A brief introduction to dry mortar formulations

In order to more fully understand what dry construction mixtures (DCMs) consist of, how their composition is formed, which components influence what, let’s look directly at the composition of cement itself.

What is cement?

We will not delve too deeply into the chemical processes of both the production of cement itself and, subsequently, the formula components of the polymers and modifiers included in the composition of the cement. So, cement: take 75% limestone (chalk, shell rock, marble) and add 25% clay (shales, loams). Mix this thoroughly using a dry or wet method. The wet method, by the way, is more expensive, but during the mixing process a more uniform, homogeneous mass is obtained, which ultimately affects the quality of the cement. However, this method is more expensive. The dry method has its advantage - it is cheaper. But the clinker mass is somewhat different in terms of uniformity and characteristics than in the previous case.

The resulting mass, mixed in one way or another, is sintered. Thermal sintering technology has certain stages:

1. Drying up to 200 degrees Celsius, removing water;
2. By heating to 650 degrees Celsius, we remove organic matter;
3. Decarbonization 1200 degrees Celsius decomposition of aluminosilicates (refractory thermal elements);
4. Exothermic reaction 1300 degrees Celsius carbide sintering elements;
5. Sintering 1470 degrees Celsius melting clinker minerals;
6. Cooling to 1000 degrees Celsius forms sintered clinker.

The clinker is then ground into a fine powder, to which gypsum is added during the grinding process. Gypsum is required mainly to regulate the setting time. The finer the grind, the more homogeneous the structure, the greater the activity of cement microparticles, the higher the activity of cement. Further, to improve its qualities and performance, to ensure the necessary characteristics, additives are added, which, by the way, reduce its cost. Some components of blast furnace production, roasting products, oxidation or any crushed minerals are used as additives. That is, they are somewhat similar in their characteristics to cement, but their activity is incomparably lower and they serve more as diluents of cement concentrate with minimal loss of its properties, but with a significant increase in volume. That is, the D20 indicator, for example, in PC400D20 indicates that there are 20% additives, and if D0, then it’s as if these additives are not there... well, almost none.

Manufacturers of CCC often take advantage of the fact that they use high-quality cement, for example PC500D0, but do not say what the recipe quantity is. It's clear. And most technologists, under pressure from the economic aspect and competitive cost, lay the minimum allowable amount of this cement. It seems to be highly active, so you can’t put much in the recipe. In fact, cement is a binder. The closer it is to the norm, and the better the norm, the higher the quality of the mixture. The additives in it work better. Therefore, there is no need to look at what kind of cement is used in the mixture: PC500, PC400 D0 or D20. You can take PC500D0 in the recipe, increase its quantity with additives (fly ash, dolomite) and you will end up with PC500D40, which in its essence will be worse and more unpredictable in the mixture than PC400D20 put in the same volume. And it will affect the strength and adhesive properties. But elasticity and softness will be at their best.

We sorted out the cement a little. Cement is the main product in the mixture. Without it there is no mixture. It glues, holds together, and creates plasticity.

Quartz sand

Next we go to quartz sand, i.e. filler. We often see the inscription on the packaging - quartz sand. That is, sand of high homogeneity in chemical composition and a high degree of purification. These are the indicators that are meant by quartz sand. But in fact, the usual so-called construction sand is used in all mixtures, with the exception of some mosaic adhesives and decorative plasters. River, quarry, etc. The deposit, or rather the place of extraction, is selected based on the reduction of losses in the screening of the coarse fraction (coarse fraction), the lowest content of clay and organic inclusions, and, of course, granulometry. The relationship between small and large and vice versa. All. The sand is brought to a processing plant or directly to the manufacturer, where it, the sand, is sieved for roughing. Then it is dried using the temperature firing method, in which all organic matter is removed, then sifted again and only the necessary sand fraction for production is left.

Let's say, based on my enterprise, sand was selected with a sieving size of up to 1.25 mm. Now it is up to the manufacturer to determine how to separate this fraction and obtain the required granulometric sieving. Someone more serious can do, for example, 0-0.3, 0.3-0.7, 0.7-1.25 and then set different percentages for different fractions. Since I rely on my experience, we do 0-0.5, 0.5-1.25. We chose this screening because of the territorial type of sand and its price component, because in the end we had 70% fine and 30% coarse sand. Which was optimal for the bulk of adhesive compositions, but brought its own specifics to masonry and plaster compositions.

The sand is stored in silos, which are naturally cooled and then supplied to the batch (mixer), depending on the recipe glanulometry. In the mixer, cement, sand and polymers are mixed. It is there that the composition of the mixture is formed, which is then supplied for packaging in bags. Cooling is necessary because many polymers are destroyed at a temperature of 60-80 degrees, and in the summer, sand from drying is released into bunkers at 100 degrees.

Granulometry

Now about granulometry. What it is. This is the selection of particles of different sizes so that together they form the most homogeneous mass possible with a minimum of voids. Glanulometry affects many indicators such as strength, adhesion, plasticity, etc. This is a standard, classic approach. Many small factories make mixtures without taking into account the granulometry factor. They put one sieve per fraction, for example 1.25 mm, and then add what they sowed into the mixture.

Very often, and some components are always added to cement with sand, rheological additives are added, such as gypsum, fluff (lime), fly ash (a product of thermal power plant exhaust). By the way, lime is required for all Euro class mixtures. It gives elasticity to cement compositions and increases their crack resistance, but reduces strength properties.

So, by mixing cement and sand in the required proportion, we can already get glue, plaster, masonry mortar or something else. Let's take, for example, 40 kg of cement and 60 kg of sand - glue, 30 kg of cement and 70 kg of sand - plaster, 25 kg of cement and 75 sand - masonry. And so on.

Additive (plasticizer, adhesion enhancer, modifier) ​​cellulose

But. This is not what we need. Let's figure it out further. The cement mixture turns into a durable solution only when it contains water. There is no water, setting stops, resulting in sand and dust. Therefore, if the mixture crumbles in your hands after hardening, then either there is not enough cement, or there are not enough additives that bind the water in it. What kind of supplement is this? It is called a plasticizer, adhesion enhancer, modifier, and everything else. But by and large it is a thickener – paper. Cellulose. But of course, not in the form in which we know it, but processed by industry into a white active powder. There are simple and modified celluloses.

Simple ones are cheaper. They have different viscosity indicators, which are selected for a particular composition. Plasters, for example, and rough floors are made on cellulose with low viscosity. Glue on higher viscosity. Their thickening is higher, adhesive properties and film stability are also high. They are also divided according to the speed of dissolution and the indicator of moisture retention. The rate of thickening or swelling may vary depending on the cellulose modification. Often this determines the time pause between the time of mixing and kneading and re-kneading before starting work. Good manufacturers prefer modified celluloses. Their advantage is that they are additionally modified with elements that actually improve moisture retention, adhesive ability, slip resistance, etc. But even the most modified cellulose remains cellulose, with its main purpose. And to highlight one or another property of the mixture, it is necessary to add the necessary components to the composition. But you can simply rely on cellulose. It's cheaper that way.

There is a certain percentage below which the manufacturer should not add methyl cellulose to their mixture. But the market plays like this - cement is less than cellulose according to the norm, cement is according to the norm and cellulose is at a minimum. In general, that's it. The main thing is to drive the price of the goods into the requirements of the gross market. Methylcellulose, by the way, is often the most expensive element per volume of dry mixture.

Expensive adhesives, where the price tag is serious, are made taking into account the recommendations of polymer manufacturers. It is not customary for them to deviate from instructions. It is said that for adhesive for interior work on non-deformed bases, 200 kg of cement requires 2 kg of cellulose, then it will be so. And with us they will make 200/1, at best. Why is this dangerous? For a well-prepared base and normal humidity and temperature - basically nothing. Well, of course, if a finisher with a water-solid attitude doesn’t make a mistake. It will be more difficult to work, and the thixatropy is conditional. But if it’s hot or the base absorbs water strongly, and you save on priming, ... we get adhesion 0.2 instead of 0.5 and grade 50 instead of the stated 150. And it’s not a fact that the glue is bad. It simply does not tolerate deviations from ideal use. Not at all. But there are always deviations. Always. This means the error rate is higher. The worst thing is when these percentages are used on building and load-bearing materials that strongly absorb water - cellular concrete of any kind. There the walls can collapse from the wind. And the houses are folded into boxes. I personally observed it. And if an already built house is shaken by a weak earthquake, then we will get a sandbox made of cubes.

Concluding about cellulose, you can give several recipes because... We have reached a normal complex of components of simple recipes. Plaster cement 200-280 kg of cement, 800-720 kg of coarse sand, and cellulose 1 kg. We will get a grade of 100-150 (10-15 MPa) and adhesion to the base of the order of 0.5 MPa, even a little higher. By the way, why not a masonry compound for building bricks? Glue. For tiles. For interior work. Cement 340-400 kg, fine sand 658 - 598 kg, methyl cellulose 2 kg. We get grade 150 (15 MPa) and adhesion of about 1 MPa. True, there is no thixatropy - there is a decent amount of slippage, but when laid from bottom to top there are no problems. These are pure recipes, let’s say.

And we can make glue like this. Cement 340 kg, Sand 640 kg, Lime (fluff) 10 kg (thickened, softened), fly ash 7 kg (added greater softness, increased homogeneity), methyl cellulose 2 kg. And we get a relatively thixatropic, elastic glue with adhesion of 0.5 MPa and grade 150 (15 MPa), but installation is also only from the bottom up. We are missing something.

RPP – redispersible powder

Let's move on to the next important component - the polymer modifier. RPP – redispersible powder. What it is? Very simply - take acrylic mass or just acrylic-based paint, dilute it with water. And then we spray it through the nozzle, but during the spraying process we remove all the water. What remains is a powder, which when combined with water becomes a homogeneous elastic mass. After this mass hardens with water, the reaction no longer occurs. If this powder is added to a cement-sand mixture, it will bind particles of hydrated cement and sand with an elastic ligament, long or short, with certain properties. This will give the cement mixture certain properties. RPP manufacturers additionally modify their products with various compounds that create the desired properties for the final product.

There are two important indicators here: the film formation temperature and the glass transition temperature. The first is the higher temperature, which creates a stable polymer film. If the polymer is dried at a temperature lower than stated, then there will be no stable film, cracks will form and there will be inhomogeneity. And the glass transition temperature is the temperature at which the elastic film of the polymer becomes brittle. But it is not directly dependent on the specified temperature, since it is already in conjunction with the solution and supported by the binder and methylcellulose. But all the same, the lower the glass transition temperature, the better the resistance to cyclical temperature changes.

By and large, that's all. This is the necessary volume of elements to create almost any product that we need.

Now the chemical industry offers various additional additives: shrinkage compensators, superplasticizers, antifoaming agents, blowing agents, thickeners, etc. All these components have already been calculated quantitatively for mixtures, and these indicators are included in the recommendations for their use. By the way, to impart high thixatropy properties and increased resistance to slipping, you do not need to take a specialized RPP, but rather add, say, starch ester into the mixture, which will be cheaper than a specialized RPP and better. Although RPP manufacturers may argue with this. Marketing.

Winter mixtures

I'll add more. Winter mixtures. In the Northern regions, facade work, construction and finishing work in unheated rooms do not stop even at -20 degrees. And builders also want to work with mixtures at this time, because it is convenient. But the cement mixture at temperatures below 5 degrees already begins to behave not standardly, but at 0 degrees and in general can catastrophically reduce the open time. There is a way out - for example, the food additive E238. A preservative for food products called calcium formate, and for cement mortars calcium formate. This additive in varying concentrations to the dry mixture serves as a setting accelerator, anti-frost additive, and strength enhancer. By adding this modifier to the mixture, we can lower the temperature of use of the mixture, guaranteed to -10 degrees, and with special recommendations for use to -15 degrees. In the conditions of the Southern regions with mild winters, it is possible to maintain the production of facade work for the entire winter period.

All. Then positioning in the market, price niche, profit margin, etc. play a role. Net brand sales.

Conclusion

I’ll touch a little on polymer manufacturers. There are factories located in Europe. They make a quality product, but in limited quantities. Their production cannot fully cover all production on the Eurasian continent. Therefore, they often compensate for the lack of their products with gross product from China. He's no worse. Sometimes it is even better if you compare, for example, the delivery of a product at the end of its expiration date from Europe and a fresh product from China. But still, quality control in Europe is higher. And it is European polymers in European mixtures that work as they should. But, for example, European manufacturers are already setting up their factories in Siberia. Should we bring polymers there from Europe? And the quality of the European brand in the Trans-Ural region is already close to that of local producers. Well, it differs, of course, in terms of prescription and control standards, but still there is a difference.

Let's touch a little on the production of products for another brand. For example, some large chain orders a line of mixtures under its brand. One can, of course, argue that they choose the best formulations at reasonable prices, negotiate on volume, thereby further reducing the manufacturer’s profit percentage, etc. But in fact, you can remember the cartoon about how a gentleman brought a sheep skin to the market and asked him to sew a hat for him. How about two? How about three? Can you do four? And so on. It’s the same here - you need such and such a product at a price no higher than that, with such and such characteristics. Well, you yourself understand what we get.

By the way, advice on how to calculate the price. In a normal glue, the cement in the bag should be at least 30% (estimate the price of cement on the market and do the math), polymer, no less than 15 rubles, packaging and logistics will cost 20 rubles, sand is 50 kopecks per kilogram, because it dries , is sown. So let's estimate: cement 25/100*30*4.5=33.75 rubles, polymer 15 rubles, packaging and logistics 20 rubles, sand 8.75 rubles. We get 77.5 rubles. We add 50% for production costs and at least 10% for profit. We end up with 127.87 rubles per 25 kg. This is the minimum price of normal simple glue for any local manufacturer. But this is just for fun.

The article is based on the following materials:
Speech by the commercial director of Maska LLC, R.G. Vinnikov.