The Most Common Defects in Concrete Structures and How to Identify Their Causes
Concrete is a strong and durable material, but in practice, it is certainly not true that it can withstand everything. Concrete and reinforced concrete structures are exposed over the long term to water, freezing temperatures, salts, carbonation, chemical stress, mechanical stress, and defects from the original construction.
This can result in cracks, voids, spalling of the concrete cover, rust stains, salt efflorescence, water seepage, or a degraded surface.
However, it is important not to focus solely on the visible consequence. A crack, efflorescence, or rust stain are clues. The actual cause is often hidden deeper within the structure, in its composition, in the environment, or in the way it is stressed.
When rehabilitating concrete structures, it is therefore not enough to simply ask, “What should we use to repair it?” The more appropriate questions are: Why did the failure occur? How deep does it extend? Is the reinforcement affected? And what environmental conditions will the structure be exposed to after the repair?
Quick Response
The most common defects in concrete structures are cracks, reinforcement corrosion, spalling of the concrete cover, voids, water leakage, salt efflorescence, surface degradation, freeze-thaw damage, chemical deterioration, and abrasion of industrial floors.
The most common causes are concrete carbonation, chlorides, moisture, freezing, improper design details, high mechanical loads, chemically aggressive environments, or errors made during the original construction.
A proper repair must be based on identifying the cause of the malfunction. Otherwise, the problem may only be temporarily masked and will recur over time.
Why It Is Important to Identify the Cause of Concrete Defects
In concrete structures, a visible defect is often only the final stage of the problem. A rust stain, chipped concrete, or a crack is not, in and of itself, the cause. These are signs that the structure is losing its original function or protection.
A typical example is a balcony or loggia. Concrete begins to flake off the underside of the structure. The surface is cleaned, patched with restoration mortar, and repainted. At first glance, the job is done. However, if water continues to seep into the structure through faulty waterproofing—such as a problem at the railing, a joint, or a compromised membrane—the problem will return.
Similarly, in reinforced concrete, it is not enough to simply cover reinforcing bars that are already corroded. It is necessary to determine why the corrosion occurred. The cause may be carbonation, chlorides, insufficient cover over the reinforcing bars, prolonged moisture, or a combination of several factors.
A proper diagnosis helps determine the extent of the damage, the cause of the failure, the risk of further deterioration, the appropriate repair method, the necessary remediation system, and the need to protect the structure in the future.
Without this information, the repair is more of a guess than a professional procedure.
Overview of the Most Common Defects in Concrete Structures
| Visible manifestation | Possible cause | What could this mean? |
|---|---|---|
| Cracks in Concrete | shrinkage, loading, settlement, temperature changes, corrosion of reinforcement | The defect may be superficial, but it may also be structurally significant |
| Rust Stains | corrosion of reinforcing bars or metal components | The rebar loses its protective concrete cover |
| Concrete Spalling | corrosion of reinforcing bars, frost, water, poor substrate | damage to the surface layer or deeper degradation |
| A hollow sound when tapped | layer delamination, loose concrete, corrosion | risk of further dropout |
| Wet Maps | Leaks, moisture penetration, waterproofing failure | The structure is constantly exposed to water |
| White blooms | salt migration, moisture | Water transports salts through the structure |
| Surface flaking | frost, abrasion, poor-quality concrete, chemicals | loss of cohesion in the surface layer |
| Water Leak | cracks, construction joints, leaks | the need to address waterproofing, sealing, or grouting |
| Floor Damage | tablecloth, chemicals, impact load | an unsuitable or insufficiently durable surface layer |
| Defects Around Joints | structural movement, poor sealant, leak | The need to address seals and expansion joints |
Cracks in Concrete
Cracks are among the most common signs of defects in concrete structures. However, not every crack indicates the same problem. Some cracks are superficial and occur, for example, during shrinkage. Others may signal structural stress, settlement of the structure, corrosion of the reinforcement, or a design flaw.
So the first question isn’t how to seal the crack. It’s important to find out why it formed and whether it’s still active.
Surface shrinkage cracks
Shrinkage cracks often form during the early stages of concrete or mortar curing. They may be caused by rapid drying, improper curing, high temperatures, drafts, or an incorrect water-to-cement ratio.
Typical characteristics: They are fine, tend to be shallow, often form a grid-like pattern, usually do not penetrate deeply into the structure, and may not have any structural significance.
However, even with surface cracks, it is necessary to take the environment into account. A fine crack in a dry indoor space is a different problem than a crack on a balcony, bridge, ramp, or tank, where it could allow water to penetrate.
Structural and Static Cracks
Structural cracks can result from overloading, settlement, deflection, temperature changes, structural movements, or errors in design and construction.
Warning signs: the crack is growing, extends across the entire cross-section, is wider than typical hairline cracks, reappears repeatedly in the same location, is accompanied by deflection or displacement of a part of the structure, or is located on a load-bearing element.
For active or structurally significant cracks, a professional assessment is recommended. Simply filling the cracks on the surface may not be sufficient.
Cracks caused by corrosion of the reinforcement
Cracks often appear along the reinforcing bars in reinforced concrete. They occur when the steel reinforcement corrodes, expands in volume, and exerts pressure on the surrounding concrete.
Typical symptoms: a crack runs along the line of the rebar; rust stains appear; the concrete cover flakes off; the concrete sounds hollow when tapped; and the rebar may eventually become exposed.
In this case, simply filling the crack is not enough. It is necessary to address the condition of the reinforcement, remove the deteriorated concrete, treat the steel, and restore the protective function of the concrete cover.
Corrosion of Reinforcement
Corrosion of reinforcing steel is one of the most serious defects in reinforced concrete structures. Under normal conditions, concrete protects the reinforcing steel with its alkaline environment. If this protection is compromised, the steel can begin to corrode.
This is most commonly caused by concrete carbonation, chlorides from de-icing salts, prolonged moisture exposure, water infiltration, insufficient reinforcement cover, or poor-quality or damaged concrete.
Corrosion is not just an aesthetic problem. Corroding reinforcing bars expand in volume, putting pressure on the concrete and causing cracks, spalling of the concrete cover, and weakening of the steel itself.
How to Identify Corrosion in Reinforcing Bars
Reinforcement corrosion usually manifests as rust spots on the concrete surface, longitudinal cracks following the path of the reinforcement, spalling of the concrete, a hollow sound when tapped, exposed rebar, or delamination of the concrete layers from the substrate.
If the reinforcement is visibly exposed or severely weakened, it is necessary to assess not only the surface repair but also the safety and load-bearing capacity of the structure.
Carbonation of Concrete
Carbonation is a natural process in which carbon dioxide from the air penetrates the concrete and reduces its alkalinity. As a result, the concrete gradually loses its ability to protect the steel reinforcement from corrosion.
Carbonation itself may not be immediately visible. The problem arises when the carbonation front reaches the reinforcement and moisture is present at the same time. This significantly increases the risk of corrosion.
What are the signs of carbonation?
Carbonation often manifests itself indirectly: through corrosion of the reinforcement, rust stains, cracks along the reinforcement, spalling of the concrete cover, or reduced resistance of the structure to other factors.
In older reinforced concrete structures, carbonation is a common cause of failure, especially when the cover thickness of the reinforcement is thin or the concrete is exposed to moisture over a long period of time.
Chlorides and road de-icing salts
Chlorides are a particular problem for structures in transportation environments. They enter the concrete, for example, from de-icing salts and from the operation of garages, parking structures, ramps, bridges, and roads.
Unlike some other types of damage, chlorides can cause corrosion of the reinforcing bars even in concrete that may not appear significantly damaged at first glance.
High-risk structures include bridges, ledges, parking garages, underground garages, ramps, road embankments, and transportation and industrial structures.
How to Identify Chloride Accumulation
The surface may show spalling, damp spots, rust stains, concrete spalling, cracks along the rebar, or localized damage in areas where water and dirt accumulate.
However, chloride exposure cannot be reliably assessed by visual inspection alone. For larger structures, it is advisable to conduct a survey and, based on the results, design a repair and protection system.
Spalling of the Concrete Surface Layer
Concrete spalling is a typical sign that the structure is no longer just superficially damaged. It is most often the result of reinforcement corrosion, freeze-thaw cycles, prolonged exposure to water, or an unstable subgrade.
The concrete cover is designed to protect the reinforcing bars from external influences. If it is lost, the reinforcing bars are exposed to water, air, salts, and other corrosive substances.
What Can Cause Concrete to Flake Off
The most common causes are corrosion of the reinforcement, insufficient cover over the reinforcement, carbonation, chlorides, freeze-thaw cycles, water infiltration, mechanical damage, poor adhesion of a previous repair, or a poorly prepared substrate.
If concrete is flaking off repeatedly or over large areas, a professional assessment is recommended. Simply filling in the missing material usually does not solve the problem.
Hollows and Separated Layers of Concrete
A hollow sound when tapped is a common indication that the concrete or repaired layer is not bonded to the substrate. This could be due to a void, delamination, or a detached layer.
Common causes include corrosion of the reinforcement, poor substrate preparation, insufficient adhesion of the repair layer, moisture in the substrate, freeze-thaw damage, an unsuitable material, or a technical error during application.
Hollow spots are a risk because they can spread further. A layer that just sounds hollow when tapped today may fall off later.
Moisture, Leaks, and Water Seepage
Water is one of the most common causes of problems in concrete structures. While it may not immediately destroy the concrete on its own, it enables or accelerates other degradation processes.
For example, it contributes to reinforcement corrosion, freeze-thaw damage, salt efflorescence, chemical degradation, surface layer defects, and the growth of algae, moss, and biological fouling.
How to Identify a Moisture Problem
Typical symptoms include wet patches, dark stains, salt efflorescence, peeling paint, swelling or degradation of layers, water seepage around joints, water seeping through cracks, or recurring problems after repairs.
When dealing with moisture, it is essential to identify the source. Rainwater on a balcony is addressed differently than rising damp in masonry, pressurized water in an underground structure, or seepage through a construction joint.
Salt efflorescence on concrete
White or grayish-white efflorescence on the surface of concrete is usually related to moisture movement within the structure. Water dissolves salts or minerals, transports them to the surface, and leaves a visible coating after it evaporates.
Mold growth in and of itself does not necessarily indicate a structural emergency, but it is a clear sign that moisture is migrating through the structure.
Possible causes include water seepage, capillary action, high moisture content in the substrate, inadequate waterproofing, joint defects, or an inappropriate structural design.
If the blooms recur, simply cleaning them isn’t enough. You need to address the source of the moisture.
Freeze-Thaw Damage to Concrete
Freeze-thaw damage occurs mainly where concrete absorbs water and then freezes and thaws repeatedly. When water freezes, it expands and gradually weakens the concrete’s structure.
Outdoor structures are particularly at risk: balconies, loggias, ledges, plinths, stairways, ramps, retaining walls, bridges, and parking areas.
How to Recognize Frost Damage
Typical symptoms include surface crumbling, delamination, flaking of the concrete, loss of strength in the surface layer, edge spalling, or a combination of these with moisture and efflorescence.
In cases of freeze damage, it is necessary not only to repair the surface but, above all, to prevent water from penetrating the structure.
Chemical Degradation of Concrete
Concrete can also be damaged by chemically aggressive environments. This applies in particular to industrial facilities, sewer systems, wastewater treatment plants, reservoirs, agricultural structures, and structures exposed to chemicals.
Chemical exposure can cause deterioration of the cement paste, loss of surface strength, spalling, changes in the material’s structure, damage to protective layers, or corrosion of the reinforcement.
In such an environment, standard repair mortar is often insufficient. It is necessary to choose a system with the appropriate chemical resistance.
Abrasion and Mechanical Damage to Concrete Floors
Mechanical wear is a common problem with industrial floors. The surface is subjected to stress from the movement of material-handling equipment, falling objects, vibrations, abrasion, chemicals, and operational contamination.
Typical signs include a dusty surface, ruts, localized potholes, chipped joint edges, loss of flatness, damage in high-load areas, or peeling paint or coatings.
When it comes to floors, it’s not enough to simply address the pothole or crack itself. It’s necessary to take into account the type of traffic, load, chemicals, abrasion, substrate moisture, and the required downtime.
Defects in Joints, Expansion Joints, and Working Connections
Joints are critical points in concrete structures. It is precisely through these joints that water, dirt, salts, or chemicals often penetrate. At the same time, the joint must accommodate the structure’s movement.
Joint defects manifest themselves, for example, as torn or cracked sealant, leaks, water seepage, chipped edges, water infiltration, debris in the joint, or damage to the surrounding concrete.
The cause may be an improperly selected sealant, inappropriate joint geometry, a missing backing cord, movement of the structure, poor substrate preparation, or chemical exposure. For these defects, it is advisable to address not only the sealant but the entire joint detail.
Errors in the Initial Construction of the Concrete Structure
Some defects arise during construction but do not become apparent until years later. In such cases, repairs are more complicated because the issue is not merely the age of the material, but a structural or technological weakness.
Common errors include insufficient reinforcement cover, poor concrete compaction, a high water-cement ratio, an inappropriate mix design, improper curing of fresh concrete, poor-quality construction joints, inadequate drainage details, missing or inadequate waterproofing, improper connections to other structures, or the use of materials that do not meet technical specifications.
Such defects cannot be permanently resolved through localized repairs alone. The remediation plan must take into account why the structure is failing.
When Is a Problem Merely Aesthetic, and When Is It Technical?
Not every defect in concrete indicates a serious technical problem. Some issues may be primarily aesthetic. Others, however, point to a more serious problem with the structure, reinforcement, waterproofing, or surface protection.
More of a cosmetic flaw
An aesthetic or minor defect may include, for example, small surface pores, hairline shrinkage cracks without seepage, localized color variations, minor surface abrasions, or slight irregularities without signs of moisture or corrosion.
Here, too, it depends on the environment. In a dry indoor setting, a minor surface defect may be of little consequence. On an outdoor structure, balcony, garage, or tank, however, the same defect could allow water to penetrate.
Technical Malfunction
A technical defect is likely present if there are rust spots, a hollow sound when tapped, spalling concrete, exposed reinforcement, recurring water leakage, cracks that are widening, moisture-related salt efflorescence, damage to a load-bearing element, or a defect that has recurred after a previous repair.
When it comes to technical malfunctions, it is no longer enough to simply assess the appearance. It is necessary to determine the cause and, based on that, propose an appropriate repair procedure.
How to Distinguish Between the Symptoms and the Cause of a Disorder
When it comes to concrete, it is important to distinguish between what we see and what caused the defect.
| We can see on the surface | It’s probably happening inside |
|---|---|
| Rusty Spot | the rebar is corroding or is close to the surface |
| A crack along the rebar | Corrosion of the rebar puts pressure on the concrete |
| White bloom | Moisture migrates through the structure |
| Crumbling surface | frost, abrasion, chemicals, or poor-quality concrete |
| A hollow sound | The layer is separated from the substrate |
| Recurring Leaks | Failure of the waterproofing, joints, or details |
| Cancelled Repair | poor foundation, unsuitable material, or an unresolved cause |
If you mistake a symptom for the cause, the fix will only be temporary.
What to Do If a Defect Is Found in a Concrete Structure
When a problem is first detected, it is not necessary to know the final remediation plan right away. The important thing is not to skip the basic steps.
1. Assess the extent of the damage
First, you need to determine whether the issue is limited to a single location or whether the defect recurs in multiple parts of the structure. Pay particular attention to the number of defects, their size, location, whether the pattern repeats, their relationship to water, joints, edges, or reinforcement, and whether the condition is worsening.
2. Check the substrate’s adhesion
A hollow sound, peeling layers, or crumbling concrete indicate that the substrate is not in good condition. Applying a new layer to a non-cohesive substrate will not last long.
3. Assess the moisture level and the source of water
If the structure is damp, it is necessary to determine why. Otherwise, the repairs may have to be repeated over and over again. Water can enter from above through the building envelope, from the sides through joints, from the subgrade, through cracks, through construction joints, due to condensation, or through damaged waterproofing.
4. Check the condition of the reinforcement
With reinforced concrete, it is essential to know whether the reinforcement is corroded. If so, the repair must include cleaning, protecting, and restoring the protective layer.
5. Evaluate the structural environment
Different systems are designed for dry interiors, balconies, bridges, underground structures, water reservoirs, wastewater treatment plants, or industrial floors. The main determining factors are the presence of water, frost, salts, chemicals, mechanical loads, hygiene requirements, contact with drinking water or food, and downtime.
When Is It Necessary to Consult an Expert?
An expert assessment is recommended whenever a defect could affect the function, service life, or safety of a structure.
Be sure not to delay repairs if you notice exposed or severely corroded rebar, concrete spalling over large areas, cracks that are widening, recurring leaks, defects in the load-bearing structure, damage to balconies, loggias, or cornices, defects in bridges, garages, ramps, or parking structures; leaks in tanks and reservoirs; a chemically contaminated environment; or the failure of a previous repair.
In these cases, it is not a good idea to choose a material based solely on the product name. It is necessary to design the entire remediation system.
What types of materials are used to address concrete defects?
The choice of material always depends on the cause of the damage, the condition of the substrate, and the structure’s environment. In practice, a combination of several material groups is often used. The specific material system is selected based on the specific needs: restoring the shape, protecting the reinforcement, bonding to the substrate, waterproofing, sealing, grouting, chemical resistance, or final surface protection.
Repair mortars for concrete restoration
Repair and reprofiling mortars are used to fill in missing sections of concrete, restore shape, apply a covering layer, and repair localized defects. Depending on the specific application, the BETOSAN product line includes, for example, repair and reprofiling materials from the MONOCRETE, UNISAN, or DENSOCRETE series.
Corrosion protection for reinforcing bars, corrosion inhibitors, and bonding agents
For structures with damaged or corrosion-prone reinforcement, it is necessary to address the protection of the cleaned steel and the bonding of the new repair layer to the original concrete. In the BETOSAN product line, products such as DENSOCRETE 111 (corrosion protection / bonding agent), DENSOCRETE 222 (bonding agent), DENSOCRETE 333 (corrosion protection / bonding agent), UNISAN ADH 2K (corrosion protection / bonding agent with added corrosion inhibitors), ARMOGUARD N (corrosion inhibitor in coating form), or ARMOGUARD P (corrosion inhibitor as an additive). The specific choice depends on the condition of the reinforcement, the quality of the substrate, the type of repair, and the restoration technology.
Fine trowels and finishing coats
Fine trowels are used to level, seal, and finish the surface. These can follow a reprofiling repair and prepare the surface for a protective coating or other surface treatment. Depending on the type of substrate and the desired result, the BETOSAN product line includes materials such as the DENSOFIX, DENSOCRETE 555, or UNISAN SF 2K series.
Waterproofing Materials
If water is the cause of the problem, the solution must include waterproofing, sealing, or grouting. Without these measures, the problem may reoccur after repairs. BETOSAN offers systems such as WATERFIN, WATERFIX, WODAFLEX, and ELASTOFIN, as well as materials featuring XYPEX technology, for this purpose. The choice depends on whether the application involves surface waterproofing, a leak, a construction joint, a tank, a foundation, a balcony, or another type of structure.
Sealants, Gaskets, and Injections
Sealing and grouting materials are used for cracks, construction joints, expansion joints, or leaks. Products for caulking, sealing, and grouting can be used, including systems based on polyurethane or epoxy resins, depending on the type of defect.
Protective Coatings and Surface Systems
For structures exposed to carbonation, water, salts, chemicals, or the elements, final surface protection is essential. It helps limit further degradation and extend the service life of the repaired structure. The BETOSAN product line offers materials such as FLEXICOAT, BETOKRYL W, BETOSIL W, DENSOCURE R, and DENSOCURE W, which can be used in this area depending on the required function.
Why It’s Not Enough to Just Choose “Any Concrete Mortar”
A common mistake is to view a concrete defect as a hole that needs to be filled with something. However, with concrete structures, the entire system is often addressed: substrate preparation, reinforcement treatment (if necessary), an adhesive layer, reshaping repairs, a final skim coat, a protective coating, waterproofing, joint sealing, and, if necessary, grouting or reinforcement.
Even the best restoration material won’t help if the substrate is unstable, the structure continues to leak, the reinforcement remains untreated, or the chosen system is not suitable for the environment.
BETOSAN as a technical partner in addressing problems with concrete structures
BETOSAN s.r.o. is a Czech manufacturer of construction chemicals that has been in business since 1992. Its product range includes materials for reinforced concrete restoration, waterproofing, damp masonry restoration, industrial flooring, specialty mortars, synthetic resins, grouting, sealing, injection, and structural reinforcement systems.
When it comes to defects in concrete structures, it is not only the availability of a specific product that matters, but above all the right choice of system. In the field of restoration, there is no single universal solution that works for all structures. A balcony with damaged waterproofing requires a different approach than a bridge exposed to chlorides, a water tank, an industrial floor, or a routine local repair of reinforced concrete.
That is precisely why it makes sense to address more complex issues with technical support, which can help assess the condition of the structure, the environment, and the appropriate material solutions.
Availability of Remediation Materials in the Czech Republic
In restoration work, the true extent of the damage often becomes apparent only after the structure has been exposed. That is why the rapid availability of materials is also important. BETOSAN supplies materials from its own distribution centers in Prague, Batelov near Jihlava, Brno, Olomouc, Plzeň, Krnov, Chabařovice, and Ostrava. Upon agreement, materials can also be delivered directly to the construction site, which is particularly practical for larger restoration projects, industrial facilities, transportation infrastructure, or time-sensitive repairs.
Summary: Concrete damage is a warning sign, not just a surface defect
Cracks, rust stains, spalling concrete, voids, salt efflorescence, or water seepage are not just aesthetic problems. They are signs that the structure is exposed to factors that can further shorten its service life.
For minor and clearly defined defects, a localized repair may be sufficient. However, if the defect recurs, affects the reinforcement, is related to moisture, water infiltration, chemical exposure, or the load-bearing function of the structure, a professional assessment is required.
When dealing with concrete defects, it is therefore most important to distinguish between the visible symptoms and the actual cause. Only then does it make sense to select the appropriate material, repair method, and long-term protection for the structure.
Do you need to determine the cause of a defect in a concrete structure?
Are you dealing with cracks, concrete spalling, rebar corrosion, water leakage, or concrete floor damage? Contact BETOSAN technical support. We’ll help you choose the right material system based on the type of structure, the extent of the damage, and the environment to which the concrete will be exposed.
Frequently Asked Questions About Concrete Structure Failures
What are the most common defects in concrete structures?
The most common defects include cracks, corrosion of the reinforcement, spalling of the concrete cover, voids, surface crumbling, water seepage, salt efflorescence, freeze-thaw damage, chemical degradation, and abrasion of industrial floors.
How can you tell if a concrete structure needs a professional assessment?
A professional assessment is recommended in cases of exposed or corroded reinforcing bars, concrete spalling over large areas, widening cracks, repeated water infiltration, hollow spots, defects in load-bearing structures, or failure of a previous repair.
What causes rust stains on concrete?
Rust stains usually indicate corrosion of the steel reinforcement or metal components in the structure. In reinforced concrete, this is a warning sign, because corrosion of the reinforcement can lead to cracks and spalling of the concrete cover.
Why does concrete fall away from the rebar?
The most common cause is corrosion of the reinforcing bars. Corroding steel expands, putting pressure on the surrounding concrete, which then cracks or spalls off. This can be caused by carbonation, chlorides, moisture, or insufficient concrete cover.
What do white efflorescences on concrete mean?
White efflorescence usually indicates that moisture is migrating through the structure, carrying salts or minerals to the surface. If the efflorescence recurs, it is necessary to address the source of the moisture, not just clean the surface.
Are all cracks in concrete dangerous?
No. Some fine surface cracks may simply be shrinkage cracks. The cracks that pose the greatest risk are those that are growing, penetrate the structure, follow the reinforcement, are accompanied by water leakage, or appear on load-bearing parts of the structure.
Can concrete be damaged even if there are no visible cracks?
Yes. Some defects may initially manifest only as a hollow sound when tapped, increased moisture, salt efflorescence, rust stains, or degradation of the surface layer. In reinforced concrete, the problem may also be hidden within the reinforcement; therefore, a professional assessment is recommended for recurring or more extensive defects.
Why does concrete repair fail again over time?
Most often, this is because the actual cause of the problem has not been addressed. If the structure continues to leak, the reinforcement corrodes, the substrate is unstable, or an unsuitable material was chosen, the new repair will not last in the long run.
What material should be used to repair damaged concrete?
The material is selected based on the cause of the defect, the condition of the substrate, the extent of the damage, and the environment. This may include repair mortar, anti-corrosion protection for reinforcement, an adhesive bridge, a fine skim coat, a waterproofing system, grouting, joint sealing, or a protective coating.