Polymer -cement mortar is one of the modifications of a conventional sand-cement mortar. Also, polymers can be added to mixtures, which are used when laying plaster and other facing material. Adding this substance to the composition helps to improve its characteristics.
General Description and Difference
A cement mortar from ordinary constituents, like other mortars in which a mineral substance acts as a binder, has a number of disadvantages. Among them, low tensile or bending strength, low impact resistance, low percentage of deformation, low abrasion resistance and poor adhesion with respect to other building materials stand out especially. The list of disadvantages is quite large, which greatly limits the use of a conventional solution. In order to reduce the influence of these deficiencies as much as possible or completely eliminate their influence, special polymers are introduced into the mixture as an additive from 2 to 30% of the total mass. Thus, we can say that the composition of the polymer-cement solution differs from the usual only in the presence of this same additive.
The introduction of the polymer in the mixture
It is worth saying that the polymer, one way or another, is introduced into a large number of very different mixtures. Most often it is intended only to improve plasticization, as well as hydrophobization. In addition, the presence of such additives is less than 1% of the total mass. This is the main difference from a full polymer cement solution. In them, the polymer seriously affects the composition, changing its physicochemical properties, its structure, and also enters the solution as an independent element, and not as an ordinary additive.
Polymer addition methods may vary. For example, you can add it in the form of an aqueous mixture. In such cases, usually its content in cement will be no more than 3-5% of the total mass. Much more often, a method is used in which aqueous dispersions containing polymers are involved. The difference is that in the dispersion the polymer does not dissolve in water, which means that its amount can be increased. Thus, it is possible to introduce into the cement mixture about 10-20% of the additive of the total cement mass.
Additional items
It is worth noting that all the characteristics of the polymer-cement solution may be lost if during the addition of the polymer dispersion a process such as coagulation or curing of the solution occurs. Most often, in order to avoid such negative consequences, various stabilizers are used. As them usually choose surface-active substances (surfactants) - OP-7 or OP-Yu. It is also possible to replace them with a small group of electrolytes, for example, liquid glass. Only a polymer-cement solution, which was mixed on the basis of a plasticized dispersion of PVA, can do without the addition of a stabilizer.
However, the introduction of surfactants does not pass without a trace. Most often, these substances act as powerful blowing agents, and they are also able to draw air into the mortar mixture. If this happens, the smallest air bubbles that have been involved can reach 30% of the total mass of the solution.
Change solution properties
The presence of polymer additives in the solution helps to more evenly distribute the pores, as well as to make their volume much smaller. You can give an example. In a conventional cement mortar, for example, pores can be up to 1 mm in diameter, and their main part differs by 0.2-0.5 mm in volume. If we are talking about the polymer-cement composition, then the maximum volume is reduced to 0.5 mm, and the largest amount, about 90-95%, will not be more than 0.2 mm at all.
This speaks in the most positive way, for example, when the plastering of walls is completely leveled with a polymer-cement mortar, where the pores could disrupt the general structure. It is also worth adding here that those mixtures in which there is air involved are characterized by greater ductility, as well as better workability with a lower liquid content. As mentioned earlier, plasticization of such compounds is also at a higher level. All this leads to the fact that when adding water it is very important to take into account the percentage of air involved and the plasticization of the polymer-cement mortar.
Adhesive properties
Such compositions exhibit increased adhesion, which is explained as follows. When applying the mixture, the polymer is concentrated at the interface and plays the role of an adhesive base between the solution and the base. As for the adhesion itself, it directly depends on the type of polymer added, as well as on its concentration. Further, it is worth mentioning that this property manifests itself only when the solution is dried in air-dry conditions. Therefore, for example, a plaster with a polymer-cement mortar, applied to the walls, will be an excellent basis for laying. If curing occurs in water, then adhesion will not perform so well, even with a huge concentration of polymer. This is due to the fact that stabilizers dissolve in water, and some additives are even able to change their properties if they are in a liquid medium.
We can add that a high level of adhesion affects not only improved adhesion to other materials, but also the mechanical characteristics of the solution itself. This is especially noticeable when stresses arise in tension and bending. In mixtures with additives, these indicators are about 10 times higher than in conventional ones. This is due to the fact that the polymer layers bind mineral components to each other. There is also such a characteristic as the modulus of elasticity, which is about 10 times lower than that of a conventional one. Due to this fact, we can safely say that the polymer composition is more deformative than ordinary.
Shrinkage and other characteristics
If more than 7-10% of the polymer of the total cement mass is introduced into the mixture, then during its solidification more significant shrinkage will be observed. However, since at the same time the deformability of the solution also increases significantly, the mixture is not inferior to the usual in such characteristics as crack resistance, and in some situations it can even exceed. Another difference in the parameters is the return of moisture. In a polymer solution, it passes more slowly, which positively affects the hardening process, since there is no rapid drying, which can cause cracks.
Interaction with other materials
What is a polymer cement solution used for? All of the above properties and characteristics of the material have led to the fact that it is excellent for fixing cladding materials, as it can provide better fastening. Here you can give a simple comparison of the usual mixture and the mixture with the addition of polymer. A solution based on cement and sand creates the maximum fastening strength to 7-9 days after lining, and by 28 days this figure will decrease by about 5-6 times. If we are talking about a solution with an additive made of polymers, then the maximum fastening strength will be achieved a little later, by 9-10 days, however, its absence in the future is not observed at all. Due to this quality, such compositions have become widely used in lining.
The best compositions for work and consumption
When modifying a conventional cement-sand mortar with plasticizers and polymers, a significant reduction in consumption can be achieved. Polymer-cement mortar can be applied as thin as possible and at the same time be a quality base for the facing material. This is due to the fact that dispersion with polymers not only seriously increases ductility, but also involves air from 8 to 12%.
To date, the most promising solution in this area is considered to be one that is made on the basis of a gypsum-cement-pozzolanic binder (HCPV), as well as aqueous dispersions of polymers. It is possible to use such a composition both during external works and with internal plastering. However, the greatest effect, as practice has shown, is achieved when applied in decorative solutions and mastic mixtures for processing building facades.
Composition Requirements
To date, there is a state document that regulates all the requirements that must be observed when operating this kind of mixture. Previously, for a polymer-cement solution, GOST 28013-98 was not fully prepared. Its effect was extended only to ordinary mortar, without special additives. Instead of this and incomplete GOST, SP 82-101-98 was introduced, which extended to a more complete list of all mixtures. For example, the set of rules states that special mixtures can be prepared only in special units - in mortar plants, if they are used in the construction of public buildings. In addition, only special dump trucks or mortar trucks should be used to deliver such building material. Another important requirement was that all the constituent components, before proceeding to their mixing, must pass all the necessary tests for their suitability and quality.
Composition for flooring
The most significant difference between a conventional solution with the addition of polymers from that which should be used for flooring is that it has a higher abrasion resistance and does not form dust during wear. Most often, PVA dispersions or styrene-butadiene latexes are used to formulate such a base. If you add latex in an amount of 15-20%, then you can increase the abrasion resistance by 4-5 times, if you add the same amount of PVA dispersion, you can achieve an increase in this parameter only 3 times.
If we conclude from all of the above, then we can say with confidence that the use of the usual mixture is no longer so relevant. The presence of a variety of additives is justified, even if it slightly increases the cost of the mixture.