In the process of laying or repairing the floor, the screed is the main point, since the top floor covering is laid on a perfectly flat plane. For a quality screed, you need to calculate everything correctly:
- Select the desired thickness.
- A kind of screed.
- The composition of the solution.
The maximum and minimum thickness of the floor screed should be determined first and foremost: the stability and durability of the coating directly depend on these characteristics. A very thin layer will not be able to provide the reliability that you are aiming for, and with a thick layer, a large load on the overlap is very likely.
Conditions affecting screed thickness
The minimum thickness of the floor screed is formed in each case personally, depending on:
- How is the styling done?
- What materials are used for screed.
- Under what coating (linoleum, laminate, etc.) is the base prepared.
Because the screed can be formed both on a heat and sound insulating layer made of solid or bulk materials, and on a concrete coating.
The thickness of the screed also depends on the evenness of the base, respectively, the worse it is, the thicker the composition layer should be, since almost all coatings need a completely flat surface.
Diagnosing floor roughness
In order to calculate the thickness of the screed floor, it is very important to take into account the specifics of your base: the difference in height and the presence of recesses. It is not enough just to look and understand whether the floor is flat or not. If, when considered, it seems even, then when checking with a building level or bar everything can change. It is necessary to walk the device on the floor, and you can notice the existence of holes between the building level and the base. If slight gaps were found, then the floor will need to be leveled with a screed.
Basically, the thickness of the screed in the living room, where the old coating is replaced with a new one, ranges from 3 to 5 cm. Some mistakenly believe that the thicker the base, the better. However, this is not so at all, do not forget that the purpose of the screed is to level, and not to increase the height of the floor covering.
In addition, if the screed is carried out as usual filling the surface with a thick layer, the surface will not become smooth, and will dry out for a very long time, thereby creating great inconvenience.
Minimum thickness
When calculating the thickness of the screed, several factors should be taken into account:
- On what basis is it formed?
- What mixture is used for it.
When pouring the composition onto concrete slabs, the minimum thickness of the floor screed should be 20 mm.
When laying the solution on heat or sound insulation from loose or solid materials, the layer should not be less than 40 mm, and hardening with a metal mesh is also required. The same rules must be followed when pouring the solution onto the waterproofing layer in the bathroom and in the kitchen.
In accordance with SNIP, the thickness of the screed for blocking pipelines should differ from the diameter of the pipes by 10-15 mm in a larger direction.
Of course, the thinner the screed layer, the more economical the repair will be, but do not forget that “the avaricious pays twice”, so some factors should be taken into account:
- A thin layer forms a rapid evaporation of moisture, which can provoke cracks in the screed.
- A thin layer of screed may not “adhere” to the base;
- Possible violation of the integrity of the screed when things fall.
Maximum thickness
The maximum thickness of the screed is determined for each case separately. Basically, this indicator is indicated on the box or in the memo to the solution. The maximum height for all solutions is different, it ranges from 20 to 80 mm. Experts recommend using a “coarse screed” to smooth out impressive level differences, since it copes with the task and is much more profitable than a dry screed.
If we talk about the maximum thickness, then there are principles of what thickness is used for different coatings:
- When laying on a flat concrete surface, 20 mm is enough.
- When laying on thermal insulation - 45-50 mm.
- On a cold pipeline - 10 mm.
- On hot - 20 mm.
When laying out a large volume, it is required to leave a cushioning layer of 20 mm at the edges, which is required to expand the material during heating. This layer can be repaired using construction foam or special tape.
The maximum thickness for a dry mix does not exceed 80 mm. This is explained by the fact that this material practically does not evaporate moisture.
The usual composition of cement and sand is allowed to be laid with any layer, however, professionals do not recommend making it higher than 150 mm, the exception is pouring onto the ground.
Classification
In total, three types of screed are distinguished by thickness:
- Thin draft. When choosing this type, self-leveling solutions are used, allowing to form a thickness of up to 20 mm.
- Screed up to 70 mm high. To create it, reinforcement from iron mesh or reinforcement rods is used.
- Maximum thickness up to 150 mm. It is formed by laying out a monolith with an internal iron frame.
Mixture composition
The minimum thickness of the screed as well as the maximum, directly depends on the composition of the mixture and problems with the base.
If thresholds of less than 20 mm and minor irregularities are detected, it is recommended to use self-leveling compounds, which ultimately give an even and thin layer. They independently, without the help of a person, spread over the surface. After the solution dries up, you can immediately begin to lay out the top coating. The composition of the solution includes:
- Cement or gypsum.
- Fine sand.
- Plasticizers to improve quality.
- Paste.
- Pigments.
With minor defects, the minimum and maximum thickness of the floor screed in the apartment is set by the manufacturer of the composition.
In addition to the above, there are some more recommendations on the height of the screed:
- If the screed is formed on top of the insulating layer, it is required to leave about 40 mm between the wall and it. Subsequently, it will be filled with insulating filler. Professionals recommend monolithic screeds to be fenced off from the walls with a waterproofing film.
- For laying on plates, the thickness should be 10 mm.
Cement and sand screed
This compound is used to compensate for bumps above 20 mm. Since the sand-cement mixture contains plasticizers, experts say that the thickness of the cement screed for the floor should be at least 30 mm. With a smaller thickness, cracks will necessarily appear over time.
Coupler at high differences
There are cases when monolithic plates are laid very poorly, as a result of which strong level differences are formed by more than 60 mm. In this case, it is recommended to screed from a solution of a mixture of concrete and coarse sand. The thickness of the concrete screed for the floor can reach up to 100-150 mm. In the most neglected cases, when the slope and thresholds reach huge values of 150–170 mm, it is necessary to make the lower layer of screed made of expanded clay concrete, otherwise the cost and weight of the screed will be just very high.
Dry floor
In the presence of significant defects, a dry floor screed is often used to accelerate the process, which includes substances that do not require long drying. The screed includes a layer of raw material, for example, expanded clay, and sheet material (plywood, chipboard, etc.) is covered over it. If necessary, it is possible to carry out hydro, heat or sound insulation. The thickness of such a coating is from 35 to 60 mm.
Water floor heating
When the question arises of how thick the screed should be, then here you should first clarify some points. The fact is that in the device of a warm water floor, the screed performs two functions simultaneously. First of all, this, of course, is the basis for the final coating, the second is the accumulation and distribution of heat. In addition, the layer also performs a protective function, namely:
- Protects pipes from damage.
- The top layer of the floor from overheating.
- Sound and heat insulation are formed on the lower layers.
Therefore, to understand what thickness of a coupler for a heat-insulated floor should be, is required for everyone who is engaged in repair.
Especially for the implementation of underfloor heating, inertial solutions are manufactured that are able to conduct and retain heat for a long time. The remaining solutions are not suitable for this, since they “eat” heat. In addition, temperature differences occur quite often in the underfloor heating device, which adversely affects cement and sand screeds.
The best solution for a warm floor at the moment is a bulk floor, for the reason that it is very plastic and dries quickly.
So, what thickness should the floor screed be in the device for a warm coating? In this case, a high screed will “eat” heat, and it will not be easy to adjust the temperature regime. But on the other hand, the coating will warm up for a long time, which means it will hold more heat.
Too thin screed is also not a good option. In this case, overheating can occur, and heat will be distributed in places where the pipes are laid.
In the apartment, the screed should not be thicker than 100 mm and thinner than 70 mm, a layer of mortar above the pipes - 20-50 mm. In some cases, the design turns out to be slightly "hanging": in the middle of the base and flooring, thermal and noise insulation is carried out, in this case it is better to create a layer of at least 35 mm.
Another important parameter that determines the thickness of the screed for a warm water floor is the material of the heating element. A solution of 30 mm thickness must be placed above the water floor pipes.
What can lead to improper installation of the screed?
If the installation technology is not followed, the performance properties of the screed are reduced. It is very important to observe the slope of the coating level, in case the coefficient is exceeded by 0.2%, the finish coating will not fall according to the rules.
In the base, evened out poorly, gaps may form between the topcoat webs. And about such reviews, when unskilled repairmen simply sprinkle cement on the floor and pour it on top of the water, I don’t even want to talk. Messages about such cases can be easily found on specialized forums. A screed laid with irregularities quickly begins to crumble, and will never become a reliable foundation for any topcoat.
Such alignment must be broken by a punch, removed from the apartment and reassembled. The work of unprofessional craftsmen guarantees extra costs and loss of time. It is much better to do the work on your own in compliance with all the details and moments, but most importantly, adhere to the recommended thickness of the screed.
As you can see, it’s not difficult to calculate the parameters. However, depending on the type of screed, you need to consider all the nuances that you now know about.