How To Install A Semi-dry Screed On Expanded Clay Backfill

2023 Author: Philip Bishop | [email protected]. Last modified: 2023-08-25 07:54

• Pros and cons of expanded clay
• Types of backfill
• Terms of use
• Screed layers
• Necessary materials
• Preparatory activities
• Semi-dry screed
• Expanded clay with solution
• Professional advice

The floor screed can be done using various materials. It all depends on the purpose, as well as the desired result. Under certain circumstances, a semi-dry floor screed can be arranged under a "warm floor" or under any floor covering. Cases of installation of a "rough" floor on expanded clay, which is famous for its main advantages, are not uncommon. In addition, it is important to observe the technology itself so that negative consequences do not appear.

Pros and cons of expanded clay

The use of expanded clay in a semi-dry screed provides the following main positive qualities:

• This floor is not afraid of severe frosts, as well as high temperatures. No heat will damage the subfloor base. A semi-dry screed with expanded clay can be performed even in those rooms that are not heated throughout the year.
• With the use of expanded clay, any irregularities are eliminated, no matter how high they are. It is possible to install a floor screed to a height of 150 mm. Some mixtures in this case may be powerless.
• Using expanded clay concrete, you can be sure that rotting does not appear, it resists high temperatures, as well as the formation of corrosion. The service life is very long.

• The basis of expanded clay is burnt clay. Its weight is much less than that of conventional concrete. The overlap pressure and load is reduced to a minimum. It can even be used on a wooden base.

  

Among the shortcomings, the instability of this material to moisture is especially disturbing. For this reason, there are some restrictions on its use in certain circumstances.

Expanded clay should be stored under a special canopy or even indoors. The fact is that this material absorbs moisture very well, but at the same time it slowly releases it. In this case, after the repair, the room will remain at high humidity for a long time.

Types of backfill

The density of expanded clay is different. The range of products is presented on the construction market. It remains only to choose a more suitable option for the device of a semi-dry screed indoors. The density can range from 250 to 600 kg per cubic meter, which meets the specific circumstances of use. Depending on this, types are distinguished:

1. Crushed stone. The size of each granule is 10-14 mm. Its main field of application is concrete preparation.
2. Expanded clay sand for dry screed. It is necessary when it is required to create a thin screed, The size of expanded clay does not exceed 5 mm.

3. Gravel. It allows you to get a very light, but at the same time quite durable floor. There are also three categories of expanded clay granule dimension: 20-40 mm, 10-20 mm, 5-10 mm.

   

When choosing a specific backfill, one should proceed from what technology of the subfloor device will be used, as well as the room itself where the installation work is carried out.

Terms of use

Semi-dry floor screed with expanded clay can be performed only under certain conditions. The most basic is the device of a thick screed, the thickness of which ranges from 6-10 cm. To begin with, a layer of expanded clay is poured to level the surface, and only then a cement-sand screed is poured.

Also, expanded clay is used so as not to create loads on the floor, especially if it is an old building.

The cost of such a material is not high and it will noticeably reduce all costs by removing a sufficient amount of cement in the solution.

Expanded clay shows a huge number of qualities, and the most basic of them is an excellent layer of heat and sound insulation. Due to this, it enjoys sufficient popularity among buyers, newcomers to the construction business and professionals.

Screed layers

Before you start work, you should find out what layers a semi-dry screed for a warm floor includes. First of all, it is a protective layer of waterproofing, which must be combined with a damper tape. One should not be afraid to make a larger layer in height, since in the future it will all be cut off after the end of the installation work. After that, expanded clay is filled up with the required height, along which the beacons are set. Beacon options can be different. Everything will depend on imagination and possibilities.

When all of the above is done, a semi-dry screed is poured, serving as a subfloor. If necessary, a reinforcing mesh is added to it, which can be replaced with fiberglass, which has been popular recently due to its large number of positive qualities.

Necessary materials

Of course, a tool is prepared for performing floor screed indoors. It is very important to buy all the necessary material for work. You can even calculate in advance what and in what quantity is required.

If the room is 5 * 3 meters in size, that is, 15 m ², then the optimal screed layer will be 50 mm. From this it turns out that the total screed we need is 0.75 m ³ (area multiplied by the thickness). In this case, the proportions of usually sand and cement are 1 to 4 (sand 0.6 m ³, and cement - 0.15 m ³).

Sand will be needed for filling under expanded clay. If we take an approximate height of 20 mm, then 0.3 m will come out. ³. Roughly speaking, such a room will require almost one ton of sand. Depending on the density of expanded clay, its amount is also calculated. With average indicators and a thickness of 100 mm, it will take 1.5 m ³. This option is suitable for making a "wet" screed. But the device of a semi-dry screed is not much different, where it is necessary to buy the appropriate mixture with additives.

As for the lighthouses, their number, first of all, will depend on the rule used, its length. With its length of one and a half meters, the above room will require about five lighthouses throughout the entire area. The length of such beacons is chosen over the entire width of the room - three meters.

The choice of the expanded clay itself is focused on granules, or rather their fraction. To calculate everything correctly and independently, it is enough to open the calculation calculator, which can be found on the Internet. In this case, it will not be superfluous to seek help from familiar builders. They will tell you the exact amount of material to purchase. It should be noted that the materials for underfloor heating screed are no different in quantity.

Preparatory activities

The same preparation is carried out both for normal screed and for semi-dry. That is, it makes no difference whether the floor screed is dry or semi-dry will be needed for the flooring. It is very important here to level the foundations where the work will be carried out. All existing cracks and pits, if possible, are eliminated with a cement mortar. Bumps can be knocked down. We must not forget about the waterproofing layer, which can be a regular plastic film. The better the material is chosen, the better qualities it can display during operation.

After that, sand is poured, acting as a pillow under expanded clay. Usually its layer is 20-30 mm. The pillow should also be leveled and leveled using a rule of thumb. As for tamping the sand, it will be enough just to walk along the entire plane. In this case, the weight of a person will be enough.

The choice of expanded clay is carried out depending on the fraction (fine, medium and large fraction). He falls asleep throughout the room, starting from the far corner. After filling the required layer, it should be leveled. On top of expanded clay, beacons are installed, which serve as the main one for the sub-floor level.

Profiles are used as lighthouses, which are mounted on the base using a cement-sand mortar. Subsequently, the screed is poured, somewhat stepping on the beacons, and they simply "hide" into the base of the subfloor.

Semi-dry screed

When expanded clay is filled up, you can choose two options for further actions:

1. Pouring cement milk. Installation of the solution is carried out directly on expanded clay. The granules absorb moisture very easily. If this happens after pouring a semi-dry screed, then drying may occur unevenly, which will lead to shrinkage over the area. Some pre-wet the granules in water, and only then backfill. But even this option does not give one hundred percent guarantee.

   

2. Separation of expanded clay from a semi-dry screed with a layer of waterproofing. Moisture from the solution will not get into the bedding, even if you just lay a plastic wrap. The main thing is that it is intact over the entire surface and is not torn during the installation of a semi-dry screed.

Not everyone knows how to make cement jelly. For this, water is used twice as much as with the standard version of the screed. Depending on the result obtained, it should be considered whether it is necessary to add additional water or cement. In this form, after pouring expanded clay, it is necessary to let the layer brew and dry up for at least a day. Only then can a semi-dry concrete floor screed be poured.

If the beacons are removable, then they are pulled out only after a few days. The resulting grooves are sealed with mortar, carefully tamped and sanded until a uniform layer is obtained.

Expanded clay with solution

There is also such an option for performing a semi-dry screed, when the solution itself is mixed with expanded clay granules. This process takes much less time than in the previous case.

Expanded clay is poured into the container, which is prepared in advance, which is filled with water in the required amount. Mixing is carried out using a mixer. A ready-made dry mixture is poured into this, which must be thoroughly mixed until a homogeneous mass is obtained. You should be very careful with the amount of water. After all, a semi-dry screed requires a small amount. Overkill will lead to the manifestation of negative qualities.

There should be no lumps when stirring, and the granules themselves should become wet and acquire a gray tint. The mixture becomes slightly thick, resembling sour cream in consistency.

The prepared base is poured with a ready-made solution to a thickness of 20-25 mm. But the thickness will depend on the evenness of the floor, as well as on the final result that is required for the flooring. The reduction in time occurs for the reason that there is no need to wait a day for the first layer, filled with cement milk, to dry and harden.

After the initial layer of the "pie", a second and subsequent one is carried out until the formation of a "rough" floor. During the work we do not wait for the previous layers to dry. The finishing layer is not only carefully rammed, but also leveled.

Professional advice

Semi-dry floor screed requires certain knowledge and experience in performing work. Even small nuances will avoid possible problems in the future during operation. Some of them:

• When placing the wires on the floor, under the future screed, they should at least be wrapped in polyethylene, and also attached to the base of the floor with adhesive tape.
• To avoid cracks in the poured concrete mortar, it is best to add a plasticizer to it. It will be enough only for the finishing layer of a semi-dry screed.
• Not only polyethylene film, but also bitumen mastic, waterproofing, etc. can serve as a waterproofing floor.
• After pouring the screed, you should take care of the surface. The main activity is periodic wetting using a spray bottle.
• The drying time of the screed is about a month. The longer it stands without external pressure, the more strength it can gain in the end. Much will also depend on the flooring used.
• Beacons can be metal rails or special profiles, called "beacon".

Compliance with the screed technology, whatever it is, will allow you to get a flat surface of the subfloor, on which you can immediately carry out the flooring.

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