How to waterproof concrete: a comprehensive guide to protecting structures from water

Water is one of the main factors contributing to the deterioration of concrete structures. Although this material is often considered extremely strong and durable, its natural porosity allows moisture to penetrate the cement matrix, especially when cracks, improperly sealed joints, or suboptimal construction details are present.

Water infiltration does not merely cause aesthetic problems such as moisture stains or salt efflorescence. Over time, it can compromise the durability of the entire structure, leading to corrosion of the steel reinforcement, loss of concrete cover, increased cracking, and a progressive decline in the concrete’s mechanical performance.

For this reason , waterproofing must be considered an integral part of the design and construction of any structure, whether civil or industrial. Taking preventive action reduces the risk of future water infiltration, minimizes maintenance requirements, and significantly extends the structure’s service life.

Today, there are numerous technologies available for waterproofing concrete. Choosing the most suitable solution depends on several factors: the type of structure, the stage of the project (new construction or an existing building), the presence of pressurized water, environmental conditions, and the characteristics of the construction details. Before delving into techniques and products, it may be helpful to understand why waterproofing has become an increasingly important element in the design and maintenance of civil engineering projects. We addressed this topic in the article dedicated to the importance of waterproofing structures in the era of climate change.

In this guide, we’ll analyze the main waterproofing techniques, the most common mistakes to avoid, and the solutions that enable the construction of safer, more reliable, and longer-lasting structures.

One of the most widespread beliefs is that concrete is naturally waterproof. In reality, this is not the case.

During the curing process of concrete, a network of capillary pores develops that can allow water and aggressive substances present in the environment to pass through. Even when the concrete is poured correctly, the material retains a certain degree of permeability, which can increase due to design errors, poor workmanship, or the normal aging of the structure.

Water is the primary vehicle through which external agents reach the interior of the concrete. Once it has penetrated, it can contribute to numerous forms of deterioration, some of which only become apparent after many years.

Among the main effects are:

• corrosion of metal reinforcement;
• carbonation of concrete;
• formation of salt efflorescence;
• deterioration caused by freeze-thaw cycles;
• detachment of the concrete cover;
• mold growth in underground areas;
• reduced durability of the structure.

Properly waterproofing concrete therefore means preserving its properties over time, reducing maintenance requirements, and increasing the structure’s safety.

This applies to both new construction and existing buildings, where timely intervention can prevent much more significant and costly damage.

To choose the most effective waterproofing system, it is essential to understand how water ingress into concrete occurs.
In most cases, water does not pass through concrete uniformly, but exploits specific points in the structure that offer less resistance to penetration.

One of the most important factors is the material’s natural porosity. If the water-to-cement ratio has not been correctly calculated or if vibration during casting was insufficient, the network of pores can become more extensive and facilitate the passage of moisture.

Cracks also constitute one of the main routes of water ingress. They can be caused by concrete shrinkage, structural movements, ground settlement or temperature fluctuations.

A key role is also played by what are known as construction details.

Statistics show that many leaks originate at:

• construction joints;
• concrete joints;
• pipe penetrations;
• connections between precast elements;
• manholes;
• drains;
• fixing points.

These are seemingly minor elements, but they are extremely sensitive, as they interrupt the continuity of the concrete and can become points of water ingress if not properly designed and protected.

Finally, hydrostatic pressure must be taken into account.

Foundations, retaining walls, underground car parks, tunnels and hydraulic structures are constantly subjected to the pressure of water present in the ground. Under these conditions, even a minor imperfection can lead to persistent water ingress that is difficult to eliminate.

Understanding the source of the problem is always the first step in choosing the most suitable waterproofing system.

There is no single system that works for all applications.

A concrete tank, a retaining wall, an underground parking garage, or a precast element each present completely different challenges and require solutions tailored to their specific operating conditions.

To identify the most effective method, several factors must be evaluated:

• whether the structure is new or existing;
• Is the water acting under pressure or through simple absorption?
• Are there cracks?
• Are there joints or construction joints?
• What are the environmental conditions?
• What will be the intended use of the structure?

Based on these assessments, three main intervention strategies can be identified:

• prevention during construction;
• waterproofing of existing structures;
• protection of construction details and joints.

Each of these requires different products and techniques, which we will analyze in the following sections.

Waterproofing a concrete structure does not simply mean applying a product to the surface. Every structure has different construction characteristics, environmental conditions and levels of exposure to water, which require specific solutions.
Choosing the correct system must therefore begin with an analysis of the problem: preventing water ingress in a new build is very different from working on a structure that has already deteriorated or from sealing a particularly critical area such as a construction joint.

The main waterproofing techniques can be divided into four categories:

1. waterproofing of concrete during the mixing stage;
2. waterproofing of existing surfaces and structures;
3. protection of joints and points of discontinuity;
4. protective and restorative surface treatments.

Each of these solutions serves a different purpose and, in many cases, can be combined with the others to achieve a comprehensive protection system.

Effective waterproofing depends not only on the choice of product, but above all on the correct planning of the work.

Among the most common mistakes are:

• carrying out work without having identified the actual source of the leak;
• neglecting joints and construction joints;
• using surface-level products for problems caused by pressurised water;
• applying coatings to degraded or inadequately prepared substrates;
• underestimating the importance of long-term maintenance of the structure.

Every project should be preceded by a careful analysis of the structure, its operating conditions and the ways in which water comes into contact with it.

Waterproofing concrete means ensuring the durability of the structure. There is no one-size-fits-all solution: the choice depends on the type of structure, the stage at which the work is carried out, and the conditions of exposure to water.

Proind’s solutions cover the entire life cycle of the structure, from protecting the concrete during the mixing stage with HYDROMAS and SIRIO SILICAFUME, to waterproofing coatings with SIRIOSEAL, right through to joint sealing systems, stopping active water ingress and providing surface protection for the structures.

Careful design, the use of specific products and professional installation are the best combination for creating durable, safe structures that maintain their performance over time.

Every waterproofing project requires a specific solution. The choice of product depends on the type of structure, the stage of construction and the problem to be solved. The table below summarises the main applications of Proind waterproofing systems.