Dry mixes for floor screed

When repairing an apartment or private home, often the least attention is paid to the floor, although its quality is largely determinant of the comfort of living in the room. After all, the surface of the floor should be durable and perfectly flat. Using a special mixture for floor screed, you can easily achieve this effect. However, as in the choice of any construction material, the question of optimum quality, manufacturer’s warranty and, of course, the price of the goods is crucial. First of all, when choosing mixtures for screeding, it is necessary to determine approximately the thickness of the required layer of mortar. Most manufacturers make mixes that maintain the height of the screed at the level of 20 to 40 mm. That is, they guarantee that if the floor is filled with properly prepared mortar at this level, there will not be any cracks even over time. Determine how uneven the floor in its original state can be using a liquid level, comparing its readings in different corners of the apartment. If the maximum difference between such readings was 30 mm, then in order to make the surface perfectly flat throughout the room, you will need to choose mixes that support this difference, for example, supporting a layer of 10 to 50 mm.

Using rough mixes

In most dry mixes, the binder is cement. Other powder-type materials are added to it for additional strength. And it is from these additives depend on properties such as full hardening time, adhesion to the substrate and impact resistance – resistance to mechanical stress. As when working with walls – plastering or puttying, among dry mixes you can distinguish those that are designed for roughing and finishing work. Roughing mixes are often used when the required layer is more than 60 mm. In this case, when preparing the mortar, additional reinforcing elements should be added to it. Such aggregates may be granite rubble, expanded clay or similar material, up to half of the layer thickness. The use of crushed stone in the ready mix will not only provide considerable savings, but will also guarantee that no shrinkage cracks will occur. In this case, you can add it in an amount of up to 50% in relation to the ready mix. Thus, if there is a need to do screed floor thickness of 50 mm or more, it is better to use a mixture for screed rough type, cheaper to purchase. The composition of such mixes is mainly sand and cement + a small percentage of impurities. However, in the case if the quality of the floor in the apartment is initially good, then the best choice will undoubtedly be the purchase of self-levelling mixtures, which, although they are in a slightly different price category, but allow you to work with a lower layer height screed. In such mixes the fraction of sand is much smaller, so the finished mortar is more fluid, which has a positive effect on the final quality.

Fast-curing finishing dry mixes

Another factor influencing the choice of dry mix is the urgency of work. Sometimes time is more important than money, and there is no opportunity to stop the construction work for 24 hours for complete curing of the mortar on the floor. In such cases there are quick-curing mixes, which, it should be noted, are in a more expensive price category. Pouring screed with such mortars, you can not actually stop the other work, because the time of complete curing (until the possibility of technological movement on the surface) is less than 6 hours. That is, by pouring in the evening on the floors in an apartment or office, you can already walk on them in the morning, put the tiles or rearrange furniture. In order to fill such a floor screed, it is necessary to use finishing mixes which allow you to work with a thinner layer of floor screed and ensure rapid hardening due to the higher cement grade and smaller fraction of sand. In addition, such leveling screeds are much easier to lay, which is due to the higher flowability of the mortar, and that, accordingly, accelerates the pace of work.

Calculating the amount of material required

Before buying dry mixture, it is very important to calculate the required amount of it. To do this, the first thing is to determine the height of the middle layer of the screed. This is done using the formula: (Hmax + 2Hmin)/2, where Hmax – the maximum height difference in the floor of the room, Hmin – the minimum thickness of the screed layer. For the above example, where the maximum difference was 30 mm, and using a dry mixture which allows working with a minimum layer of 10 mm, we obtain an average layer height equal to (30 mm + 2 * 10 mm)/2 = 25 mm. Further multiply the number obtained by the total area of the room where you intend to do screed, and the expense material (it is different for each individual mixture, but on average is 2kg/mm/m2). Thus, in order to make the ideal screed throughout the apartment area of 40 m2, we will need about 40 * 2 * 25 = 2,000 kg, ie up to 80 bags. However, in practice, often such a huge layer is not required and ideal differences do not happen, so the average layer will be about 12-15 mm.

For good adhesion to the floor must first be completely cleaned of dust, such a surface must be dry and solid. In this regard, manufacturers highly recommended to use a primer, which not only completely eliminates dust, but also further increases the adhesion. And already when buying the dry mixture, it is important to think about the additional purchase of a primer, if it has not been bought earlier for other works.

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