Water seeping through a basement retaining wall, standing water in an elevator pit or a pressurised leak at a cold joint is usually discovered only after external intervention is no longer an option. Excavating around a building to waterproof it from outside is often technically or economically unfeasible for buildings on shared party walls, properties in active use and deep basements. This is exactly where injection waterproofing comes in: a method applied from the inside that reduces the need for extensive breaking or excavation, targeting the crack carrying the water at its source.
Polyurethane injection works by pumping resin under pressure into cracks and voids in the concrete. On contact with water the resin reacts rapidly and expands, travelling into the finest capillaries of the crack and physically filling the path the water follows. In suitable conditions this makes it possible to intervene even while water is still flowing; the exact time depends on the crack, water pressure and resin used. For hairline cracks and diffuse, large-area seepage, low-viscosity acrylic gel injection systems are preferred instead.
EREL Yalitim, with its engineering-driven approach, has been carrying out waterproofing across Istanbul for over 20 years from its Esenyurt base. Injection is, at its core, resin chemistry: which material, at which viscosity and with which reaction time, is sent into which crack determines whether the application succeeds. That is why on our projects we select injection systems from leading global manufacturers through an engineering assessment of the water pressure and crack geometry on site.
Where Is Injection Waterproofing Needed?
Injection is an effective repair method assessed at the site survey wherever external (positive-side) waterproofing is impossible or not suitable. It allows a building in use to be waterproofed without emptying the basement, excavating the perimeter or extensively breaking the concrete. Because the side the water comes from cannot be reached, these applications fall under negative-side waterproofing; correct diagnosis, system selection and application aim for long-lasting sealing performance.
Concrete crack injection is not limited to cracks that leak water; it is also applied at weak points such as shrinkage cracks, cold joints and tie-rod (formwork tie) holes. The applications we encounter most often are:
The elevator pit is the most critical point in buildings located where the groundwater table is high: as the deepest level of the structure, it is where water appears first. Since the pit cannot be reached from outside, elevator pit injection is one of the main methods considered where external access is not possible.
- Crack and cold-joint leaks in basement retaining walls
- Pressurised water entering at the foundation–wall construction joint
- Stopping water accumulating in elevator pit floors and walls
- Active leaks in car parks, ramps and retaining walls
- Joints and cracks in engineering structures such as water tanks, treatment plants and tunnels
- Expansion joints where tape repair is not feasible
- Hairline cracks in raft foundations under groundwater pressure
Polyurethane, Acrylic Gel and Epoxy Injection: Comparing the Systems
The success of an injection depends largely on resin selection; there is no single right material for every crack. Polyurethane injection resins fall into two main groups: fast-reacting foams that expand rapidly on contact with water, and elastic resins that cure into a flexible, closed-cell seal. In a crack with actively flowing water, the flow is first stopped with foam and permanent watertightness is then achieved with elastic resin; this two-stage approach is the accepted practice in the industry.
Acrylic gel injection, with a viscosity close to that of water, penetrates hairline cracks and porous zones that polyurethane cannot enter. Injected behind a retaining wall, it forms a gel curtain between the structure and the ground, cutting the water off before it reaches the building; this method is preferred for large-area seepage with no identifiable point source. Epoxy injection, by contrast, is a matter of structural repair rather than waterproofing: in dry or dried-out cracks it restores the monolithic integrity and load transfer of the concrete.
On our projects we work primarily with leading global manufacturers' injection resins and systems. We choose materials on site, not from a catalogue: crack width, water pressure, the age of the concrete and whether the joint is moving are measured and assessed before the system is specified.
- Fast-foaming polyurethane: sealing pressurised, active leaks; reacts within seconds to minutes
- Elastic polyurethane resin: permanent, flexible sealing of moving cracks and joints
- Acrylic gel: hairline cracks, porous concrete and behind-wall gel curtain applications
- Epoxy resin: restoring cross-sectional integrity in structural cracks
- Micro-cement injection: filling large voids and ground improvement where required
Active Leak Sealing: How Injection Is Applied Against Pressurised Water
Injecting while water is actively flowing is the most critical and experience-intensive form of the method. Holes are drilled at a set angle to intersect the crack, injection valves known as packers are fitted, and resin is pumped into the crack at a pressure high enough to overcome the water pressure. The moment the resin meets water it begins to foam; the expansion pressure back-fills the water's path and cuts off the flow.
Pressure management is decisive throughout this process. Excessive pump pressure can widen the crack or drive the resin beyond the target zone; too little pressure prevents it from reaching the capillaries. On EREL Yalitim sites, injection is carried out with single- and two-component pumps, with continuous pressure monitoring and packer spacing calculated from the crack geometry. Once the flow stops, the area is rechecked; where necessary, a second injection pass feeds in elastic resin.
Our track record on corporate projects is the product of this discipline: our injection work is likewise carried out to specification, based on a documented site survey, and at measurable quality.
The EREL Yalitim Difference in Non-Destructive Waterproofing
Injection is a trade in which application knowledge matters more than the material itself. Two crews using the same resin can get entirely different results, because reaction time varies with ambient temperature, the amount of water and the mixing ratio. Our team's chemical engineering background means resin behaviour is read correctly on site: which catalyst ratio to work with at which temperature is determined by technical data, not guesswork.
We never start injecting before diagnosing the source of the leak. The point where water appears and the point where it enters the structure are rarely the same; injection at the wrong point does not stop the water, it merely redirects it. During the survey a crack map is prepared, water pressure and flow rate are assessed, and the application is documented in a report. On completion, you receive a written record of which material was used where.
We work turnkey: drilling, injection, packer removal and surface repair are all handled by the EREL Yalitim team. In occupied buildings, noise, dust and disruption are kept to a minimum; most applications are completed in the basement without interrupting daily life.
Our Application Process
- 1
Survey and Leak Diagnosis
The point where the leak is visible and the point where water enters the structure are identified separately; crack width, water pressure and the condition of the concrete are assessed on site. The survey is free of charge.
- 2
System Design and Material Selection
Based on the crack geometry and water conditions, a polyurethane foam, elastic resin or acrylic gel injection system is specified; packer spacing and the injection sequence are planned.
- 3
Drilling and Packer Installation
Holes are drilled at a set angle to intersect the middle of the crack, and injection packers are fitted to form a watertight seal.
- 4
Surface Preparation and Sealing the Crack Mouth
Where needed, the mouth of the crack is closed with rapid-setting repair mortar to prevent uncontrolled resin backflow.
- 5
Pressurised Resin Injection
Resin is injected in stages with a pump, starting from the lowest packer; pressure and resin consumption are monitored throughout the application.
- 6
Watertightness Check and Second Pass If Needed
Once the reaction is complete, the area is inspected; if required, a second-stage injection with elastic resin secures long-term watertightness.
- 7
Packer Removal, Surface Repair and Handover
Packers are removed, holes are filled with repair mortar, the surface is levelled and the job is handed over together with an application report.
Frequently Asked Questions
How is polyurethane injection priced?
Injection is not priced per square metre; the price is set by parameters such as crack length (linear metres), the number of packers, resin consumption and water pressure. Any figure quoted without seeing the site is misleading. EREL Yalitim carries out the survey free of charge and follows it with a written, itemised quotation.
Is injection a permanent solution or a temporary one?
Injection with the right resin at the right point provides a permanent seal. For active leaks, the key to durability is applying a second, elastic-resin stage after the flow has been stopped with foam. If the wrong material or the wrong point is chosen, the water finds a new path — which is why diagnosis before the application is the most critical step.
Can the application be carried out while water is actively flowing?
Yes; this is precisely the scenario where polyurethane injection is strongest. On contact with water the resin foams and expands and can reduce pressurised flow quickly; the exact time depends on the crack and water pressure. There is no need to wait for the leak to dry out before active leak sealing.
Does the application involve demolition, and does the basement need to be emptied?
No. Injection is a non-destructive waterproofing method; only finger-width injection holes are drilled, and they are filled with repair mortar at the end of the job. The application can proceed while the basement, car park or business remains in use.
Will injection solve standing water in an elevator pit?
Yes; elevator pit injection is among the jobs we carry out most often. Since the pit cannot be reached from outside, we work from the inside, on the negative side; the floor–wall junction and cracks are filled with resin so the water is cut off at its source. The application is scheduled in coordination with the elevator company.
Should I choose polyurethane or acrylic gel?
The decision depends on the state of the crack and the water. Polyurethane is the right answer for pressurised, active flows and well-defined cracks; acrylic gel injection performs better in hairline cracks, porous concrete and diffuse seepage with no clear source. Both systems are evaluated during the survey and, where necessary, used together.