The semi-dry screed device is similar to traditional pouring with concrete or a special mixture. It can be used when leveling the rough surface, and after grinding it can be used as a finishing floor in non-residential premises. Since the composition of the mixture in the case of a semi-dry screed differs from the traditional one, the technology of the pour itself also changes. The essence of the method is quite well reflected in the name: the solution is mixed with a much smaller amount of water. Although the volume of the latter is taken as minimal, it should be sufficient to hydrate the cement in the mixture. In appearance, it most likely resembles wet sand, and not ordinary cement mortar.
Pros of a semi-dry screed
A mixture that is free of excess water, hardens, resulting in not only less weight, but also simplifies the process of laying and leveling. However, these are not all the advantages of a semi-dry screed:
- The density, and therefore the strength of such a mixture is higher than the traditional one. The absence of excess water reduces the number of voids formed. It is toopositively affects the strength of the monolith.
- Such a mixture is almost not subject to shrinkage, which eliminates errors with its final thickness.
- Less water in the mixture makes it harden faster.
- Semi-dry screed technology is cleaner than traditional. In addition, the risk of flooding neighbors is reduced.
- The use of such a screed does not significantly affect the level of humidity in the room, and therefore does not adversely affect the quality of other finishing works.
You can walk freely on such a screed after twelve hours after laying. Other finishing works in the room, excluding the application of finishing materials, begin in just a day. Less time elapses before laying the final coating on the floor.
Disadvantages of semi-dry screed
But, like any method, a semi-dry screed has its drawbacks:
- A thick mixture does not spread well, making it very difficult to achieve clear corners, instead of which smooth transitions are formed.
- Labor intensity of manual laying of semi-dry screed over large areas.
- The minimum thickness of such a layer is three centimeters, and the optimal value is from four to five centimeters.
These shortcomings are not fatal and can be compensated for. The negative effects of the high density of the mixture can be combated by adding plasticizers to it. Right angles between walls and floor are obtained by ramming.
Required screed thickness
Due to the lack of excess in the mixturewater, the hardening rate of such a screed is very high. If the thickness of the laying is less than necessary, it may dry faster than it sets to the subfloor. As a result, the solidified solution will flake off and quickly collapse under the influence of loads. A screed with a thickness of more than five centimeters will be very heavy, each extra centimeter adds up to 120 kilograms of weight per square meter. Therefore, if you need to raise the level of the floor, it is better to lay expanded clay or expanded clay concrete in the first layer, and only apply mortar on it.
In the process of work, it is better to use a floating floor scheme, in which the mixture does not directly contact either the base or the walls. Such a screed is separated from the draft surface by a layer of waterproofing, and from the walls - by a polystyrene foam tape, which provides additional soundproofing. Another advantage of such a composition will be that stresses arising in the structure of the house are not transferred to it.
Semi-dry screed reinforcement
Reinforcement is used to strengthen the semi-dry screed. Fiberglass is becoming increasingly popular, which is gradually replacing the usual construction mesh. This material has the following advantages:
- fiber fiber is added to the screed at the stage of preparing the mixture, which significantly reduces labor costs;
- reinforcing threads are evenly distributed throughout the volume of the solution, and strengthen the screed in all directions;
- fiber prevents cracking while mesh onlyprevents their increase.
The use of traditional rebar is less efficient. If, nevertheless, for some reason it is necessary to use a grid, then this is done as follows:
- The first layer is applied up to three centimeters thick.
- A leveling layer up to two centimeters thick is poured on top.
Surface preparation
To ensure the durability of the floor, you must first prepare the base. First, surface defects are eliminated. The recesses are filled with cement mortar, and the protrusions are removed with a perforator. Then the floor is cleaned of debris, checked by level, and the height difference is determined with a level. The surface is lined with a special material or durable polyethylene. It is overlapped, and the joints are fixed with construction tape.
A damper tape no thinner than four millimeters is glued along the perimeter of the walls. Such a strip provides free movement of the entire structure, but also works as a soundproofing material. To facilitate the alignment of the screed, beacons can be installed. A T-shaped metal profile is well suited for the installation of guides. Beacons should be placed at regular intervals and fixed with cement mortar. When installing them, you need to focus on the longest wall, with a step slightly smaller than the rule indicates - it will be easier to level the mixture.
Requirements for the components of the solution
When calculating the amount of materials required for a semi-dry floor screed, first determine the allowable volume of the mixture, based on the area of \u200b\u200bthe room and the thickness of the intended layer. After that, you can proceed to the purchase of the main components:
- cement - better to choose brand 400 or 500;
- high quality sand (quarry or river);
- plasticizers to increase the fluidity of the mixture.
When making a mixture, you can use some services and make it easier for yourself to work with a semi-dry screed. In the reviews, people note that in order to save time and effort when preparing the mortar, it is worth renting a concrete mixer.
Some special requirements apply to the ingredients of the solution. Sand should contain no more than 3% clay impurities, and various foreign inclusions should be completely absent. Humidity can be any, but it must be taken into account when calculating the amount of water added to the mixture.
When buying cement, you should always pay attention to its expiration date and the integrity of the package. Naturally, you should not save money by buying low-grade cement. Not any water is suitable for preparing a solution. It is best to use tap water. Water from natural reservoirs must be tested before use, as it may be contaminated.
Mix preparation
Dry mix is made at the rate of three parts of sand and one part of cement. Mix thoroughly until dry before adding water. Water is taken in such an amount that the consistency of the solution is similar to sandy loam (sand with clayeyimpurities). Such a mixture should easily stick together into a lump, without releasing excess moisture. When reinforcing the screed with fiberglass, it should be added to the water before introducing it into the mortar.
The natural moisture content of the sand affects the consistency of the mixture, so when adding liquid, overflows often occur. In this case, dry ingredients should be added to the solution, keeping their proportions.
Polypropylene fiber is added evenly to each bucket of water. This is necessary for its better distribution throughout the volume of the mixture. A little less than one hundred grams of fiber should be added to one bucket of water, but it is better to find out its exact amount from the manufacturer's marking on the package.
With machine cooking, you can make all the required volume of dry mix at once. When kneading the solution by hand, it is more correct to lay it out in layers. The first part of the mixture is rammed, after which the next one is laid out on it. The final layer is leveled with a rule and polished.
The mixture begins to dry out in less than an hour after adding water. The disadvantage of a semi-dry screed is that when using this technology, all materials must be prepared in advance, and work should be planned and completed as quickly as possible.
Pouring a semi-dry screed
A layer of waterproofing is laid on the subfloor. For these purposes, you can use thick polyethylene, roofing material or special material. Waterproofing strips are laid with an overlap, and the seams are fixed with construction tape. The material should go fifteen centimeters intowalls, forming a pallet.
A polypropylene tape with a width of ten centimeters and a thickness of eight to ten millimeters is laid along the perimeter of the walls. The required screed height is marked on the walls using a level (regular or laser). The first layer of mortar is laid below the level of the beacons, and then rammed. Then the second layer is immediately laid out, which is simultaneously rammed and leveled.
When the main work with a semi-dry floor screed is over, start grinding. In rooms with an area of fifteen or more square meters, expansion joints are cut along the walls to a third of the depth of the leveling layer, and no more than three millimeters wide. The laid screed is covered with a film and left to harden for a period of one day to one week, depending on the conditions. In hot and dry weather, the surface with the drying mortar must be moistened with water, otherwise it will dry too quickly, which can lead to cracking.
How long does a semi-dry screed dry
When the solution dries, the surface does not shrink and you can start grouting immediately after leveling the floor with the rule. Then you need to wait for the final drying. Reviews of a semi-dry screed indicate that it is possible to walk on such a floor after twelve hours, and in a day to continue other finishing work.
Laying floor coverings can also be done earlier than with classic grouting. Please note that this does not apply to all materials. In twodays after the screed, porcelain stoneware and tiles can be laid. Linoleum flooring is started in a week. And laminate or parquet can be laid only after a month, as is the case with a conventional screed.
Semi-dry screed: reviews
Opinions about this technology are quite controversial. Some consider this method quick and effective, but they advise not to walk on the floor for a week. People recommend paying attention to the quality of materials and the correct proportions in the manufacture of the solution. The quality of work depends on these indicators. It happens that they complain about unscrupulous manufacturers. And yet, there are more positive reviews about the semi-dry screed.
