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March 20, 2026
Water ingress through concrete is one of the most persistent and destructive forces an engineer or contractor will encounter. Cracks, construction joints, and the natural porosity of concrete all create pathways for groundwater to enter tunnels, basements, foundations, dam galleries, and underground structures. When that water is under pressure, the problem becomes acute: surface-applied coatings fail, membranes delaminate, and conventional repair mortars wash out before they can cure.
Injection waterproofing is the category of techniques that addresses this challenge from the inside out. Rather than applying a barrier to the surface, injection methods introduce a sealing material directly into the crack, joint, or pore network under controlled pressure — displacing water and forming a permanent barrier within the structure itself.
This guide explains how injection waterproofing works, what materials are used, where it is applied, and how to select the right system for your project — including a detailed comparison of bentonite gel, polyurethane, and acrylate injection systems.
Injection waterproofing — also called pressure injection, crack injection, or structural injection — is a remediation technique in which a fluid or gel material is introduced into a concrete structure through pre-drilled holes, under controlled pressure, to seal cracks, joints, voids, or porous zones.
The principle is hydraulic displacement: the injected material travels along the same pathways as the water, pushes the water out, and solidifies or remains as a permanent flexible gel to prevent further ingress. The injection can be performed whether the structure is dry, damp, or under active water pressure — a critical advantage over surface-applied systems.
Surface waterproofing systems — sheet membranes, cementitious coatings, bitumen layers — create a barrier on the exterior or interior face of a structure. They rely on adhesion, which fails when there is moisture behind them or when the substrate moves. They also require access to the outer face of the structure, which is frequently impossible in existing infrastructure.
Injection waterproofing works from the accessible side. A contractor drills injection ports into the accessible face (almost always the interior), and the material travels inwards and outwards along crack planes and joint voids. No excavation is required. The seal is created within the body of the structure, making it structurally integrated rather than surface-dependent.
Key advantage: Injection waterproofing is the only technique that can permanently seal an active water leak — where water is flowing through the crack at the moment of repair — without excavation or surface preparation.
The choice of injection material determines the performance, longevity, and environmental profile of the repair. There are four principal categories in commercial use:
Bentonite is a naturally occurring aluminium phyllosilicate clay mineral, specifically sodium-activated montmorillonite. When formulated as an injection gel, it behaves as a thixotropic fluid: it becomes low-viscosity under the shear forces of injection pressure, allowing it to penetrate deep into crack networks, and then returns to a stable gel state once pressure is released.
The fundamental mechanism is water absorption and displacement. Bentonite has an exceptional affinity for water molecules: it absorbs water into its crystal lattice, swells, and forms an impermeable physical barrier. In the context of injection waterproofing, this means the gel actively extracts residual moisture from the crack or joint and incorporates it into its own structure, creating a permanent, self-sealing barrier at the capillary level.
The primary product in this category is Euras Gel Type-B, a one-component injection gel of mineral origin with a molecular particle size of approximately 1 nm — roughly 20 to 50 times smaller than polyurethane or acrylate particles. This nano-scale particle size allows penetration into microcracks as narrow as 0.1 mm, well below the threshold of conventional polymer injection systems.
Key properties: Operates at -50°C to +100°C. Non-toxic, non-flammable, solvent-free. Works in wet and dry conditions. No surface preparation required. Injection pressure 2–200 bar. Zero maintenance post-application. Tested service life: 30 years.
Polyurethane injection systems are the most widely used polymer-based alternative. They fall into two sub-categories: hydrophilic foams, which expand on contact with water, and hydrophobic resins, which repel water and cure independently of moisture.
PUR hydrophilic foams are effective for rapid emergency sealing of active leaks — the expansion reaction can stop water flow quickly. However, they have significant long-term limitations: the foam can contract when dry, leaving voids; the 3:1 expansion ratio can impose structural stress on crack faces; and polyurethane degrades over time, typically requiring re-injection within 10 to 15 years. PUR resins also contain isocyanate compounds, which are classified as hazardous and require specialist handling and disposal.
Limitation: Polyurethane systems require a minimum substrate temperature of +5°C and most perform poorly at moisture content above 2%. They cannot match the temperature range or longevity of mineral systems.
Acrylate gels offer very low viscosity, which gives them excellent penetration into fine microcracks and soil voids. They are widely used in ground stabilisation and fine-crack sealing. However, they are synthetic polymers with finite service lives, and their ultra-low viscosity can make control difficult in structures with large crack openings or high water flow rates.
Crystalline waterproofing products work through a chemical reaction with unhydrated cement particles in the concrete matrix, forming insoluble crystals that block pore pathways. They are effective for sealing hairline cracks in concrete with a good residual cement content, but they are limited to static cracks of less than 0.4 mm, require a 28-day activation period, and cannot seal active leaks or dynamic cracks.
The table below compares Euras Gel Type-B against the most common alternative injection technologies across the criteria that matter most to specifying engineers and project managers.
| Criteria | Euras Gel Type-B (bentonite) | Conventional methods |
|---|---|---|
| Surface preparation | None required — works on wet or dry | Dry surface mandatory for most systems |
| Works on active leaks | Yes — injected under live water flow | No — most systems fail if water present |
| Temperature range | -50°C to +100°C | +5°C to +35°C for most PUR systems |
| Injection pressure | 2–200 bar (adapts to site conditions) | Typically limited to 50–100 bar |
| Environmental status | Non-toxic, mineral, solvent-free | PUR contains isocyanates; acrylic VOCs |
| Maintenance after application | Zero — permanent seal | Periodic re-injection typically required |
| Crack width capacity | Up to 2.5 mm dynamic cracks | Crystalline: ≤0.4 mm static cracks only |
| Cure / set time | Near-instant; full settlement 2–4 hours | 24–72 hours for epoxy; PUR 10 sec–20 min |
| Service life tested to | 30 years | 10–20 years for membranes and PUR |
Specifier's note: For projects with active water ingress, high hydrostatic pressure, sub-zero temperatures, or restricted access, bentonite gel injection is the only system that addresses all constraints simultaneously without requiring dry conditions or surface preparation.
Injection waterproofing is applicable across the full range of concrete infrastructure. The following structure types account for the majority of injection projects globally:
Water ingress through segment joints, crown cracks, and annular voids is one of the primary maintenance challenges for urban transit tunnels. Injection is performed from inside the tunnel bore, eliminating the need for any ground-side access. At the Attiko Metro in Athens and across multiple projects on the Djerdap hydroelectric complex in Serbia, Euras Gel Type-B has been used to permanently seal joint leakage at pressures up to 50 bar.
Dam galleries, turbine rooms, and control structures are exposed to constant high-pressure groundwater. The Kissir Barrage in Algeria and the Ourkiss Barrage demonstrate typical applications: injection of bentonite gel into concrete segment joints, replacing degraded existing waterproofing layers and preventing future ingress. Over 500 kg of gel was used at the Melchsee-Frutt dam overflow structure in Switzerland, sealing cavities discovered within what appeared to be a sound concrete structure.
Approximately 78% of multi-level car parks develop water ingress within 10 years of construction due to thermal cycling and joint movement. Basement construction joints — the interface between the floor slab and the wall — are the most common failure point. Injection seals these joints from the interior face without excavation, typically in a single visit.
Foundation waterproofing by injection is particularly valuable for existing structures where access to the external face is impossible without disruptive excavation. Injection ports are drilled through the internal slab or wall, and gel is injected at calculated intervals to create a complete curtain seal.
Bentonite gel is certified safe for use in structures in contact with drinking water, making it one of the few injection materials appropriate for water treatment facilities. It seals both internal pressure (hydrostatic load from the contained water) and external groundwater pressure simultaneously.
Projects at the Felslabor Grimsel underground research laboratory in Switzerland, military bases in Germany and Serbia, and the US Army Kaserne in Hanau demonstrate the use of injection waterproofing in sensitive environments where environmental compliance and long-term reliability are paramount.
Before any drilling begins, the engineer maps the leak points, measures water flow rates and pressures, and assesses the concrete quality, crack geometry, and joint condition. This determines the injection port spacing, required gel volume, and appropriate injection pressure range.
Holes are drilled at a calculated angle and spacing to intercept the crack plane or joint at the appropriate depth. Typically, holes are drilled at 45° to the surface to intersect the crack at approximately mid-depth. Port spacing depends on crack width and water pressure but typically ranges from 200 mm to 500 mm.
Mechanical packers are installed into the drilled holes. Each packer has a one-way valve that allows material in at injection pressure but prevents backflow. The engineer designates each packer as either an operating packer (through which gel is injected) or a control packer (through which gel emergence is monitored to confirm penetration).
The gel is connected to the injection pump and introduced under controlled pressure, starting from the lowest point on vertical cracks or from one end on horizontal joints. Pressure is typically in the range of 2 to 200 bar, adjusted based on real-time resistance feedback. Injection continues at each operating packer until gel appears at the adjacent control packers — confirming that the crack or joint has been fully displaced.
Following injection, the treated areas are monitored over 24 to 48 hours to confirm cessation of seepage. If any point remains wet, targeted re-injection is performed. The packer holes are then grouted with non-shrink mortar.
The only materials suitable for actively flowing water are those that can displace water under pressure. Bentonite gel and PUR hydrophilic foams are the two options. For long-term performance, mineral bentonite gel is preferred: it does not degrade, does not contain isocyanates, and its nano-scale particle size provides deeper penetration into the void structure.
PUR and acrylate systems have minimum application temperatures of +5°C and typically degrade below -20°C in service. Bentonite gel operates continuously from -50°C to +100°C, making it the only suitable system for alpine infrastructure, cold-climate tunnels, and refrigerated structures.
Polyurethane injection products contain free isocyanates and cannot be specified near drinking water without specific certification. Bentonite gel is mineral, non-toxic, non-flammable, and carries no hazardous substance classification under GHS or EU regulations (1272/2008/EC). It is the appropriate choice for water treatment infrastructure, food processing facilities, and environmentally sensitive sites.
Cracks that continue to open and close due to thermal cycling, structural settlement, or vibration will break any rigid injection material. Bentonite gel remains permanently flexible and self-healing — if a crack opens slightly after treatment, the gel accommodates the movement and maintains the seal. Epoxy injections and crystalline systems are rigid and will fracture under dynamic movement.
For very fine cracks (below 0.3 mm) and densely compacted concrete, particle size determines penetration depth. At 1 nm molecular scale, bentonite gel accesses pathways that no polymer system can reach.
The environmental profile of injection materials is increasingly critical for public infrastructure procurement, BREEAM and LEED certified projects, and structures in contact with groundwater.
Polyurethane injection products are subject to VOC emission restrictions and require specialist waste disposal. Most PUR systems fail to meet LEED v5 VOC thresholds. Acrylate gels are water-soluble and carry risks of groundwater contamination at high injection volumes.
Bentonite gel injection offers a fundamentally different profile. Bentonite is a naturally occurring mineral with no synthetic chemistry. It carries no hazardous substance classification, emits no VOCs, and its CO₂ footprint per unit of protection is approximately 0.3 kg CO₂e/SF — compared to 1.2 kg CO₂e/SF for bituminous membrane systems. For projects required to meet ASHRAE 189.1 durability mandates or EPA TSCA Title 40 VOC restrictions, mineral injection gel is the compliant choice.
Euras Technology has been manufacturing and applying mineral bentonite injection gel since 1995. The Euras Gel Type-B formula represents 30 years of development in nano-scale mineral processing: single-layer montmorillonite delamination achieves particle sizes as low as 1 nm without chemical treatment — a capability that conventional bentonite processing cannot replicate.
Where conventional bentonite products from market leaders such as Sika require geotextile systems and are limited to pre-construction applications, Euras Gel Type-B is a post-construction remediation product that can be injected into a live structure under full operational load.
Injection waterproofing is the most technically robust solution available for water ingress in existing concrete infrastructure. Where surface membranes require excavation, dry conditions, and intact substrates, injection works from the accessible interior face under live conditions — permanently sealing active leaks, joints, and pore networks from within the structure.
Among injection materials, the choice comes down to performance requirements and project constraints. For active leaks, extreme temperatures, potable water contact, environmental sensitivity, or dynamic cracks, mineral bentonite gel injection is technically superior to polymer-based alternatives on every relevant specification parameter.
Contact the Euras Technology engineering team for a technical consultation on your project, or book a consultation directly. We provide injection waterproofing specifications, on-site technical support, and product supply for infrastructure projects worldwide.
