Why does the floor screed crack when drying and what to do in this case

For anyone involved in construction or renovation, floor screed cracks can be an annoying and frequently perplexing issue. When the concrete dries, cracks start to appear, despite your high expectations for a perfect, flawless finish. In order to stop it and deal with any problems that may come up, it is essential to understand why this occurs.

Floor screed cracking during the drying process is caused by a number of factors. Inappropriate blending is one frequent cause. Excessive shrinkage caused by an excess of water in the mixture can result in cracks during the drying process. Environmental factors that can cause the screed to lose moisture too quickly include high temperatures and rapid drying.

Furthermore, the base layer may be very important. The substrate may move or be improperly prepared, which could result in the screed cracking. Furthermore, the absence of expansion joints may cause stress in the screed, which could result in cracks. To allow for the material’s natural expansion and contraction, these joints are necessary.

Don’t worry if your floor screed starts to crack; there are fixes available. The first step is to evaluate what is causing the cracks. Once found, you can take the necessary action, like modifying the mixture, enhancing the curing environment, or adding mesh or fibers to reinforce the screed. Identifying and resolving these problems will enable you to have a floor that is resilient and free of cracks.

The main reasons for cracking the screed

Even expert floor pouring can result in a cracked screed because flaws can arise from breaking down the guides (beacons) or from several other causes.

Incorrect proportion of mixing components

The reason this issue arises most frequently is because of the store-bought ready-made concrete mixtures. The truth is that precise calculations are made to determine the precise proportions of the components and water added during the creation of these compositions. However, any inexperienced builder knows that applying a liquid solution to the surface works best, which is why many don’t follow the precise ratio given in the instructions.

Cracked screed is the result of the concrete shrinking and deforming due to an excess of water in the solution.

Lack of expansion joints

If the area of the room exceeds thirty meters square feet, expansion joints must be made. These joints are filled with polyurethane foam; if the area is outside, silicone is used. They allow for a significant reduction in the load coming from the walls. In large rooms, the lack of these seams causes the screed to deform.

Incorrect reinforcement

When discussing the reasons behind floor screed cracking, it is important to take note of a relatively common error: inadequate reinforcement. In actuality, some inexperienced builders place a layer of reinforcement beneath a thick layer of concrete, whereas the reinforcement needs to be precisely positioned within the screed’s "body." It’s also important to keep in mind that employing a reinforcing mesh won’t give you the best results; instead, experts advise utilizing less expensive fiber that is mixed right into the cement-sand mortar.

Apart from the primary mistakes, numerous other mistakes are made during the process of creating and curing the concrete base, which have equally dire outcomes.

Other reasons for screed cracking

Defects on the floor screed arise from the following mistakes:

1. The solution was poured in violation of the temperature regime. In order for the composition to dry properly, the room temperature should be from +15 to +25 degrees. If the room is too hot, the screed must be watered every day and covered with polyethylene for the first 28 days.
2. The wet screed began to be pressed (you cannot walk on the uncured base or place building materials on it).
3. Ventilation was not limited (immediately after curling the screed, all windows must be closed).
4. Alignment was done in a new house. During shrinkage, the screed cracks, so it is not recommended to pour it earlier than a year after the construction of the building.
5. The height of the screed does not meet the requirements. It is worth considering that the thickness of the slab should not be less than 30 mm (provided that it is laid on a layer of expanded polystyrene). If you used expanded clay as an underlay, then the height of the screed should be increased to at least 50 mm.
6. A special damper tape was not laid along the walls.
7. The screed is laid too thinly over the communications.

Although it is advisable to identify the cause of the wet screed cracking before leveling the floor, errors can still be fixed if they have already been made.

What is needed to repair the screed

The following supplies and tools must be ready before you begin the "reanimation" of the leveling base:

• grinder and hacksaw for metal;
• perforator;
• metal rod;
• hammer;
• construction syringe;
• epoxy resin;
• quartz sand;
• primer.

Following that, you must identify the kind of cracks and perform repairs.

Finding visible cracks is fairly simple, but a wooden mallet is required to locate hidden voids. Use it to gently tap the base. There is undoubtedly empty space in places where the sound gets louder.

Crucial! It is best to remove the inappropriate base and install a new slab if a visual inspection and tapping revealed that more than 30% of the surface was damaged.

Following this, you can start working on the repair right away.

Removing small cracks

Using a chisel and hammer, microcracks less than 15 mm in diameter are expanded to a depth of 1 cm. This should cause a groove to form that narrows towards the bottom.

The resulting cracks need to be cleaned using a vacuum cleaner or sandblasting machine before being treated with a 1:10 mixture of "epoxy" and solvent. Moreover, tile adhesive is an option.

The groove is filled with mortar, cleaned, and sanded once the surface has dried.

Removing large cracks

More than two centimeter "pits" can be extracted in the following ways:

1. Deepen the crack to 5 cm with a grinder.
2. Using a chisel, make grooves on both sides of the crack and remove all the concrete.
3. Cover the surface, cleaned of dust, with "epoxy".
4. Fill the crack with concrete mortar in several stages.
5. If the damage is too big, then first make several cuts 2 cm deep and 1.5 cm wide across the crack. Then fill the resulting grooves with concrete and secure them with metal staples.
6. Clean and sand the surface after the solution has hardened.

Practical! You can look for further deformation in the cracks if the room is still empty. Place regular paper sheets over the grooves, allowing them to stretch, and allow to cure for a few days. If the paper is cracked, it will eventually reappear even if the crack is sealed.

Getting rid of potholes

Using a grinder, pits deeper than 1.5 cm must also be dug down to 2 cm. Next, use a hammer drill to remove the concrete from the pothole and clear the dust. "Epoxy" is applied to the crack at the following stage.

Once the surface has dried, level and fill the hole with repair mortar.

It is simpler to apply a thin layer of self-leveling compound where there are an excessive number of potholes.

Floor screed cracks frequently happen during the drying process as a result of poor mixing, quick drying, or inadequate curing. Uneven surfaces and possible structural problems may result from these fissures. It’s crucial to use the proper mix proportions, regulate the drying environment, and make sure the curing time is long enough to avoid this. If cracks do occur, they can typically be fixed by reapplying the screed in the troublesome areas or using specialty fillers. These actions contribute to a smooth, long-lasting floor.

Repairing bulging areas

Sections of the concrete base known as "bulging areas" start to shift when a load is applied. To fix this kind of harm:

1. Remove the coating to a stable surface and check it for cracks.
2. Remove the delaminated concrete, clean the slab and cover it with a primer.
3. Fill the resulting cracks with a construction mixture and let it dry.

By injecting concrete, damaged areas can also be repaired. To carry out this:

1. Mark the "affected" areas.
2. Using a hammer drill, drill holes in them 7-10 mm wide and up to 25 mm deep.
3. Using a construction syringe filled with "epoxy" fill the holes (do not fill immediately to the brim).
4. Wait until the resin hardens and "go" through the holes again with a syringe.
5. Repeat the procedure until the "epoxy" level stops decreasing.
6. Wait a day, during which it is not recommended to walk on the surface.

It is preferable to reinforce the base after repair work is finished to prevent future floor screed cracking.

Strengthening the screed after repair

The concrete slab needs to be strengthened in order to stop cracking repeatedly (especially if diagnostics reveal that inferior cement was used in installation). To carry out this:

1. Drill holes in the surface 2 cm deep (to the soil base or reinforced concrete slab), at a distance of 25 cm on each side.
2. In the upper parts of the recesses, drill support bowls 3 cm deep and with a diameter not exceeding the diameter of the holes.
3. Clean and prime the resulting holes and insert an anchor into them, class A III and at least 120 mm in size.
4. Fill the holes with a solution that is characterized by low viscosity (for example, "Rizopox 3500" or "Rizopox 1605").
5. Fill the supporting part with a construction and repair mixture.

Reason	Solution
Improper mix proportions	Use the correct ratio of materials, especially water and cement
Rapid drying	Cover the screed with plastic sheeting to slow down the drying process
Temperature fluctuations	Maintain a consistent temperature and avoid extreme changes
Poor substrate preparation	Ensure the base is clean, level, and properly primed before applying the screed
Insufficient curing time	Allow the screed to cure properly before applying any loads or finishes
Too much water in the mix	Follow the recommended water-to-cement ratio to prevent excess shrinkage

While cracks in a drying floor screed can be annoying, the first step in fixing the issue is figuring out why they occur. Common causes include things like incorrect mix ratios, quick drying times, and inadequate curing. You can guarantee a smooth, long-lasting surface and stop cracks by taking care of these problems.

If you do see cracks, don’t freak out. There are workable answers out there. Smaller cracks are frequently fixable with sealants or fillers, but larger damage may necessitate a complete examination and possibly a new screed application. The important thing is to move quickly to stop additional harm.

The likelihood of cracks during the screeding process can be greatly decreased with careful planning and attention to detail. When mixing, applying, and curing the screed, adhere to recommended procedures. You can achieve a faultless floor that endures over time with the appropriate strategy.

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