Of course, any phenomenon has objective reasons and preconditions, which we will consider further.
Often, to explain why the floor screed cracks, there are two reasons:
- Poor substrate. Here you can list the non-uniform texture of the base under the screed, its insufficient thickness or other deviations from the norm. In these cases, the screed begins to crack and burst, and to correct the situation in any way will not work. The only way out will be the dismantling of the concrete layer and the organization of the basis according to all necessary standards.
- Faults in the pouring and poor quality of concrete screed. In this case, if the screed is cracked, it can still be recovered.
To understand why the screed cracks, it is important to determine what exactly the rules were violated when pouring it, and how to avoid noncompliance in the future.
The main types of deficiencies
As already mentioned, the likelihood of flaws on a new screed is quite high. This is due to the fact that it is difficult to achieve optimal conditions for curing concrete.
To form with the methods of struggle, it is necessary to know what types of flaws are referred to. Then you can determine how to fix them.
- Small cracks of up to 15mm. In most cases arise from uneven drying. For caulking, you can use ordinary tile glue.
- Cracks more than 15 mm. Make a good restoration will not be easy, thanks to this experts recommend doing a new screed on top of 3-4 cm thick. But it should be taken into account that a similar method of elimination will reduce the effectiveness of underfloor heating.
- Concrete frizz. Often, because of the moving structure of the base can appear bloated areas on the surface. In these cases it is necessary to scrape off these areas and fill the dents with cement.
- Differences up to 5 mm. If the surface is uneven, you can remove them with a grinder, and the dented areas filled with tile adhesive or cement mortar of grade M300 or M500.
- Large cracks, up to 2 cm. This type of defect can often occur due to the lack of expansion joints. You will need to seal them with sealing adhesive or cement mortar.
Broken screed warm water floor consequences
Most masters say that a narrow, small cracks are allowed in the screed floor in a new apartment and with it does not need to do anything. In most cases, this is not the case. The question arises as to what is the reason that it cracked? Such defects can arise from improperly poured or unstable foundation, and if you do not eliminate these defects pour a new screed or fix cracks in the old one, the foundation will continue to deteriorate. The next step will begin to crumble concrete on the edges of the crack, then the finishing layer will begin to crumble, then the skirting boards. And you have to do the whole repair again. So the first thing you need to know why a screed in a new building and what to do what to do so the cracks did not go further?
As any twist screed floor the best, and sometimes almost the only way to level the base under the finish coating. It makes a smooth and even surface for laying the finishing layer, hiding under its thickness communications or any defects in the foundation. But when filling it, some people face such minor difficulties as preparing the correct mixture or put not right beacons for floor screed. Just these little things and lead to unwanted cracks when the screed dries up. But do not despair! Sometimes, sealing cracks in the screed floor is not such a difficult task. Let’s discuss with you the reasons why the screed may break and how to avoid it. And if you can not avoid it, consider this specific example than to patch cracks in the screed floor.
- The manufacturing technique is flawed
- Incorrect proportions of ingredients in the mix
- Poor quality or small amount of cement in the mixture
- No expansion joint
- Incorrect reinforcement
This is the most common cause of cracks in the floor screed. It usually comes to light in ready mixes. First of all the risk group includes people who decided to do it for the first time, goes to the store and buys a ready-made dry mixture. Manufacturers of dry mixes in the production calculate the exact amount of additives that are dissolved in water, homogeneously distributed between each other.
You probably know that the liquid mortar is better to be applied to the floor, and beginners will surely have a desire to add a little water. Such a move will only make the quality of the mixture worse in the end. What the manufacturer wrote on the package of mixtures should be strictly followed according to the instructions.
It is not recommended to mix a mortar by hand, for this purpose a construction mixer is more suitable, and if you do not want to splurge on this expensive wonder of technology, you can buy a simple nozzle on the electric drill and at low speed to make a homogeneous mixture.
For quality screed it is recommended to take a medium-grained sand quarried rather than river sand, which is more accessible. The optimal type of cement will be M-400. The first thing the sand is sifted from lumps of clay and pebbles. Water is added by eye, until the mixture has sufficient viscosity and plasticity.
If this minimum condition is not met, cracks are more likely to appear.
A large amount of water in the concrete will subject it to shrinkage or deformation. In this case, the screed is also likely to crack. Flooding of the concrete mixture also reduces the strength of the finished product (screed). In simple words, the screed is not strong enough and the surface will be loose.
In this case, the screed will need to be covered with a primer of deep penetration, to avoid dusting and sweeping after laying the final coating. And this again is unnecessary costs.
The second common mistake is a different material of screed and screed itself. Plaster on a gypsum basis rarely gives rise to shrinkage after drying, which cannot be said about the cement-sand mixture. And since between the installation of beacons and pouring screed passes a little time on the screed surface will get either depressions or bumps.
They do not arise only from the different compositions of the gypsum mixture of beacons and cement-sand screed., but also differences in plasticity, coefficient of linear expansion and adhesion. And in those places where the cement mortar adjoins the gypsum lighthouses, there may be cracks in the floor screed, well, what to do. We will have to fix everything.
Another gross cause of cracks in the screed is the improper location of expansion joints or their complete absence. Namely the wall joint and intermediate joints on the floor.
Wall expansion joint should be filled with elastic material (foam, plastic foam), to pass through the whole thickness of the screed, thereby separating it from the influence of deformation loads of the walls. Some craftsmen also recommend laying expansion joints around columns, built-in furnishings and stairs.
Intermediate expansion joints, on the contrary do not pass through the entire thickness of the screed, and only half. They divide the screed into equal shares, preventing it from cracking after shrinkage. The width of these joints is selected depending on the thickness, and the presence of underfloor heating. Do not forget to make special marks in the reinforcement mesh area if you have a reinforced screed.
Compensation joints are provided in all types of screeds in areas larger than 30 m? Accordingly, the maximum area of the fields into which the screed should be divided are the same 30 m? The sides of the area should not be more than 6 m. In due course, intermediate expansion joints must be cut in corridors, and the distance between these types of joints must be less than six meters.
If as the final coating is selected ceramic tile or porcelain then the notches from the expansion joints should be comparable to intertile seams.
Inside the joints are left unfilled, but the joints on the street are recommended to seal with silicone or waterproof adhesives to avoid water entering them and at sub-zero temperatures will not tear your screed.
Wall joints can usually be left empty. In the event that you decide to patch them it is recommended to use only soft materials.
Another common mistake that cracks screed is the wrong, poor quality reinforcement. If you decide to buy reinforcement and make a quality base, it must be in the body of the concrete and not lie under the thickness of the screed. Apply reinforcing mesh is not recommended here, and simply there is no reason to transfer so much money for nothing, but fibroarming will be very effective. Reinforcement should be in the body of the concrete, but do not lie under the screed. By and large, the use of reinforced mesh makes no sense. Much cheaper and more effective will be fiber reinforcement.
Not a problem if the cracked screed, but the beginning of rehabilitation work, you should perform a number of procedures to simplify and accelerate the work to eliminate the crack.
How to repair screed cracks quickly and easily?
- The first thing to determine for what reason they were formed. If you do not perform screed, determine the presence of expansion joints and how the floor was filled.
- If the cracks in the floor screed look like a few scattered along the base they are repaired with epoxy adhesives using the “force mending” technology.
- If the cracks in the screed floor heating appeared because of the lack of expansion joint between the rooms or along the walls, you should not fill them up without making this very joint.
Before starting the repair work should first identify the cause of the cracks. Otherwise, after a few months, they will again make themselves felt, not only in the old, but also in new places.
Before you eliminate cracks in the screed floor, you will need to see what the degree of damage and highlight areas that need repair.
You can easily find visible cracks. But hidden voids are to be found by pounding the entire base with a wooden mallet.
If during this procedure you will hear a ringing sound, then you have found one of these voids. Found hidden flaws should be marked and at the end of the work to calculate the area which requires repair.
If in the end it turned out that 30% or more of the room needs repair, it is recommended to dismantle the old base and pour a new coating.
Minor cracks in the floor screed is recommended to saw through with an angle grinder to 20 mm. After treatment remove trash with a regular vacuum cleaner and wipe the remaining dust with a damp rag and let the surface to dry before repairing. Once dry, the surface is ready to be repaired.
Trick!If the room is uninhabited, it is recommended to check the cracks for possible subsequent deformation. To do this, cracks in the floor screed are taped over with sheets of paper and left for some time. If the sheet ruptured, it turns out the crack continues to expand and repair requires a heavier approach.
Not without reason crack is one of the most severe damage to the screed, so the repair of cracks in the floor screed should be done here and now. If you do not pay attention to it in time, then most likely it will grow, which will lead to the impossibility of repair and will have to do a new screed.
- First you need to penetrate the crack with a diamond disc. In the end, you will have an even, not crumbling edge.
- Do not forget to remove all the resulting dust. with a vacuum cleaner, otherwise the adhesion of the epoxy repair composition will be bad and nothing will work.
- Across the crack you must saw a necessary number (determined by the length of the crack) perpendicular notches, the depth of which should be at least 2 cm, and a width of 20 cm.
- After that, prime the resulting surface, preferably with the addition of quartz sand.
- Pour the prepared mortar into the crack, up to half of it, and place the iron staples in the grooves. Once the filled part of the mortar starts to set, fill it up to the end. As everything dries you can start sanding.
That to eliminate cracks in the screed floor need to make not small expenditures, both financial and physical. Therefore, we recommend you to follow all of the above mentioned technologies and clearly follow them, then the repaired floor will serve you for a long time and you will not have to take up his repairs again.
To avoid repair work after drying, it is sufficient to follow the technology of screed laying. Let’s summarize: First of all we must observe the proportions of the mixture. Excess water will give us 100% cracks in the dry floor. The preparation of the substrate also plays a large role. If it will absorb moisture. the screed will need to be reinforced anyway.
And most importantly! It is not necessary to accelerate the drying of the mortar by artificial draughts or heating the room. In such actions, the moisture evaporates unevenly and quickly, this will also cause cracks.
Screed on the floor must dry out by itself, gradually and at the same temperature. If the weather outside is hot or windy, it will need to be moistened, thus protecting it from rapid drying. To carry out this process, it is mainly used wet burlap.
Observing these simple rules for filling the screed, you will never have cracks on your floor
The screed is usually a layer of cement-sand or concrete mortar, which allows you to level the floor slab, give it extra rigidity for subsequent installation of flooring. Lay pipes or heating cables in it, which form a kind of floor radiator during the operation of the system. The main function of the screed on the warm floor (water or electric) is to protect the communications laid from mechanical damage. In addition, the concrete or cement-sand layer forms a slab that evenly distributes heat throughout its area of the room.
The appearance of cracks on the surface of the wet screed for a warm floor. a common problem that often occurs with a violation of technology. If they are few, they are thin and are near the beacons or laid communications, it is not critical. But when the cracks are deep, and when you hear a dull sound when tapping, most likely there was a delamination. You can not ignore the situation: after the installation of flooring (laminate, tiles), the face layer will be damaged very quickly. This means that repairs will need to be done from the beginning. That is why it is necessary that the screed for a warm water floor was performed competently, in compliance with all technological requirements.
- Poorly prepared floor (weak spots, cracks, dust or sand from the surface have not been removed).
- Poor adhesion to the substrate (the mixture is poured thinly on the wooden floor without proper preparation).
- Absence of a membrane film.
- Inconsistency of the recipe.
- The thickness when pouring is uneven.
- Dry mixture is used, which is designed for screeding without heating elements.
- Pouring the mortar too thinly.
- Gypsum or Rothband screeds are used (because of the difference in plasticity of concrete and gypsum, cracks are always formed at the joint).
- No base reinforcement, fiber is not used in the mortar, when heavy loads are expected.
When choosing you should pay attention to the semi-dry material. When using it, shrinkage will be minimal, provided that the base and mortar are prepared correctly. The only significant disadvantage will be higher cost and the need to use a concrete pump to apply the composition.
In accordance with the recipe, dry ingredients should be mixed until homogeneous. Then you need to make a crater in the center and pour water in portions, strictly observing the proportions. The basic composition includes:
To increase the strength of the screed should add plasticizer, provided that it has no property air entrainment.
Important! Prepared concrete should not release water in the process of pouring.
Screed Expansion Joints Underfloor Heating. Do you need expansion joints in your screed?
The thickness of the screed is determined individually. At the same time laid under it the system of pipes in its performance should be able to quickly heat the coating and give the heat into the room. In this regard, the thickness of the slab is on average 25. 45 mm when using self-leveling ready-made materials. If the work is carried out with concrete slurry, regardless of its composition, the screed must be 5.5 to 6.5 cm. In accordance with the requirements of SNIP thickness over the pipes should be 4 to 5 cm.
For electric systems, the thickness of the screed is determined primarily by the capacity of the heating element.
Most often, if the question arises about what screed for a warm floor is better, many will choose the cement-sand version. The main argument in its favor is a relatively low cost and availability of all the necessary components. For the filling should use the following composition:
The following proportions are recommended: 50 kg of cement/200 kg of sand. Then, in order to obtain a solution, you need to add about 1.5 liters of water. For plasticity, 150 ml of liquid dish detergent or soap are often added to the mass instead of plasticizer. As a result, the optimal composition for the work when laying should hold its shape, but align easily. It is important that it is not liquid.
Semi-dry screeds due to low water content have a relatively short curing time. Thanks to the use of a complex of additives their operational characteristics (especially strength) are higher in comparison with any of the compositions for the wet laying. In order to prevent the formation of cracks, mineral fibers are additionally introduced into the base material. To walk on such screed is possible already in 12 hours, the full hardening of the majority of such mortars (Dauer Grosser, Starateli, Unis Horizon) is up to 1 week.
To prepare such a mixture for a warm waterborne floor is very simple: it is sold fully prepared or requires only the addition of water in the amount indicated on the package. The algorithm of the work is as follows:
- Set beacons on the prepared base with a spacing of 1.5. 2 m.
- The prepared semi-dry mixture is spread on the surface and smoothed over the entire area with a rule.
- To finish smoothing it is used a trowel or a spatula.
Important! The material prepared (diluted with water) should be used for a maximum of 1.5 hours. Do not allow intensive drying of the screed during the curing period (it is necessary to protect the screed from exposure to draughts, intense sunlight).
The technology of installation of the system on the example of the concrete screed
- Lay the polyethylene film on the prepared surface (after dusting and grouting cracks).
- Installation of the thermal insulation layer (mineral wool or polystyrene). Its thickness can be from 50 mm in case of a cold ceiling and from 20 mm if the room is located above the heated room.
- Spread the heat reflective foil.
- Laying of pipes according to the system design.
- Lay the reinforcing mesh.
- Walls are glued with damping tape.
- Installation of wooden formwork (it must not press on the pipes).
- Installing screed.
- Screed preparation and filling.
- Laying of expansion joints (you can use wooden battens, which must then be removed).
- Smoothing the concrete layer.
- Removal of air bubbles, which are formed throughout the thickness of the screed during the pouring, with a needle roller.
- Once fully cured, you can floor it and use the heating system for its intended purpose.
Important! After laying the pipes before pouring the screed, you should draw their location with an indication of the exact size, in order to later facilitate the repair and maintenance of the equipment.
It will be interesting to see: “Pouring the cement screed for a warm floor”.
When complying with the technology of works at each stage of installation, regardless of the technology used (wet or semi-dry), will provide high strength and durability of the structure. In most cases, the choice is based on factors such as time of readiness for further installation (if the complete drying of concrete mixture will take about 1 month, then using semi-dry technology installation of finishing material can be performed in 1-2 days).
The question of what mixture is better to fill the water underfloor heating can also be solved by focusing on the characteristics of the room. For example, if the interfloor ceilings have large cracks or holes, wet technology should not be used, in addition to technical problems do not have trouble with the neighbors. In the case where the room needs additional insulation, it is better to choose the cement-sand version. In any case, before you buy building materials, pipes, other necessary equipment, you can always consult our experienced specialists. He will be able to resolve all doubts, make the best choice, call!
Causes of occurrence
First of all, we note that technically the floor screed cracks in two cases:
- Problems with the substrate. Unevenness, small thickness and other inconsistencies of the substrate lead to fractures in the coating. In this case, we will not be able to restore it. Only a complete removal and bringing to the required standards of the basis itself will allow for quality grouting.
- Poor quality of the screed itself as a result of errors during installation. This is what we will deal with.
In order to effectively eliminate cracks in the floor screed and prevent their appearance in the future, consider non-compliance with the rules on pouring concrete, which leads to them.
Expansion joints and edge tape are missing
In the cement mortar during curing occurs uneven shrinkage processes.
One of the most telling examples is the appearance of the crack on the threshold of the doorway. The width of this area is less than the rest of the room, so it dries faster, experiencing mechanical stresses of the neighboring rooms.
Such deformation is not particularly harmful, it may well be eliminated by the finish coating. But, if expansion joints were created, it would not appear at all.
It is also very important to use a damping tape for underfloor heating. Many even experienced professionals discard this point, but in vain. The cast mass of concrete, when it hits the wall during expansion, can both damage itself and cause significant damage to the side slab.
Tape, however, having a thickness of one centimeter, is glued on the perimeter of the entire room at the level of the finishing layer of the filling and compensates for all the possible shrinkage of the mortar. Given that its price is low, especially in comparison with its usefulness, its use should be mandatory.
Tip: If there are columns in the room, they also need to be covered with edge tape, as the deformation of the cement layer will also be directed to them.
In the case of a large coverage area, create a grid of joints with a spacing of five meters. Cut them with special equipment, in an extreme case “angle grinder”. Their depth should be about one-third of the thickness of the layer.
Observing such simple rules will prevent the problem itself.
Excess or lack of water in the solution
This applies to the use of ready-made dry mixes for floor screed. The fact is that the packaging indicates exactly how much water is needed to dissolve special additives and distribute them evenly throughout the mass.
Since a thinner mortar is easier to apply to the substrate, newcomers always want to add more water. But it will significantly worsen the final quality of the mixture. Instructions on the package must be followed precisely.
Tip: Do not mix the mortar by hand, use a construction mixer or an electric drill on low speed. Otherwise uneven stirring can also ruin its properties.
Example of an electric construction mixer
The wrong thickness of the coating
- A smaller thickness leads to premature failure of the screed under the influence of external loads.
- Great thickness is covered with a network of cracks, while providing resistance to the evaporating excess moisture.
There is a very important rule to remember when working with concrete mortars: the longer they are in contact with water, the stronger and more reliable they are.
In order to solidify a longer and of higher quality we cover the screed with a polyethylene film and sprinkle with water with our hands during the drying period.
Special quick-drying floor mixes do not need such care, but they should not be left out in bright sunlight, for example.
Why Has My Screed Cracked? Don’t just try to repair it, you need to investigate why it happened!
Causes of cracks in screeds when drying
To prevent cracks in the cement screed, you need to properly dry it.
Before making a layer, you need to determine the load on the floor and choose an appropriate brand of cement.
If heavy equipment or furniture is expected to be installed on the floor, the brand of cement for preparation should be taken higher.
Screed must be poured in accordance with all the requirements and rules.
Why is the floor screed cracking when drying, you can find out by examining some of the recommendations needed to use when drying screed:
- Moisture and temperature abuse. The recommended temperature for normal drying screed. 15-25 degrees. If the temperature is over 25 degrees, you should sprinkle the floor with water until it has hardened completely. 28 days.
- Covering with polyethylene. After the cement screed has been soaked in water to keep it moist, it should be covered with plastic wrap.
- No walking on the screed. On the cement screed can walk only on the third day, for this you must lay planks and move strictly on them. No building materials and no loads should be placed on it.
- Limit ventilation. For normal drying, as soon as the mortar is laid, it is necessary to close windows and doors in the room to prevent drafts that contribute to cracking.
- Shrinkage of the house. New homes always shrink, so the new screed may crack after it dries. The shrinkage process can take up to one year.
To avoid watering screed every day, you can, after watering it and covering it with a film, fill the surface with wet sawdust or sand for better moisture retention. This is done 3 days after pouring, when all the beacons are removed and the holes after them are sealed. Under polyethylene screed should be at least two weeks.
Cement-sand screed practically does not give shrinkage, so if you followed all the rules for filling the floor, it should not crack. Such a surface is durable and does not require additional care.
How to strengthen the screed from cracking?
If you want to avoid problems and do not resort in the future to the repair work with the screed, you simply need to follow the technology of its laying. The quality depends primarily on the proportions of the composition. If there is an excess of water or cement you are guaranteed to form cracks. The quality of the base is also important. If its surface is unreliable or strongly absorbs moisture. the screed must be reinforced.
Another important point. the drying of the mortar. Most people try to speed up this process and start arranging draughts or heating the room. This causes uneven and too rapid evaporation of moisture, which also leads to cracking. Sand-cement mortar should dry out gradually at normal temperature and humidity, in addition, in windy and hot weather they should be moistened and protected from too rapid drying. Wet screed is usually used for this.
- Cement floor screed with their own hands Cement floor screed with their own hands is prepared first and foremost to level the rough floor. For laying an even screed, it is necessary to install beacons
- Semi-dry floor screed with fiberglass Semi-dry floor screed with fiberglass is a great alternative for reinforced mesh, because the addition of polypropylene fibers allows you to make three-dimensional reinforcement.
- Equipment for floor screed Nowadays, many owners prefer to do semi-dry floor screed, which is more reliable and economical. Equipment for floor screeding, as a rule.
- Calculation of materials for floor screed In the process of repairing and installing the floor, many home masters wonder how to calculate the materials for floor screed
- Composition of the mortar for floor screed Floor screed. not easy and requires masters to follow all the rules and observance of special clarity. The composition of the mortar for screeding.
- How to level a concrete floor with your own hands As a rule, those who are going to do major repairs or build a house wondering how to level a concrete floor with their own hands. To do this.
- Filling the floor with expanded clay The filling of the floor with expanded clay is very simple in its technology, so it can cope even a layman. The only point that is important to consider.
Why the cracks in the cement-sand screed and how to patch cracks with their own hands
Often after you have made a cement-sand screed, it can go cracking. After some time, but often not immediately, usually this process is manifested in 2-3 weeks. This process can be and not notice, in fact in 2 weeks many already lay a laminate floor, it is possible to do, provided that the screed dried up and no longer gives out a moisture. You can check this by covering the screed with a plastic film and leaving it for a day: if the film is not sweaty, then everything is good and you can start laying laminate flooring before the screed cracks 🙂 To begin with, let’s look at why the cement-sand screed cracks, then determine what kind of cracks you have, and then we will learn how to seal a crack in the screed with their own hands and prevent their appearance. : 1. Why a cement-sand screed cracks. 1.1 Screed Thickness Cracking. 1.2 Screed on thermal insulation without reinforcement. 1.3 Failure to observe the drying conditions. 1.4 Cracks in the beams and breaks. 1.5 Overwatering. 2. Determining the nature of cracks and their causes. 2.1 Screed cracking. 3. What to do if the screed cracked, how and what to patch cracks with their own hands. 3.1 We widen the gap angular grinder, caulk with epoxy and mortar. 4. Do you need to seal cracks? 5. How to prevent cracks in a screed.
Working mixes contain cement. It gives an alkaline reaction when in contact with water, which requires skin and eye protection. If the composition gets into the eyes, they are immediately rinsed with water and resort to medical attention.
The work is carried out only by qualified personnel, trained and medically certified. When interacting with the electric tool, its operability and grounding must be checked in advance.
Causes of defects in the form of cracks
It is interesting that the cement mixture has little plasticity, adhesion and a fairly high coefficient of linear expansion.
Why a floor screed can start to crack? In fact, the preconditions for the appearance of defects on the roughing base, quite a lot. As practice has shown, cracks, potholes and dents can appear even if the mortar has been professionally poured. What this may be due to? It is worth noting in advance that in most cases defects can appear already after the installation of cement screed. When laying gypsum and semi-dry mixes, cracking of the coating is much less common.
Hollows and peaks in the roughcasting may appear after the removal of beacons. The reason for the appearance of defects will be hidden in the physical and mechanical properties of the material used. Cement mixture has a low level of plasticity, adhesion, and a high coefficient of linear expansion. For this reason, even if very little time passes between the installation and removal of beacons, it will inevitably lead to the appearance of small cracks and holes.
What are the main causes of defects on the surface of the screed?
The wrong mortar was mixed, in which the concentration of water would be too high.
Causes of the formation of flaws, namely the fact that the screed of the floor of the rough base, can be very different, and will not be limited to the list presented. In addition, the quality of the concrete coating can be affected:
- Improperly installed waterproofing and thermal insulation.
- Poor-quality cement-based mixture.
- The mortar is not homogeneously prepared.
- Lack of required tools for pouring and leveling concrete.
- Failure to comply with the proportions when preparing the working composition.
Let’s take a look at the best things to do during the floor repair process.