Floor screed mortar: types and proportions

Selecting the appropriate floor screed mortar is crucial for any building endeavor. The appropriate combination can significantly impact durability and finish, regardless of whether you’re building a new structure or remodeling an old one.

Floor screed mortar comes in a variety of forms, each with a specific function. Which one to select will depend on the particular requirements of your project, including load-bearing capacity and the kind of flooring that will be put on top.

Achieving the proper proportions is also crucial. The strength and durability of the screed can be affected by the proportions of cement, sand, and other ingredients. A smooth, level surface that is prepared for any final floor covering is guaranteed by a well-mixed mortar.

The various varieties of floor screed mortar and the suggested ratios for each will be discussed in this article. Whether you’re an expert builder or a do-it-yourself enthusiast, this guide will assist you in finding the ideal combination for your flooring project.

Types of screeds

• Cement-sand. Used to level the surface under the finishing coating: parquet, linoleum, board, ceramic tile, porcelain stoneware and other types of finishing floors. When strengthening the surface with ironing and subsequent painting, it can be used as a finishing coating, relevant for technical rooms and rooms with high humidity.
• Self-leveling screed. For the construction of this structure, ready-made packaged material produced industrially is used. The screed can be used as a base for the finishing floor and as a finishing coating.
• Dry screed. Also equipped with special hard materials. This type of screed is able to level out small unevenness. It is made using a special technology, so it is best to order such a screed from experienced specialists.

We will focus more on the cement-sand option for laying the floor base because, in spite of new construction technologies, it is the most popular and doable for self-construction. We will discuss the thickness of the screed, the amount of cement needed for the floor screed, how to calculate the number of components, how to iron floors with cement, and other relevant practical issues.

Thickness of the cement-sand screed

The amount of building material used, as well as the final product’s strength and durability, are all influenced by the structure’s thickness. Regulations stipulate that a product must be at least 40 mm thick. Other values for the screed’s thickness are advised by construction practice based on the particular construction option:

• Not less than 50 mm when installing on a reinforced concrete base (slabs). Technical meaning – preventing rapid removal of moisture into the thickness of the slab and corresponding preservation of the strength of the screed.
• Not less than 70 mm when pouring onto a waterproofing layer, without reinforcement on wooden floors or ceilings resting on deformable beams.
• Not less than 100 mm when using expanded clay clay or sawdust as a filler (warm screed).

You can thin the screed to a thickness of 30-35 mm by using plasticizers based on polymers. However, because these additives are expensive, their use is only financially viable when preserving every millimeter of floor rise is the goal. Crucial! Utility lines should have a minimum thickness of 25 to 30 mm if they are situated in the screed thickness over pipes, heating wires, or cable channels.

A level and sturdy foundation for any flooring requires a well-made floor screed mortar. To get the best results, it can be helpful to understand the different types of mortars and the proper ratios of materials like cement, sand, and water. In order to guarantee a smooth and durable finish, this article examines the various types of floor screed mortars, their ideal mixtures, and helpful application and mixing tips.

Proportions of cement and sand for floor screed

The typical ingredients of a floor screed solution are Portland cement, clean water, and sifted washed sand. The following ratios are used to prepare the material that will fill the structure: One part water, three parts sand, and one part cement.

Here, the water amounts are referenced and empirically determined. Add 0.5–0.6 parts of the cement immediately, mix, and then add small amounts while mixing until the desired consistency (thick sour cream) is reached.

What brand of cement is required for floor screed is a crucial detail. The above solution proportions are provided for the most economical and best-performing cement brand, CEM I 32.5N PC (previously known as M400).

Cement mortar for floors. Calculation

The accepted thickness of the structure and the dimensions of a given room determine the required consumption of the solution and the corresponding number of components. As a result, for instance, you ought to set the following values: 50 mm thick screed, 3 x 5 meters of space.

• We bring the thickness of the screed in millimeters to the thickness of the screed in meters: 50/1000 = 0.05 m.
• Determine the area of ​​​​the room: 3×5 = 15 m2.
• We determine the volume of the solution for pouring the screed: 15×0.05=0.75 m3.
• We determine the cement consumption for a floor with an area of ​​15 m2. As already mentioned, the ratio of cement-sand components is 1:3 or 4 parts. To determine the amount of cement in m3, we divide 0.75 m3 by 4 parts=0.1875 m3 of cement is needed to prepare a floor screed for a room of 15 m2. Sand will be required 0.01875×3=0.5625 m3.

The majority of developers won’t care about the cement volume in m3. We change one m3 to a kilogram. For practical calculations, the generally accepted specific density of Portland cement is 1,300 kg/m3. Consequently, the amount of cement needed for our screed is 1300×0.1875= 243 kg.

You can quickly and precisely determine the necessary amount of binder and sand by entering your values for the layer thickness and room dimensions into the provided formulas.

Solution for underfloor heating screed

As mentioned previously, the floor screed can serve as insulation in addition to its intended use for surface leveling. In this instance, the solution’s composition for building the structure will differ. Materials that are "warm" are added to the solution in this instance.

Adding sawdust and lime to the cement-sand mortar is the least expensive, yet most efficient, solution. Three different kinds of recipes exist for how to deal with a warm screed:

• High density, kg: 1 part cement, 1 part sawdust, 1.5 parts sand, 0.25 parts lime.
• Medium density, kg: 1 part cement, 1.3 parts sawdust, 2.3 parts sand, 0.6 parts lime.
• Low density, kg: 1 part binder, 4 parts sawdust, 1 part sand, 2 parts lime.

How much cement is needed to fill a warm screed floor? In this instance, you should calculate the amount of the remaining components using the specified proportions and set the cement amount in kilograms.

How to iron a concrete floor with cement?

"Iron" must be used to reinforce the cement screed’s exterior, which will serve as the finishing floor. Ironing not only hardens but also virtually eliminates dust and greatly extends the life of the structure. The hardening technology must be used with the following supplies and equipment:

• Dry Cement CEM I 32.5N PC.
• Turnomer or spatula.
• The spray of water.

Partially from the far wall of the rooms toward the doors, the screed—which will be ironed—is poured. The length of the person’s arm should completely cover the area of the next portion at the same time.

The surface of the subsequent screed section is immediately covered with a continuous layer of dry cement, 3–4 mm thick, following pouring and alignment. Water is sprayed onto the cement until it is fully moistened.

Crucial! It’s important to handle wet cement carefully to avoid blur! The moistened cement "rubs" into the screed with light circular trowel or spatula movements until a smooth, wet, blue-green surface appears.

Conclusion

In conclusion, it is important to note that retailers and producers of dry construction mixes sell a ready-made, customized cement-sand screed that comes in different-sized paper bags and is dosed with components.

Purchasing a pre-made screed is incredibly convenient as it eliminates the need to calculate and weigh individual components. But this "convenience" comes at a price: the cost of materials will go up by at least 100%. Determine for yourself whether it makes more sense to use this article to calculate and purchase the necessary amount of materials or to pay twice as much for a pre-made screed.

A smooth and long-lasting floor surface is achieved by selecting the appropriate floor screed mortar. Knowing the various mortar kinds and how much of each will help you make sure your floor screed is suitable for your needs.

There are numerous varieties of mortar that are appropriate for distinct uses. The secret to success is knowing the proper mix ratios, whether you’re looking for a basic cement-sand mix for a straightforward project or a more complex self-leveling compound for a high-traffic area.

A key factor in the screed’s strength and longevity is proportion mixing. Achieving the best results requires adhering to recommended guidelines regarding the ratios of cement, sand, and water. Recall that for a perfect finish, consistency in mixing and application is necessary.

In conclusion, a properly prepared floor screed mortar prolongs the life of your floor while also improving its appearance. Any flooring project can have a strong foundation if the right type is chosen and mixed properly.

Video on the topic

Composition of an ideal screed for a warm floor

Solution for screed. Semi-dry screed.