Cement screed and its repair, assessment of the condition of the coating, preparation of the repair mixture and technology for performing work with various types of damage. Cement screed is the outer layer of the sub floor. Over time, for many reasons, it wears out, but the floor covering laid on top does not provide timely identification of the defects that have arisen. In the process of replacing it, when the base is exposed, the hidden problems of the floor become apparent, and it becomes necessary to repair the cement screed. You will learn how it works in this article.
Assessment of the condition of the cement screed
The floor screed is subjected to tremendous stress from the weight of the flooring, furniture and equipment, as well as dynamic effects from falling objects and walking by people. Therefore, the service life of an expensive floor repair largely depends on its condition. The money invested in this event can be wasted if a neglected screed makes itself felt.
Reliable information about the condition of its surface can be obtained only after complete cleaning of the floor from the old coating, debris and dust. To determine the degree of damage to the screed, there are the following criteria:
- The screed is even, but has small indentations, a network of small cracks and is constantly dusty. To eliminate such damage, an investment of significant funds is not required, since such work can be done independently.
- The surface of the base has delamination and in some places is covered with deep transverse or longitudinal cracks, but their average size does not exceed? the length of the short wall of the room. Such a screed can also be repaired independently, but this will require building mixtures with a special composition.
- The screed has significant curvature, expressed in numerous depressions and humps. To level such a surface, a milling machine will be needed, which creates a lot of noise and dust during operation. Therefore, the repair of such a foundation is recommended only in non-residential premises or private households. In city apartments, neighbors may not stand the discomfort from the work of technology, complain or go in person.
- The floor of an apartment located in a high-rise building is covered with large deep and long cracks that intersect with each other or are located along the diagonals of the rooms. Such repairs are very difficult and are carried out only by specialists after studying the nature of the loads on the floor and the bearing capacity of the structures of the house.
Redecoration of a cement floor screed is performed if no more than 30% of its area is damaged. In other cases, it is better to replace it completely.
Preparation of a repair mixture for a cement screed
Today the construction market has a huge selection of mixtures designed for the restoration of cement screeds. These formulations can have a variety of bases, including polyurethane and synthetic resins. Many of them are used to renovate industrial floors. But in an ordinary apartment, the use of such mixtures is not always rational, given their cost.
For a simple repair of a screed at home, a mixture that can be made independently from affordable and inexpensive materials is quite suitable. It contains PVA glue, water, sand and cement. To prepare a repair mortar, you first need to dilute the PVA glue in water in proportion to 1: 3, and then add a dry mixture of cement and sand 3: 1 to the resulting emulsion.
The composition should be mixed at minimum speed for 5 minutes using an electric drill with a mixer attachment. After the end of the process, it is recommended to immediately immerse the mixer in the water poured into the bucket and rinse well with the operating mode of the tool.
If the cracks in the screed are deep, such a composition will not work. To repair it, in this case, you will have to buy a special thixotropic liquid for concrete. Store-bought ready-made mixtures are mainly mixed with water, and home-made compositions are mixed with an adhesive suspension. Ready mixes can be replaced with tile adhesive.
Cement screed repair technology
All screed defects, such as shallow and deep cracks, peeling and dust formation, potholes and depressions, are eliminated in various ways, which we will consider below. In the meantime, the following tools and materials must be prepared for work: a perforator, a trowel and, as a rule, a brush, a trowel and a paint roller, cement, a primer for concrete and a repair mixture.
Elimination of minor defects
These include small cracks, gouges and chips on the surface of the cement screed. The reasons for these defects are mistakes made during its installation: the absence of expansion joints, poor-quality grout for pouring or insufficient reinforcement of the base.
To repair a cement-sand screed with small defects, you first need to mark all problem areas with chalk, and then cut each crack and recess with a hammer and chisel a few millimeters in depth and 1-2 cm in width at the edges. After that, you need to remove construction debris from the surface of the screed with a broom, and from the cracks with a vacuum cleaner.
Cracks and gaps should be treated with a penetrating primer several times until it is no longer absorbed into the concrete. This procedure is necessary to increase the adhesion of the base with the repair mortar.
While the primer is drying, you can prepare a mixture according to the recipe described above. The resulting solution should be filled with the cut damage of the screed just above the general level of the rest of the surface, and after the mixture has hardened, grind the repaired areas.
Advice! If the thickness of the screed is small, it is better to cut the damage to its full depth. In this case, the adhesion of the putty to the base will be better, and further development of cracks will become impossible.
Sealing deep cracks
Such damage to the screed must be cut to the full depth. For this purpose, it is recommended to use a circular saw and a hammer drill, it will be unproductive to work with a hammer and chisel.
After the crack is cut, several strobes must be made across it, the ends of which will extend beyond the resulting cavity by 5-6 cm on each of its sides. Then, holes 2-3 cm deep should be drilled at the two ends of each groove, and then remove the debris and clean the cut cracks with a vacuum cleaner. Prepared grooves should be primed and left to dry.
Now you need to prepare a mortar of sand and cement in a ratio of 3: 1. Filling the crack should be done gradually in several stages. In the first of them, a liquid mixture is used, which must be filled in a part of the cavity in depth so that it penetrates into the most inaccessible places of the excavation.
Then you need to prepare a solution of medium density and fill the crack with it flush with the bottom of the transverse grooves. When it hardens, it is necessary to make staples from thick wire or reinforcement to tighten the crack and mount them in the grooves so that the bent ends of the rods go into the drilled holes.
After that, a little plasticizer must be added to the solution and filled to the end of the cavity along with the staples. Then the surface at the site of the former crack must be leveled, and after the solution has dried, it must be sanded. Now the repair of the crack in the cement screed can be considered complete.
Restoration of screed detachments
Delamination and even swelling of the screed occurs when it is laid on a dirty and not primed floor. Such defects can be detected using a light hammer or piece of reinforcement. To do this, it is enough to tap the surface of the screed with this tool and determine the place of the defect by the dull sound of the impact. When the screed peels off, gaps may appear through which, with this diagnostic method, clouds of dust will fly into the air.
Detachment repair can be done in two ways. In the first case, the entire damaged area must be cut out, and a new screed must be laid in its place. In the second, the exfoliated area is injected, during which a special binder based on an epoxy or adhesive base is introduced under it. The second method is less laborious and faster. It makes sense to use it if the problem area is flat and does not have through cracks.
After determining the places of screed delamination, they need to be outlined with a marker or chalk, then take a hammer drill or drill and install a drill or a concrete drill with a diameter of 16 mm in any of these tools. Drilling in places of delamination should be carried out for the entire thickness of the screed, observing the distance between them 0, 2-0, 3 m.
When this work is completed, a primer must be poured into the holes obtained. He must wet the entire internal cavity between the base and the screed layer. To make the process of drying concrete faster, you can use a construction hairdryer.
It is important to correctly identify the screed injection material. It must have good fluidity, because the repair mixture will have to be pumped under the screed using a plunger pump or a construction syringe. A cement-glue mixture will cost less, a low-viscosity epoxy resin is more expensive, but more reliable.
Injections through the holes in the screed must be carried out gradually, giving time for the repair compound to fill the entire space of the cavity. This procedure should be continued until the mixture appears on the surface of all drilled holes and its level does not stop dropping.
The screed must dry for 24 hours. After that, you can work with it further: priming, gluing linoleum, laying tiles, etc.
How to repair screed potholes
This damage occurs due to a violation of the technology of the screed device and significant loads on the base. In the presence of such factors, during the operation of the floor, voids appear in the screed. They are more dangerous for the floor covering than cracks. In the areas of potholes, the floor suffers a subsidence and deforms, which leads to its further complete destruction.
In this case, for repair, it is first necessary to cut through the pothole with a "grinder" equipped with a diamond disc, along the perimeter of the damage to the entire thickness of the screed. Then, using a hammer drill or chisel and hammer, remove the concrete from the pothole. After that, the cavity must be cleaned of screed residues and dust, and then treated with a penetrating primer.
After the primer has dried, it is necessary to prepare a repair mixture and fill the pothole with it using a spatula. Without waiting for the mixture to dry, use a wide spatula and lath to level it to the floor and leave until the final polymerization. Grinding the problem area should be done so that the pothole filled with the mixture does not stand out against the background of the floor.
Important! If the depth of damage is more than 5 cm, the repair mortar should be applied gradually in several steps.
Repairing a dusty screed
Over time, cement-sand dust begins to appear on the screed. This is especially evident in those rooms on the floors of which the screeds serve as a topcoat, for example, in the basement, garage or any other utility room.
Gradually, the amount of dust increases, and it becomes impossible to simply sweep it away. It is often the result of significant mechanical loads on the surface of such a floor and its "old age". In other cases, dust appears immediately after a month or two after starting to use a new screed. The reason for this is the low quality of the cement mixture and violations in the technology of its laying. If it is not possible to replace the tie, it can be repaired in the following way.
First, you must thoroughly clean its entire surface with a vacuum cleaner. If at the same time potholes and cracks are found, they must be repaired using the above technology. After that, the screed must be sanded and cleaned again in the same way. The floor surface should then be treated with a penetrating primer and allowed to dry. At the final stage of work, the entire screed must be covered in two layers with a polymer composition. If the room has high humidity, special water emulsifiers must be used for this purpose.
There is another way to eliminate screed dust - painting it. In this case, the coating must be sufficiently wear-resistant; according to this parameter, the finishing material should be chosen.
The cardinal method of such a screed defect is its reinforcement with fiberglass and subsequent pouring with a special self-leveling building mixture. To implement this method, the floor surface must first be cleaned with a vacuum cleaner, primed and allowed to dry.
After that, glue should be applied to the surface of the screed and the fiberglass should be overlapped. When the first layer of glue is dry, the second layer must be applied to the resulting coating and allowed to completely harden. The floor can then be sanded or poured over the fiberglass fabric with a self-leveling compound.
How to make a cement screed - watch the video:
Any do-it-yourself work to repair a cement screed floor is not particularly difficult and does not require professional knowledge. Some tools for their execution, for example, a hammer drill, can be rented, while others can be purchased for the future for personal use. A high-quality floor repair is more profitable, since it can last only a few days, and a complete replacement of the screed will take a month. Good luck with your work!
