypsum mortars are called mixed, and each of them has its own purpose, and its own rate of mortar for plaster. In addition to organic substances, synthetic additives are introduced into some formulations. For example, the mixture that you see in the photo below, containing polymer fiber in its composition, can be used for both indoor and outdoor use.
- Lime gives the solution plasticity, fiber reinforces the screed, which increases its strength. In general, one or another version of the solution is selected based on the operating conditions of the room, or the building as a whole, because the walls are plastered not only in houses and apartments, but also in production shops, public and administrative institutions.
- And then, plaster mortar can be used not only as a finishing material. Plastering is an effective waterproofing option for both brick and masonry, and for concrete surfaces, and is performed not only on surfaces of ground structures, but also on foundations.
- There are many other types of solutions that are resistant to chemicals, high or low temperatures. Therefore, plaster mortars are divided into finishing, which, in turn, are divided into leveling and decorative, and special, having a fairly narrow scope.
Since the topic of our article is the preparation of mortar for plastering walls, we will not talk about special options here. The basis of the characteristics of any solution, including the finishing one, is the strength of the screed. For facade options, along with strength, frost resistance is also crucial.
Stucco preparation
Plaster mixes, as well as concrete, must withstand certain compressive loads. This indicator is expressed in the brand, the digital designation of which means the number of kilograms per square centimeter of screed.
Note! Changing the dosage of a component, changes the characteristics of the solution, which means that to obtain two batches with the same properties, it is necessary to observe the exact dosage. Therefore, before preparing a solution for plastering walls, it is necessary to stock up containers of a certain volume, which can be used as measuring dishes, although on mortar-concrete units, sand, cement and other additives are simply weighed.
Grades of plaster mixes for walls
Those who are going to master the technology of plastering, and, accordingly, prepare a solution with their own hands, you need to keep in mind this. The brand of mortar for plastering the bearing walls should have a strength index of 100 kg / cm2, and is indicated by M100. Lime in such solutions is either not added at all or introduced, but in very small quantities.
- But in the manufacture of solutions: both cement and gypsum (see Gypsum plaster: use technology), intended for internal work, lime can and should be used, since it significantly improves the properties of plaster. Lime dough not only increases the plasticity of the composition, but also reduces the consumption of plaster mortar per m2 of wall. We will say more about how to make such a solution, but for now we will return to the brands.
- Whatever additives are introduced into the plaster mixture, according to its characteristics, it must meet the requirements of its brand. If M100 grade mortar is required for load-bearing walls, then M50 strength is sufficient for internal walls and partitions.
- We note immediately that this applies only to the leveling layers of the plaster coating: spray and soil. With reference to dry compositions of factory preparation, such a brand have basic (starting) mixtures. Thin layer plaster coating layers finishing putties and decorative plasters, it is enough to have the strength of M25.
Therefore, before you prepare a solution for wall plastering, you need to familiarize yourself with its properties, recipes and preparation rules - and we think that we can help you with this.
Properties of solutions and recommendations for their manufacture
If the components of the solution are not weighed, but dosed by volume, it must be borne in mind that there is such an indicator as bulk density. It depends on two nuances: particle size and humidity.
To a greater extent this applies to binders, since they have the finest dispersion. If two identical containers are filled with cement: one is packed, and the other is normal, then the first vessel will be heavier.
- There is one more crucial moment. Unfractionated as well as non-sieved sands react very strongly to changes in relative humidity in the environment. The bad news is that their bulk density is changing, so it also happens unevenly, which cannot but affect the final result.
Note! The use of whole sand can result in the following: the dosing of the components in two different mixtures seems to be the same, but the compressive strength of the solutions turned out to be different. More often this leads to the formation of cracks on the screed, and sometimes it can even violate the integrity of the base.So, the quality of the sand used to make the plasters is crucial.
- In the manufacture of plasters, builders adhere to this rule: the volume of the finished solution should correspond to the total volume of dry components. This may seem strange to many, since water is still added to them. But this is understandable: in the dry state, the filler particles adhere closely to each other, and after mixing, they disperse, and the density of the mixture decreases.
- In the formulations of simple solutions, in the composition of which there are no mineral additives at all, the proportions of the components are indicated as the ratio of a certain amount of volume or weight parts to one part of the binder. Since in such compositions there are only two bulk ingredients, the proportion is indicated by two numbers - for example: 1: 5.
- In those solutions where there are two binders, or there are additives of mineral origin, the ratio of the components is indicated by three numbers. The first is always cement or gypsum, the third is sand, but the additive is between them. A similar proportion looks like this: 1: 0.5: 4.
In the manufacture of mortars at plaster stations, active organic additives based on soap-oil or sulfide-alcohol stillage are introduced into their composition. They allow you to reduce the consumption of binder, and increase the plasticity of the finished mixture, which is most important during machine application.
At home, as an additive, you can use the well-known PVA glue, at the rate of 100ml / 10l solution.
The mobility of the finished solution
Workability - that is, the ability to distribute on the base with minimal effort, is the most significant quality of the finished plaster. But this property depends on its ability to retain water, on which the mobility of the mixture depends in the first place. The moisture content in the solution, as well as the dry components, is accurately dosed, and should not exceed the limit after which the mixture is delaminated.
In simple cement mortars, this limit is determined by the cement-water ratio. For different types of plaster, the water content varies between 30 - 50% of the total volume of the solution. To increase its water-holding ability, just fine mineral active additives are added in the form of lime or clay.
When using such additives, for the manufacture of cement mortar, you need to use only dry sand. Where there is no cement - for example, in lime plaster, this filler may have natural moisture. The fraction of sand in the manual manufacture of plaster should not exceed 2.5 mm for leveling layers, and 1.2 for the finish.
Recipes for some solutions
All types of solutions mentioned above can be bought in the form of a dry mixture, which can only be diluted with water. But many people prefer to cook them on their own, although for various reasons: someone does not like the cost, someone has delivery problems. We suggest that you familiarize yourself with the formulation of the most popular types of mortar used in low-rise construction.
Gypsum-gypsum plaster
This type of mortar is best suited for leveling walls inside residential premises. Its main advantage in this case is the white texture, which greatly facilitates the process of finishing.
So:
- We note immediately that lime-gypsum solutions should be used only in those rooms whose humidity does not exceed 60%. For outdoor work, they can be used only in regions with a dry climate, but in our country there are none, in general, no.
- Such plaster consists of gypsum dough and lime mortar - they are prepared separately, and then combined.Plaster dough of normal density, mixed in a proportion of 1.5 kg of plaster per 1 liter of water. As for the lime dough, you can buy it ready-made, or cook it yourself.
- Only this must be done in advance, since it takes a day and a half to extinguish the lime, and the solution still needs to be allowed to stand for a couple of weeks. For this purpose, hydrated lump lime is used, which must be wiped through a metal sieve before soaking in water. If necessary, a detailed description of this process can be found on the Internet without any problems.
Proportions of lime, gypsum and sand, for different layers of plaster coating:
- Spray - 1: 0.3: 3
- Soil - 1: 0.5: 2
- Nakryvochny - 1: 1: 1
Sand is added to mortar - It does not harden for a long time, so there is nothing to worry about if you made it ahead of time. Everyone knows that gypsum mixtures instantly set, therefore, after gypsum dough is added to lime, you only need to think about how to quickly develop a solution. Therefore, you need to mix it in small portions.
Cement Mortar
Cement plaster used mainly for plastering facades, basements, socles, as well as rooms with wet or wet operation. You can prepare a solution of a certain brand in different ways, and it depends on the brand of cement used.
Thus, if we take cement M400, then in order to get a solution of M50, you need to adhere to a ratio of 1: 6. With M300 cement, the ratio changes to 1: 4.5, but if you use M200 cement, the sand content in the solution will be even lower: 1: 3. For nakryvochnyh layers, in which, as already mentioned, the plaster can be no higher than the strength of M25, use only cement M200, in the ratio with sand 1: 6.
In the manufacture of cement mortar, each master determines the procedure himself. Some put cement in the water, mix it with a mixer, after which sand is gradually added. But ideally, it is better to first combine the dry ingredients, pass them through a sieve so that the lumps break, and then, thoroughly mixing, add water.
