Construction Chemicals: 10 Most Common Questions About Hydrophobic and Waterproofing Additives

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Hydrophobic and waterproofing additives are key components of modern construction chemistry. Their correct selection and application determine the resistance of structures to moisture, frost, and chemical influences. Nevertheless, manufacturers and processors often face similar questions: What is the difference between hydrophobisation and waterproofing? Why do some additives lose their effectiveness after a few years? Or how to prevent compatibility issues when combining them with other additives? In this article, we summarise the answers to ten of the most common questions our customers ask – from laboratories to large-scale producers of mortars and concretes.

1. What is the difference between hydrophobic and waterproofing additives?

Hydrophobic and waterproofing additives are often confused, but they serve different functions in construction materials. Hydrophobic additives, such as silicones or silanes, reduce the surface absorbency of the material by creating a water-repellent layer on its surface. Water then runs off or beads up without penetrating the structure. These additives are ideal for façade plasters, masonry, or concrete surfaces where the goal is to prevent dampness and subsequent damage from frost or salts. However, they do not prevent water seepage under pressure, such as during leaks or a pressurized water column.

Waterproofing additives, on the other hand, create an impermeable barrier that resists even water pressure. These typically consist of polymers, bitumen emulsions, or cement mixtures with special additives that completely block water penetration. They are used, for example, in underground structures, swimming pools, or tanks where absolute water tightness is required. While hydrophobic additives are suitable for surface protection, waterproofing additives provide deep protection for the structure.

2. How to correctly apply hydrophobic additives to façades?

Applying hydrophobic additives to façades requires careful surface preparation and adherence to technological procedures. First, it is necessary to remove all dirt, moss, algae, and old coatings that could hinder the penetration of the additive. The substrate must be dry, clean, and mechanically stable—a damp or powdery surface significantly reduces the effectiveness of hydrophobization. The ideal temperature for application ranges between 5 °C and 25 °C, and direct sunlight or rain should be avoided during drying.

The additive is applied using standard methods, such as brushing, rolling, or spraying, in one or two layers. It is important to adhere to the recommended amount – a layer that is too thin will not provide sufficient protection, while an excessive amount may lead to film formation or stains. After application, it is advisable to let the surface dry for 24 to 48 hours before the first contact with water. The effectiveness of the waterproofing can be verified with a simple test: a drop of water should bead up and not soak into the surface.

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3. What are the most common mistakes when selecting waterproofing additives?

Choosing the wrong waterproofing additive can lead to serious problems such as moisture penetration, mold, or structural damage to the building. One of the most common mistakes is underestimating the type and intensity of water exposure. For example, for underground walls exposed to a pressurized water column, an additive with high pressure resistance must be selected, while for interior damp spaces, a lighter solution is sufficient. Another mistake is ignoring the compatibility of the additive with the substrate – some polymers or bitumen emulsions may not adhere well to certain types of concrete or plaster.

Another issue is the failure to follow technological procedures, such as incorrect mixing, insufficient layer thickness, or application on an improperly prepared substrate. For instance, dust or grease residues can significantly reduce the adhesion of the waterproofing layer. It is also important to consider the chemical resistance of the additive – some aggressive environments, such as wastewater or industrial chemicals, require special types of waterproofing. It is always advisable to consult the selection with an expert and follow the manufacturer's technical data sheets.

4. How long does the effect of hydrophobic and waterproofing additives last?

The lifespan of hydrophobic and waterproofing additives depends on several factors, including the type of additive, substrate quality, environmental conditions, and exposure intensity. Silicone- or silane-based hydrophobic additives typically last 5 to 10 years, with their effectiveness gradually decreasing due to weather conditions, UV radiation, and mechanical wear. For façade applications, it is recommended to check effectiveness every 3 to 5 years and, if necessary, renew the hydrophobic layer. The test can be performed simply – if a water droplet stops beading and begins to absorb, it is time for renewal.

Waterproofing additives generally have a longer lifespan, often 10 to 20 years, but the quality of application and type of material also play a role. For example, polymer-modified cementitious waterproofing can be more durable than bituminous emulsions, which are more susceptible to UV degradation. In demanding conditions, such as underground structures or swimming pools, it is advisable to carry out regular leak checks and, if necessary, repair damaged areas. The key to long-term durability is proper maintenance and timely renewal of protective layers according to the manufacturer's recommendations.

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5. Can hydrophobic additives be combined with other construction chemicals?

Combining hydrophobic additives with other construction chemicals is a common practice but requires careful consideration of compatibility and effect. For example, when used with plaster mixes or mortars, it is crucial to verify whether the hydrophobic additive affects adhesion, strength, or setting time. Some silicone or silane hydrophobic additives may react with the alkaline environment of cement, leading to reduced effectiveness or undesirable chemical reactions. Therefore, it is advisable to perform a small-scale test application before combining them and monitor the resulting material properties.

Another aspect is the interaction with paints, coatings, or adhesives. Hydrophobic additives can reduce surface wettability, which may impair the adhesion of subsequently applied layers. In such cases, it is recommended to use special penetrating coatings or adhesion promoters to ensure compatibility between layers. It is always necessary to follow the manufacturers' technical data sheets and consult combinations with experts to avoid compromising the functionality of individual components.

6. How do waterproofing additives affect ecology and worker health?

Modern waterproofing additives are developed with ecological and health requirements in mind, but their use still requires adherence to safety measures. According to REACH and CLP regulations, all chemical substances must be properly labeled, and their safe use described in safety data sheets. Some waterproofing additives, particularly those based on solvents or reactive resins, may release volatile organic compounds (VOCs), which burden the environment and can irritate workers' respiratory tracts. Therefore, water-dilutable or low-VOC systems are increasingly being adopted.

To protect workers' health, it is essential to use personal protective equipment such as gloves, safety goggles, and respirators, especially when working with concentrated products or in enclosed spaces. It is also important to ensure adequate ventilation and minimize direct skin contact. The environmental impact can be reduced by choosing products with Ecolabel certification or those that meet low toxicity requirements for aquatic organisms. Local regulations and manufacturer recommendations should always be taken into account.

7. How to Test the Effectiveness of Hydrophobic and Waterproofing Additives Before Application?

Testing the effectiveness of hydrophobic and waterproofing additives before large-scale application is crucial to ensure the desired properties and long-term functionality. A basic test for hydrophobic additives is the wettability test, where a drop of water is applied to the treated surface and the wetting angle is observed. If the surface is properly hydrophobized, the drop remains spherical and does not absorb. For quantitative evaluation, standard test methods for measuring water repellency can be used, such as capillary suction or gravimetric determination of absorbency.

For waterproofing additives, it is important to verify resistance to water penetration under pressure. This is done through water tightness tests, where water pressure is applied to a material sample and it is observed whether any leakage occurs. Another criterion is tensile strength under bending or resistance to alkaline environments, which simulates conditions in concrete. Tests should be carried out in accordance with applicable standards and, ideally, in accredited laboratories to ensure reliable and reproducible results.

Do you have specific waterproofing requirements?

Every construction application requires an individual approach. GCG Group supplies a wide portfolio of hydrophobic and waterproofing additives, including detailed technical data sheets and safety data sheets (SDS). Our experts will help you select the optimal solution for your specific formulation and processing conditions. Contact us – or browse our catalog of over 1,300 products right away.