Practically all engineering structures, regardless of their construction technology or design, require waterproofing or moisture protection. This is not only to prevent water from penetrating the interior of buildings but also to protect reinforced concrete structures from aggressive environments that could lead to the corrosion of concrete and reinforcement.

Traditionally, many structures have been sealed using the so-called "white tank" method, where the construction concrete itself serves as the waterproofing material. However, this approach has significant limitations and drawbacks that can render it ineffective, yet these issues are often overlooked in everyday discussions. This text will explain these limitations and drawbacks and demonstrate how to achieve a watertight structure using Hydrostop waterproofing technology in a "white tank" configuration.

2. "White Tank" – Risks

2.1. How Have Engineers Understood the Concept of a "White Tank" So Far?

The term "white tank" has transitioned from construction jargon into common usage within the building industry, referring to a method of creating seamless waterproofing. There is no universally agreed-upon definition for this type of waterproofing. On the construction market, "white tank" solutions are typically developed individually by companies specializing in such works.

A "white tank" refers to a monolithic reinforced concrete structure made using watertight concrete of at least class W8. For practical purposes, the structure is divided into sections, or "pours," to control the formation of cracks in predetermined locations. The design also specifies the maximum permissible width of cracks in the concrete, which is usually 0.2 mm, based on applicable standards. These standards are subject to ongoing updates to align with technological and material advancements, such as PN-EN 1992-3-2008 and the revised PN-EN 206:2014-04 standard from 2014.

A proper "white tank" waterproofing design should include the following:

• Identification of the minimum number of joints between structural elements,
• Methods to prevent shrinkage cracks,
• Optimization of the concrete mix design, including placement, compaction, and finishing techniques,
• Specification of reinforcement type and layout,
• Preparation of a concrete pouring schedule,
• Definition of expansion joints,
• Specification of controlled crack zones,
• Waterproofing solutions for construction joints.

In summary, designing a "white tank" requires strict adherence to high technical standards. Any deviations from the design specifications can compromise the watertightness of the structure.

This brings us to the core of the issue: while everything may appear flawless on paper—additional reinforcement is added, the structure is divided into sections, the concrete mix is poured under ideal temperature and humidity conditions, and curing is properly managed—the reality on construction sites often deviates from these ideal scenarios. From changing weather conditions to human errors, numerous factors can prevent the successful implementation of a "white tank."

2.2. Risks in the So-Called "White Tank"

2.2.1. Classification of Risks

The risks associated with a "white tank" can be divided into those occurring during the design phase and those during construction. Naturally, there are significantly more risks—and with a higher likelihood of occurrence—during the execution phase due to numerous factors beyond our control that can influence the quality of concrete works.

I. Design Phase

• Lack of soil investigations
• Incorrect building foundation design
• Failure to account for aggressive environmental conditions in the soil
• Designing concrete to allow for cracks up to 0.3 mm
• Incorrectly designed reinforcement (e.g., lack of anti-crack reinforcement for corners)
• Improperly selected concrete class and type

II. Construction Phase

A) Concrete Plant

• Incorrect concrete mix design
• Improperly selected aggregate
• Incorrect water-to-cement ratio
• Errors in using concrete admixtures
• Mistakes in dispatching the correct mix to the construction site

B) Transporting Concrete

• Excessive transport time to the construction site
• Adding water to the concrete mix by the truck operator

C) Installation of Waterstop Tapes in Construction Joints

• Absence of waterstop tapes in joints
• Incorrect installation of waterstop tapes
• Inappropriate selection of tape types
• Lack of continuity at tape connections
• Mechanical damage to tapes during concrete pouring
• Tapes not cleaned before subsequent concrete layers are poured

D) Placing Concrete Mix

• Dropping the concrete mix from excessive heights
• Equipment failure during concrete compaction (vibration)
• Inadequate or incorrect type of vibration equipment
• Interruptions in concrete delivery (excessive technological pauses)

E) Concrete Curing

• Insufficient curing time while in formwork
• Inadequate ambient humidity during curing
• Excessively low or high temperatures during curing
• Premature loading of the concrete with subsequent construction stages
• Malfunction of heating equipment (when pouring concrete in winter)

It may be argued that this is overly pessimistic and that such situations rarely occur in practice. However, the probability of these risks materializing is real. It is important to recognize that if even one of the listed issues arises, the structure may lose its watertightness and resistance to aggressive environments.

A particularly high risk of errors arises during the pouring and curing of the concrete mix. Many variables are outside our control, such as weather conditions, and others depend on the skills and diligence of on-site workers, who may perceive concrete curing as an unnecessary task.

The following photos, taken by our staff at construction sites across the country, confirm that such errors do occur.

Photo 1 illustrates discontinuities in waterstop tapes installed in a construction joint between the base slab and foundation walls. This lack of continuity is just the beginning of the issues. The tape on the left side of the image was improperly attached to the upper slab reinforcement, causing it to be pushed upward during concrete vibration. As a result, it is not embedded deeply enough in the concrete cover of the base slab and will not perform effectively along its entire length. Meanwhile, the tape on the right was embedded too deeply in the concrete (likely because the reinforcement was positioned too low, resulting in an overly thick concrete cover). Moreover, the protective film was not removed, meaning the tape was embedded along with the film. Consequently, it also cannot adequately seal the construction joint.

Fig. 1. Construction Errors: Incorrect Installation and Connection of Waterstop Tapes

In Photo 2, significant cracking can be observed in the reinforced concrete walls of reservoirs that were originally designed as a "white tank" system. The reservoirs were poured in two stages: initially up to half their height and subsequently the remainder. Unfortunately, the second stage was poured too quickly, before the lower section of the structure had achieved the required strength. The results are evident in the photo—severe and uncontrolled cracking occurred in the lower part of the structure.

Fig. 2. Construction Errors: Cracked Walls of Reinforced Concrete Reservoirs

These are, of course, extreme examples that are not commonplace on construction sites. However, the fact that such issues occur at all suggests that smaller errors are likely to happen as well. Even the smallest mistake during the execution of a so-called "white tank" can result in a lack of watertightness in the structure.

2.2.2. Carbonation of Concrete

In addition to errors that may occur at various stages of reinforced concrete construction, it is essential to consider the risks often overlooked by companies specializing in non-coating waterproofing solutions, which nonetheless do exist.

In descriptions of the "white tank" method found on the websites of such companies, statements like "A white tank is a structure with enhanced resistance to water penetration" or "Implementing a structure in the white tank system provides a high degree of safety in terms of water tightness" are frequently made. These claims focus on the watertightness of the structure—but what about protecting concrete against aggressive environments?

If such an environment reaches the concrete, carbonation will begin—a process in which carbon dioxide (CO2) reacts with calcium hydroxide (Ca(OH)₂) present in the concrete. This reaction produces calcium carbonate (CaCO₃), a mild acid that lowers the pH of the concrete, along with water (H₂O). Carbonation can reduce the pH of concrete from approximately 12.5 in fresh concrete to as low as 8.3. This pH reduction causes the concrete to lose its protective properties, leading to corrosion of the concrete itself and, subsequently, the reinforcement steel.

It is also worth noting that the CO2 responsible for this reaction is found in atmospheric air and rainwater. Therefore, all reinforced concrete structures must not only "ensure watertightness" but also be adequately protected against carbonation.

2.2.3. Concrete Resistance to Chemically Aggressive Environments

We already know that even rainwater can cause carbonation of concrete. However, in groundwater and liquids that come into contact with concrete—such as in wastewater treatment plants or swimming pools—environments with much higher levels of chemical aggressiveness are present. The degree of aggressiveness is defined according to PN-EN 206-1:2003, classifying environments as slightly, moderately, or highly aggressive. The same standard also provides the appropriate concrete strength classes, water-to-cement ratios (W/C), and minimum cement content in the mix to ensure resistance to specific aggressive environments.

Table 1. Recommended Limit Values for Concrete Composition and Properties According to PN-EN 206-1:2003

It is important to consider how these values are monitored. A sample of concrete mix, collected either at the batching plant or directly from the mixer truck on-site, is poured into a 15x15 cm mold, properly compacted (often using a vibrating table), and carefully cured to provide ideal conditions for concrete setting. The sample is then tested in a construction laboratory to ensure proper bonding and the absence of shrinkage cracks.

Unfortunately, in field conditions at construction sites, concrete rarely experiences such ideal curing conditions. In summer, temperatures may be too high; in winter, there is a risk of freezing, or it may rain, or prolonged dry spells may occur—all of which significantly affect the final outcome. If concrete is not adequately cured, shrinkage cracks will form. Once these cracks appear, the aggressive environment will penetrate the concrete and reach the reinforcement. In this way, the resistance of concrete to aggressive environments often remains purely theoretical.

3. Hydrostop Waterproofing in White Tank Technology

3.1. About Hydrostop

Waterproofing solutions branded as HYDROSTOP® were introduced to the Polish market over 30 years ago. Hydrostop materials share a key feature: the ability for osmotic and capillary penetration of sealing components into concrete, mortar, and masonry materials. Upon contact with moisture and cement, the sealing components induce additional crystallization, sealing micro-cracks and capillaries within the structure. The crystallization process gradually stops as defects are resolved and moisture is depleted (Fig. 3). However, if water re-enters the concrete structure over time (e.g., due to the formation of shrinkage cracks), the crystallization process reactivates, and the crack is gradually sealed by the deposition of insoluble salt crystals. This self-sealing mechanism ensures the concrete remains watertight (Fig. 4).

Fig. 3. Diagram of Concrete Sealing with Hydrostop Materials: 1. Water pressure, 2. Application of the product, 3. Penetration/crystallization within the concrete structure, 4. Sealed concrete.

Fig. 4. Sealing a Crack through Crystallization of Hydrostop Sealing Components
The crystallizing properties have been tested and confirmed by the Building Research Institute in Warsaw

Fig. 5. ITB Report on Hydrostop Materials Testing

3.2. How Hydrostop Technology Mitigates Risks Associated with Constructing a "White Tank"

The main risks identified in the second section regarding "white tank" construction are carbonation and resistance to aggressive environments. Mitigating these risks largely depends on the quality of the contractors' work, atmospheric conditions, and other factors we may or may not be able to control. Below, we explain how Hydrostop technology, through its osmotic and capillary penetration properties and its ability to induce additional crystallization in concrete, helps eliminate most of these risks.

3.2.1. Carbonation

Carbonation is a chemical reaction where carbon dioxide (CO₂) reacts with calcium hydroxide (Ca(OH)₂) in the concrete. This reaction forms calcium carbonate (CaCO₃), which reduces the concrete's pH and generates water (H₂O). Carbonation can lower the pH of concrete from approximately 12.6 for fresh concrete to as low as 8.3. The primary concern with this process is that such a pH drop significantly diminishes the concrete's protective properties, initiating corrosion in the concrete and reinforcing steel.

To strengthen concrete against this threat, products resistant to such environments are necessary. From Hydrostop's product range, the following are ideal:

• Professional Mixture 209 or Penetrating Mat 541 for vertical insulation (e.g., walls, interior of tanks),
• Mixture 203 for horizontal insulation.

All these products are resistant to pH levels ranging from 5.5 to 12.5, ensuring that carbonation risks are eliminated upon application.

Fig. 6. Hydrostop Products: Professional Mixture 209, Penetrating Mat 541

3.2.2. Aggressive Environments

Another significant risk is the presence of aggressive environmental conditions in the soil, which can deteriorate the structure of concrete. The solution to this risk involves the same Hydrostop products: for vertical insulation (walls, tank interiors), Professional Mixture 209 or Penetrating Mat 541, and for horizontal insulation, Mixture 203. These products are resistant to aggressive environments up to level XA2, including household and agricultural wastewater (e.g., slurry), chlorinated drinking water, and pool water (XD2), as well as fats, mineral and edible oils, transformer oils, sulfates, phenols, and lactic acid.

For highly aggressive XA3 environments, an additional chemically resistant layer is required, such as the Hydrostop Epoxy Impregnant 801+802. It is worth noting that XA3 environments are typically found only in chemical plants. All other commonly encountered risks fit within the XA2 level of aggressiveness.

3.2.3. Shrinkage Cracks

Shrinkage cracks can occur for numerous reasons, including poorly installed reinforcement, incorrect concrete mix, improper placement and compaction, lack of concrete curing, or excessive loading of the structure during subsequent construction stages. Regardless of the cause, the result is the same: aggressive environments and moisture penetrate the concrete structure, initiating corrosion.

How can this risk be mitigated? The solution is identical to the previous ones: for vertical insulation (walls, tank interiors), Professional Mixture 209 or Penetrating Mat 541, and for horizontal insulation, Mixture 203. All of these products have the ability to seal cracks up to 0.5mm wide, as confirmed by tests conducted by the Building Research Institute (Fig. 5 – ITB Report on Hydrostop materials).

3.2.4. How to Use Hydrostop Materials

Hydrostop materials are easy to apply and significantly save time on construction sites.

For heavy-duty insulation of foundation slabs with Mixture 203, apply a dry sprinkle using a sieve with 1.5–2mm mesh directly before concreting, through the reinforcement bars, onto the lean concrete. The concrete mix is then poured over this prepared layer. This method allows the insulation to be performed almost simultaneously with concreting, as two workers can cover up to 500m² of sprinkle layer in an hour.

Using dry sprinkle insulation on the bottom and top of the slab is approved under Technical Approval ITB AT-15-2680/2016 for Mixture 203 and AT-15-7076/2014 for Professional Mixture 209.

Fig. 7. Application of Hydrostop dry sprinkle on the underside of the foundation slab

Fig. 8. Application of Hydrostop dry sprinkle on the top surface of the foundation slab in a multi-level parking structure

The insulation of vertical reinforced concrete elements is applied using Professional Mixture 209 with a brush or a spray machine. The product can be applied to freshly stripped concrete, allowing for a shortened work schedule.
Fig. 9. Application of Hydrostop product on a freshly stripped side of the foundation slab.

3.3. Hydrostop-3 – A Method to Avoid Errors During Waterproofing Execution

Hydrostop-3 is a company within the Hydrostop Group that specializes in providing services for waterproofing new structures and sealing or repairing existing building constructions. With years of experience in waterproofing work, the company ensures high-quality services. Its offerings include:

• Designing and delivering comprehensive waterproofing solutions for underground building parts during construction.
• Sealing and repairing existing building structures.
• Reinforcing building constructions.
• Stabilizing and strengthening soils.
• Dewatering excavations.
• Drilling in concrete and creating watertight penetrations.

Thanks to its well-defined scope of operations, Hydrostop-3 provides highly professional services, employing specialists in waterproofing. By taking on even the most challenging projects, the company continually enhances its expertise and raises the standard of its services.

Fig. 10. Installation of sealing tape in a construction joint by Hydrostop-3 workers

As an example of an extremely challenging project, we can highlight the sealing of a base plug during the construction of the Museum of the Second World War in Gdańsk. When Hydrostop-3 workers arrived at the site, they encountered the situation depicted in Fig. 11. The diaphragm walls were completed, the soil was excavated, and the base plug was poured, but it was so severely cracked that pumps could not drain the excavation. The work on sealing the base plug began with the involvement of divers, who, in collaboration with our workers operating from a barge equipped with the necessary tools, performed initial sealing injections.

Fig. 11. Construction of the Museum of the Second World War – the start of Hydrostop-3's work

Only after the base plug was sufficiently sealed to allow pumps to remove the water did further waterproofing work commence. However, this was no simple task. The cracks that remained to be sealed had widths of up to 6 cm, making traditional methods ineffective. Nevertheless, thanks to Hydrostop-3's innovative approach to waterproofing, a successful method was developed.

Fig. 12. Construction of the Museum of the Second World War - final stage of sealing.

Initially, wooden planks wrapped in geotextile were driven into the cracks in the foundation plug to preliminarily limit water flow. Only then were the cracks gradually sealed using pressure injections with fast-expanding materials. The process was lengthy and labor-intensive but ultimately successful.

Hiring Hydrostop-3 to execute waterproofing using the Hydrostop white-tank technology helps avoid errors during the implementation phase. The Hydrostop-3 team focuses exclusively on waterproofing— they don't install windows or build walls, but instead specialize solely in sealing structures. This focused expertise enables them to gain increasing experience and avoid errors mentioned in section 2.2.1, such as poorly chosen water-stop tapes or improper tape connections.

4. Conclusions

Implementing waterproofing as the so-called "white tank," where the structural concrete itself serves as the waterproofing material, is a common practice on construction sites. However, this method requires contractors to adhere to strict guidelines regarding the selection of the concrete mix, the installation of additional reinforcement, and, most importantly, the curing of freshly poured concrete to prevent shrinkage cracks. This process is influenced by numerous factors, not all of which can be controlled (e.g., weather conditions). Any error in this complex procedure can compromise the structure's watertightness. Additionally, aggressive environmental factors, which are not limited to wastewater treatment plants but are present in air and rainwater, pose further risks to these structures.

It is worth noting that the PN-B-03264:2002 standard, on page 90, under Table 21, detailing the minimum concrete cover thickness for corrosion protection, includes the following statement: "In environments aggressively affecting concrete (classes XF and XA), particular attention should be paid to the structure of the concrete, and in the case of chemical aggression (XA) – to the need for surface protection of the concrete."

The solution lies in using Hydrostop waterproofing in white-tank technology. Thanks to Hydrostop's unique ability for osmotic and capillary penetration of its sealing compounds into the concrete, mortar, and masonry, its components react with moisture and cement to trigger additional crystallization. This process seals microcracks and capillaries in the concrete's structure. Crystallization gradually ceases as defects are repaired and moisture is exhausted. However, if water re-enters the concrete later (e.g., due to the formation of shrinkage cracks), the crystallization process reactivates, and the cracks are gradually sealed with insoluble crystalline salts, allowing the concrete to self-seal.

These properties of Hydrostop materials ensure that the structure is resistant to aggressive environments that cause corrosion. If errors occur in the curing process and shrinkage cracks form, these will self-seal through crystallization, as confirmed by testing conducted on Hydrostop products by the Building Research Institute. Additionally, by contracting Hydrostop-3 for comprehensive waterproofing services, errors related to sealing construction joints can be avoided, thanks to their extensive experience with challenging projects.

Hydrostop waterproofing in white-tank technology is the key to your success.

For more information about all available products and contact details for Hydrostop's regional advisors, please visit the website.

www.hydrostop.pl