Cracks in the floor screed: what to do if they appear and why they form

Rough finishing is an invisible but very important part of the renovation. The quality of its implementation determines how the final coating will look and how long it will last in its original form. Therefore, before starting finishing work, you need to make sure that the base is strong and reliable, and, if necessary, eliminate defects. If, after leveling, cracks appear in the floor screed, what to do with such a base must be decided on the spot, depending on the scale of the damage, the area of the object, and the type of finished floor covering.

Sometimes it is easier to redo a screed than to repair it Source homemasters.ru

Looking for the cause of the problem

To solve the problem once and for all, you need to find and eliminate the cause of its occurrence, otherwise it will recur. This also applies to situations where the floor screed is cracked - what to do with the cracks can only be decided after you understand why they appeared.

In general, on a surface finished with cement mortar, cracks often form due to the low plasticity of the material and its ability to expand and contract with temperature changes. Their occurrence can be avoided only by strictly following the technology of mixing the solution, preparing the base, installing the screed and fulfilling the conditions necessary for its uniform drying.

The slightest deviation in any of the above points is likely to cause cracking of the cement coating. Most often this happens in the following cases:

errors when mixing the solution - excess water or uneven distribution of components in the mixture;

Liquid solution has less strength Source strojlyuks.ru

insufficient screed thickness;
weak, sagging or vibrating foundation under the screed;
absence of damper joints or technological gaps between the screed and the walls;
uneven drying of the solution due to drafts, temperature changes or as a result of forced drying.

The listed factors refer to gross violations of the manufacturing technology of concrete floor screed, which may lead to the impossibility of restoring the coating using spot repairs. If it is covered with deep cracks over the entire area, crumbles underfoot or “breathes,” the screed must be dismantled and remade.

Dismantling a screed is a dirty, time-consuming and expensive job, so it’s better to do everything right right away Source amazonaws.com

If concrete was poured on an unstable sandy base, on a wooden floor or thermal insulation slabs, and the floor screed cracked, what to do: pour another layer on top with mandatory reinforcement with steel mesh.

Defects in a fresh cement coating may not appear immediately, so after finishing the work you need to wait at least 3-4 weeks and then carry out an inspection. To do this, tap the screed with a rubber mallet, revealing local delaminations of the concrete, and strips of thin paper are glued onto the cracks and left for 10-14 days. If after this time it remains intact, it means that the cracks are stable and will not deepen or expand. If the paper is torn, this indicates that the concrete layer is unreliable - it will continue to deteriorate.

How to prevent cracks from appearing in the floor?

If holes appear on the surface, and it doesn’t matter what you plan to do next - a self-leveling or warm water floor, then work should be suspended and this problem should be solved. We have already figured out how to do this. But, it is better not to fight troubles, but to be able to prevent them.

Measures to prevent the formation of potholes and holes on screeds include not only adherence to technology, but also reinforcement. It can be done using reinforcing mesh or fiber (polypropylene, steel or basalt). Reinforcement mesh is most appropriate when making semi-dry screeds. Its most optimal characteristics: rod cross-section 4 mm, cell 100/100 mm or 150/150 mm.

Is it possible to use reinforcing mesh together with fiber to prevent surface cracking? Certainly! This combined method will give your floor even more wear resistance and strength, and you will have confidence in the quality of your work!

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Making expansion joints

One of the main reasons for cracking of a concrete slab is the lack of compensation gaps around the perimeter of its abutment to vertical barriers - walls, columns, thresholds, etc. And in rooms with a large area, the screed can crack and swell during shrinkage and during linear expansion, if expansion joints are not installed in it, dividing the solid slab into several sections independent from each other.

The expansion joint allows the screed to expand freely Source tb.ru

See also: Catalog of companies that specialize in home insulation

Before repairing cracks in the floor screed, it is necessary to arrange all the necessary technological joints in it, otherwise they will appear again and again. And the sooner you do this, the better.

It will no longer be possible to create gaps between the floor and the wall using a finished screed. But you can cut the grooves as close to the wall as possible using a grinder with a large diameter disk or a wall chaser. If there are columns, a shrinkage seam is made around them, but not parallel to the edges, but in the form of a diamond, so that the corner of the column looks at the straight section of the groove.

If the dimensions of the room on one or both sides exceed 3-4 meters, the seams must be cut across it.

Note! The depth of the groove must be at least a third of the thickness of the screed, and the width must be at least 10 mm.

The finished cracks in the floor are cleaned of debris and primed. After the primer has dried, they are filled with polyurethane sealant or special mastic. After drying, these compositions retain elasticity, which will allow the cut cards to move independently of each other without transferring deforming loads.

Filling the seam with sealant Source stiagka-pola.ru

We repair the screed

How to repair cracks in a floor screed depends on the degree of deformation of the subfloor.

Sealing microcracks

Shallow, small cracks usually do not cause problems. They arise due to improper concrete drying conditions. If they begin to appear soon after pouring, the floors should be wetted and covered with film.

Very thin microcracks can be left untouched or covered with liquid cement mortar or tile adhesive. If the width reaches several millimeters, it is better to play it safe and seal such cracks to the full depth.

The crack is opened by cutting off the concrete on both sides of it with a grinder with a diamond blade, which is set at an angle to the crack.

If the amount of work is small, you can get by with a chisel and a hammer Source wp.com

Pieces of concrete and cement dust are removed from the resulting triangular furrow.
Its walls are well impregnated with a deep penetration primer.
After the primer has dried, fill the recesses with the solution, applying it with a small slide.
As soon as the solution sets, but does not completely harden, the excess is removed from the surface with a spatula.

If you immediately level the repair mixture over the surface, then during the drying process it will shrink and a depression will form.

Types of damage - mastering the first subtleties

Professionalism begins with assessing the nature of the damage and the amount of work to be done. The nature of damage can be of various types:

visible cracks of various sizes, potholes, pits;
concrete peeling off in places;
poor coverage of the entire floor surface.

Replacing the finishing floor covering or completely removing it will provide an opportunity to see the unsightly condition of the screed in all its glory. Weakening of the material, complete or partial peeling of the screed will indicate that poor quality cement was used during the work or the technology for preparing the required solution was generally violated. The increased formation of cement dust speaks eloquently about all this. Such signs of poor quality concrete work cannot be ignored. At this stage of damage, you can still get by with a small monetary investment.

Video description

How to strengthen concrete that is peeling off from the base is described in the video:
Having found out why the floor screed cracked and what to do, you can begin repairs.

First, by tapping, areas of delamination and voids are identified and marked with chalk.
In the marked places, holes are drilled in the screed at a distance of 15-20 cm from each other.
After cleaning and priming, an epoxy mixture is poured into the holes.
It also seals cracks.
After the mixture hardens, the holes are filled with liquid cement mortar.

It is important! This method cannot be used if a water or electric heated floor system is installed in the screed, or other communications without an accurate wiring diagram.

When drilling repair holes, there is a high risk of damaging the cable Source sense-life.com

Bubbling - what is it?

One of the common construction problems is heaving - the peeling of the final coating from the base of the floor. There are several main causes of swelling:

Lack of waterproofing. Before installing the self-leveling floor, at the screed installation stage, the base surface around the perimeter is insulated from moisture penetration. If the insulation joints were made poorly, then water seeps into the cracks and spoils the base, causing peeling;
Poor quality of screed and base components. There are branded GOST standards for installing floors; if the brand strength of the base is too low, the floor will sooner or later begin to peel off;
Pollution. Before installing screeds and self-leveling floors, all debris must be removed, otherwise swelling will be inevitable.

The heaving is eliminated by repairing the section of the self-leveling floor in the place where it occurred. First of all, the causes of detachment are determined and eliminated. For example, all moisture must be dried before starting repairs. After this, the problem area is dismantled and treated with a special impregnation with deep penetration.

Is crack repair always necessary?

Even experienced craftsmen cannot always guarantee that the cement screed will retain its solidity and integrity, since, despite its hardness and strength, it is a fragile material that is completely unable to adapt to environmental changes and withstand excessive loads.

In addition, having an impressive weight, the poured concrete slab under the final coating will not go anywhere, even if it cracks. It is not necessary to repair it if:

the cracks are small and rare, not prone to expansion;
when tapping with a mallet or walking along the edges of cracks, dust does not rise from them;
the base does not vibrate under the weight of a walking person;
Laminate, linoleum or other covering will be laid on the screed without rigid adhesion to it.

But in the case of finishing the floor with ceramic tiles, the diverging edges of the cracks can transfer stress to the tile adhesive and to the tile itself, hopelessly ruining the expensive coating.

A weak screed is the reason for cracking of tiles Source agromat.ua

So that there are no cracks

If you think in advance about how to make a screed so that it does not crack, you can avoid the hassle of repairing it. To do this, several conditions must be met.

The thickness of the screed at its thinnest point should be at least 20 mm, and if the base is sand, expanded clay or insulation boards - at least 30 mm.
When installed on a weak or shrinkage-prone base, the screed must be reinforced.
The screed must be poured over the entire area at once, without taking long breaks.
If this is not possible, arrange expansion joints at the junction of the dried and fresh mortar.
Observe the proportions exactly when mixing the solution, taking into account the brand of cement and the moisture content of the sand.
If, after leveling, puddles of water form on the surface, it means there is too much of it in the solution; it is better to immediately redo this area.
Avoid drafts during the first days of drying the solution.
As soon as the screed sets, cover it with film.
If the air in the room is dry and hot, periodically moisten the surface with water so that the concrete dries evenly.

Repair compounds for concrete

In order for the restoration of artificial stone to be successful, before choosing a repair composition, a thorough inspection of the destroyed structure is carried out and an analysis is performed. The mixture is selected taking into account the following factors:

the degree of loading of the structure, its load-bearing capacity;
depth of damage;
operating conditions of concrete (humid environment, temperature conditions, degree of exposure to aggressive environments);
accessibility to the damaged area;
expected scope of work.

If you are repairing the concrete surface in a visible area, it is important to take into account aesthetic requirements

Major Damage Repair

The large damaged area is filled with new concrete mortar. First, the surface of the structure is cleaned of loose pieces and dust. A clean, solid base of good quality concrete should remain.

Filling is carried out with a cement composition with complex additives that improve its performance characteristics. Good results are achieved by fast-hardening polymer mortar or fiber-reinforced concrete.

For concrete repair with cement mortar to be successful, it is important to create conditions for its reliable adhesion to the base being restored. Two methods are usually practiced:

Continuous filling of the entire area of the structure is carried out with a solution more than 100 mm thick. If partial restoration is carried out, the concreting site is deepened.
Better adhesion between old and new layers occurs when a steel reinforced mesh is attached with dowels to the base being restored.

Before pouring the solution, the surface of the structure being repaired is treated with epoxy, acrylic or other adhesive compounds that provide better adhesion.

Dry mixtures for concrete repair

All dry mixes for concrete repair contain cement, which ensures optimal compatibility with the concrete structure being restored. There are many compounds from different companies on the construction market.

Apply the repair composition in a layer 5-50 mm thick on horizontal and vertical substrates. To restore the ceiling, it is optimal to maintain a mixture thickness of 30 mm. Better adhesion is ensured by pre-treatment of concrete with a primer or primer.

concrete repair mixture OSNOVIT

According to the type of application, dry mixtures are divided into the following types:

for work at temperatures above +5°C;
at negative temperatures;
for waterproofing and providing protective properties;
for repairs that do not change the geometry and load-bearing capacity of the concrete structure.

The scope of application of dry mixtures is wherever quick repairs are required to eliminate defects.

Pros:

good adhesion to the old base;
high mechanical strength of the frozen composition;
due to additives, the mixture does not shrink;
possibility of eliminating defects up to 100 mm deep.

The disadvantage is the high cost and short shelf life.

Thixotropic mixtures

In essence, these are analogues of conventional dry mixtures, but with improved characteristics. Popular manufacturers are: MAPEI, BASF, Sika. The thixotropic composition for concrete repair is based on cement, sand, and complex additives. Mixtures with polymer fiber are considered the most effective.

Sika concrete repair mixture

The optimal layer thickness is from 10 to 30 mm. The mixture is used when repairing monolithic and prefabricated concrete structures, for sealing seams, and restoring protective layers.

Pros:

resistance to mechanical loads and abrasion;
good adhesion to the base;
resistance of the frozen composition to moisture and low temperatures.

The downside is the high cost and inability to use at sub-zero temperatures.

Epoxy and polymer compounds

The main purpose of the compositions is the repair of self-leveling floors, injection work, and the organization of protection of a concrete structure from the effects of destructive factors. Popular, "Technoplast", "KrasKO".

polymer composition for concrete repair Elakor

Sometimes the composition is applied to improve the adhesion of the base to the new repair layer. Polyurethane mixtures eliminate leaks and prevent the influx of water.

Pros:

resistance to mechanical and chemical stress;
good wear resistance;
high adhesion to the base;
good waterproofing properties.

The disadvantage is the short viability period.

Briefly about the main thing

Cracks in screeds are a frequent and poorly controlled phenomenon. They are formed even with strict adherence to the work technique due to uneven shrinkage of the material, which does not have plasticity. They don't always require repairs. But if the defects occupy a large part of the surface and tend to grow and increase, and the floor “breathes” underfoot, the cracks must be sealed using cement mortar, tile adhesive, sealants or epoxy resin, depending on the situation. It is also advisable to fasten the largest crevices with metal brackets in the transverse cuts.