The use of cement-sand screeds is one of the most popular ways of leveling the floor indoors. However, it is best to use it only on strong ceilings, capable of withstanding a large weight of the structure.
The screed of sand and cement is the most difficult method of leveling the floor. At a thickness of 1 centimeter the weight of its square meter reaches 20 kilograms. When using concrete with light fillers and special levelers, the weight of a square meter of screed can be reduced to 16 kilograms. It should be noted that the minimum height of the screed of sand and cement should be at least 3 centimeters, otherwise it will start to crack and crumble.
Advantages and disadvantages of screeds from sand and cement
The screed of sand and cement means the use of water to create it, which dictates the need for waterproofing the surface. The advantage of this method of floor leveling is high strength and long service life, minus a large weight of the structure.
Preparing the surface
- In order to start the formation of screed of sand and cement - the surface of the floor must first be primed. The use of the primer should increase the adhesion of the screed to the leveling surface. The fact is that when drying, the lower layers of the screed can move, and the lack of quality adhesion can ruin the work.
- Next, inspect the aligned surface. From it, you need to remove all protruding parts, for example the ends of the iron reinforcement used to form the plates.
- We tap the entire surface of the prepared floor with a hammer, remove the exfoliated areas, for this you can use a special grinding machine.
- Thoroughly clean the base to be prepared from dust - walk around with a broom and then with a vacuum cleaner.
- Soil and grout the mortar with large potholes and technological holes on the slab.
- Prime the surface with a solution used for processing materials with a large porosity. Apply two coats of the primer, the second after the first coat has dried completely.
- After complete drying of the primer layer, start laying a special damping tape along the walls of the room. It serves three purposes:
- To protect the screed array in areas adjacent to the room walls from damage caused by temperature deformation,
- For sealing the room in the joints of the plates. They may have cracks in which water is leaking, used to make screeds of cement and sand.
- To protect the screed from damage caused by the presence of horizontal stress when it dries.
Layout of the level of cement-sand screed
The required level for which you plan to raise the floor using cement and sand screed should be indicated by means of a laser level. When calculating the required lifting height, do not forget that the minimum height of this type of screed should be 3 centimeters. The laser level is set on the surface and then mark with a conventional pencil the position of the laser beam on the walls of the room. Using the laser level allows you to mark on all the walls, without even resorting to the use of a padded cord.
Step-by-step instruction for the formation of cement-sand screed
First of all, it is necessary to take into account that it is necessary to form a screed of cement and sand with a positive ambient temperature of at least 5 degrees.
Beacons are installed in the first stage. Their upper edge should be level with the marking of the planned level of the screed on the walls. For the manufacture of lighthouses, special rails or a conventional metal profile are used to create false ceilings. The distance between the beacons should be less than the rule used for leveling the screed, usually they are located at a distance of one and a half meters from each other.
As the bases fixing beams of lighthouses to the base a mixture of sand and cement is used in the ratio of 3 to 1, while it is expedient to use cement of the mark "400".As an alternative to such a mixture, it is possible to use a plaster mixture diluted for the consistency of "thick sour cream".
Initially, beacons are placed near the walls of the room, their level is verified on the marks on the walls. After fixing them, a strong thread is stretched between them, along which the intermediate racks of the lighthouses are subsequently positioned.
Check for deformation of the beacons, they should not sag. If such deficiencies are detected, fix the sagging places with additional supports - heaps of cement-sand mixture.
Waterproof the surface. For this, the meta joints of the slabs and the exit of the utility lines must be closed with a polyethylene film. It is possible to cover the entire surface of the film with tape, having secured the sections of the roll material with the help of an adhesive tape.
Wait for a firm fixation of the beacons on the surface. This mass of solution dries for at least one and a half hours.
Prepare mortar to form a cement-sand mixture. The ratio of sand and cement take 3 to 1, use cement grade "400".
Mix the screed mortar. This can be done both in a special container and simply on the floor. On the sheet metal pour sand, and then cement, move the ingredients and form a hill with a crater, similar to a volcano and in the notch on top of the pile fill the water. Gradually mix all the prepared mass, starting from the top. The prepared solution should last for about a quarter of an hour.
Extremely wet the entire floor area, intended for this batch of water. Lopata, move the prepared mortar into the space between the beacons.
The superimposed mass is aligned using the rule, moving excess solution to the side, where its quantity is less.
Sequentially fill with a solution of all strips of the screed, moving from one lighthouse rack to the other, starting from the more inaccessible part of the room and heading for the exit.
Cover the screed with a polyethylene film and leave it in this state for 12 hours.
After the initial hardening, knock off the identified mounds with a strong spatula. The whole surface of the screed is treated with a wooden grater, trying to obtain a uniform rough surface.
Begin the smoothing of the leveled surface. To do this, you need to prepare a solution of sand and cement brand "400" in the ratio of "one to one."When carrying out grouting surfaces, wet it with water from a normal household spray.
If you have lighthouse rails that limit the leveling surface - remove them at this stage, then fill the formed voids with an equalizing solution.
Leave the formed screed of sand and cement to dry. Full hardening of the screed made in this way occurs within 28 days.
Do not allow drafts to form when screeds dry. Also, keep fresh screed from direct UV rays. If the room is very hot, then at the initial stage of drying the screed must be covered with a polyethylene film for a day. Also, in hot weather, it is recommended to moisten the fresh screed twice a day with water.