Semi-dry screed for heated floors and outdoors: pros and cons, differences from dry

Semi-dry screed is called screed, to which a minimum of water is added. Compared to wet, this is not a solution, but an elastic mixture that hardens in a matter of hours. Therefore, installation work is easier to carry out, and the surface is quite smooth. The pros and cons of semi-dry screed, the technology for its implementation and differences from other finishing methods are described in detail in this article.

Composition and properties of semi-dry screed

Semi-dry screed outdoors and indoors is a mixture of cement and sand with additives that improve its properties and increase its service life. The mixture must be prepared with water, this is the similarity between a semi-dry screed and a wet one.

However, unlike the latter, the semi-dry method involves the use of liquid in very small quantities. That is, it is taken in such a volume that the mass becomes plastic, but no more. As a result, the composition does not flow, but simply rolls into lumps that hold their shape well.

A semi-dry screed is used for heated floors, indoors and outdoors. If you compare all types of technology, you can find several differences.

A floor made using this technology looks like this.

Advantages and disadvantages

If we consider the advantages of the semi-dry method, several points can be highlighted:

1. A perfectly flat surface with no differences or even small cracks. The high strength of semi-dry screed is ensured by the minimum amount of water required when preparing the mixture. This technology compares favorably with the wet method.
2. High laying speed thanks to the use of special equipment, with which the solution can be applied even to great heights (up to 100 m). However, there are also disadvantages of semi-dry screed - it is not easy to cope with the work yourself, without professional installations.
3. The composition dries very quickly, because a minimum of water is used for mixing - it is only enough to obtain a plastic consistency. A semi-dry floor screed, the photo of which is shown below, is completely ready after 4 days, unlike a wet one, which takes up to 3-4 weeks to dry. You also need to keep in mind that walking on a floor made using semi-dry technology is allowed after 12 hours.
4. There are no leaks because the water is completely absorbed into the cement. This is the advantage of semi-dry floor screed and the disadvantages of the wet method, when there is a risk of leakage. However, in both cases a layer of heat or sound insulation is provided.
5. The difference between dry and semi-dry floor screed is obvious - in the first case, water is not required at all, and in the second it is needed, but in small quantities. Moreover, despite the presence of liquid, the composition dries very quickly. Therefore, you can continuously install coatings of different heights in the same apartment. Thus, if necessary, you can create a multi-level floor and use a variety of types of finishing coating.
6. Finally, an important factor is the low price. For example, in the case of the dry method, the cost can be 2 times higher than the semi-dry technology. And the classic wet method costs a little more. But if, for example, a semi-dry screed is made on a warm water floor, this increases the cost of the technology, as in other cases.

To make the coating smooth and durable, reinforcement is carried out with a semi-dry floor screed. This also increases the overall cost, but also increases the service life. However, despite the obvious advantages, this technology also has its disadvantages:

1. Certain conditions are required for installation. It is necessary that there is a positive temperature outside or indoors without the risk of frost (even small ones up to -2 degrees). Otherwise, the sand freezes, and a semi-dry screed under a warm water floor will not work: it will be impossible to both supply the solution through a pipe and work with it.
2. The work is not difficult, but special equipment is required, for example, a construction mixer. If you plan to lay the floor outdoors or on low floors, you can transport the mixture yourself. But if the volumes are large, it is easier to feed vertically through a pipe, which again requires professional tools.

Both problems are completely solvable, especially if we are talking about a small room, for example, an apartment. First of all, it is important to choose the right composition - what matters is the strength grade of the semi-dry screed, its composition and the brand of the manufacturer.

It is better to plan the work during the warm season. But even if this is impossible, you can organize special heating of the composition, insulate the hoses and introduce an anti-freeze additive into the batch.As for the problems with the delivery and process of preparing the mixture, they are relevant only in cases where it is planned to work over large areas.

Step-by-step installation instructions

A floating semi-dry screed is laid using conventional tools:

• shovel;
• rule;
• Master OK;
• grater;
• building level;
• rammer or vibrating plate.

In this case, the materials you will need:

• sand;
• cement (grade for semi-dry screed minimum M400);
• fiber reinforcement;
• additives (plasticizers);
• damper tape;
• profiles that are used as beacons.

Step-by-step installation instructions are as follows:

1. First, prepare the old base, remove the previous coating and seal the cracks. You will also need to level the protrusions, level them and completely clean them of dust.
2. The semi-dry screed technology for heated floors involves preparing a cement mortar and applying it along the joints of the floor and walls. After this, the composition is distributed over the rest of the surface. When the primer has dried, cover the floor with a thick film, overlapping the fragments by at least 10 cm and gluing them together with tape. The edges of the walls (along the connection with the floor) are covered with damper tape.
3. At the next stage, installation of a semi-dry screed comes down to installing beacons from the profile to determine the surface level. They are mounted using a laser level. Self-tapping screws are attached to the base and reinforced with a solution of the mixture that will be used to lay the screed (it is prepared in the next step).
4. Now you need to mix the mixture in a manual or electric concrete mixer. Water is added in small portions to create a dense, elastic mixture that is easy to form into a lump.Moreover, when compressed, it should not crumble, much less release water. When the composition is ready, add reinforcing fiber strictly according to the instructions.
5. As you know, floor screed has pros and cons. For everything to go right, it is important to lay out the bottom layer and then compact it using a tamper. Only after this the top layer is applied and leveled using the rule. The work is carried out quite quickly, since the solution hardens in just an hour.
6. When the surface dries, you can remove the beacons and rub the resulting depressions with the remaining mixture. If you are screeding a semi-dry floor in winter, this should be done as quickly as possible. Another point - if the area of ​​the room exceeds 15 m2, you need to cut 3 mm seams in the surface of the screed using a spatula. They will provide strength in case of narrowing and expansion of the web due to the effects of low and high temperatures, respectively.

Semi-dry screed is a more advanced technology compared to wet and even dry. In essence, this is a kind of “middle” option that combines the advantages of two other technologies. If you process a small area, the use of special equipment (with the exception of a concrete mixer) is not necessary.