Types of Injection Grouting Resin and When to Use Each One
- Jul 28
- 5 min read
Updated: 4 days ago
Not all leaks are the same. Some are caused by a single crack; others are the result of failed waterproofing behind an entire wall. Some structures experience constant pressure from groundwater, while others only leak after heavy rain.
The challenge is that each situation may require a different type of injection grout (or resin) to effectively stop the leak.
Although two resins may look similar, they can behave very differently. Some resins expand to fill voids, some remain flexible, and others are thin enough to travel through hairline cracks or permeate the soil behind a structure.
Choosing the right resin is all about matching the chemistry to the conditions you're trying to solve. Your specialty contractor will ultimately make that decision, but it helps to know what's driving it.
In this guide, we'll break down the main resin types used in injection grouting and explain where each one performs best.
A Quick Recap: What is Injection Grouting?
Injection grouting is a method of filling cracks and voids in concrete, masonry, or soil as a means of stopping leaks.
Chemical grout is pumped into the substrate through a series of small, drilled holes or probes. The grout then travels into the crack or void, where it reacts and forms a barrier that blocks the path of water.
One of injection grouting's biggest advantages is that it can be done from inside the structure, which means you can stop leaks without having to excavate. This is especially important in urban areas like NYC where building owners often don't have the option to excavate, or simply want to avoid the life safety risks that come with it.
How the Right Resin Gets Selected
Different resin chemistries solve different problems, which is why resin selection is one of the first things a contractor works out before starting a job. To choose the right one, they typically work through a handful of questions:
Is water actively flowing?
Is the leak constant or occasional?
Is the crack moving?
Are there voids behind the wall?
What's your goal: waterproofing or stabilizing soil?
What is the intended use of the space?
The answers will point them toward a suitable resin type. Here's what that decision tends to look like:
If your project involves: | Contractors typically consider: |
Active leaks and voids | Hydrophobic polyurethane resins |
Constant moisture and flexible crack sealing | Hydrophilic polyurethane resins |
Curtain grouting or very fine cracks | Acrylate resins |
Soil stabilization or pre-excavation work | Geotechnical resins |
Hydrophobic Polyurethane Resins
Best for Active Water Leaks and Void Filling
Hydrophobic literally means “water-fearing.” This type of resin repels water and requires a catalyst to kick off the reaction. Once it reacts, it expands (sometimes dramatically) and pushes water out of the crack or void as it fills the space.
Because it repels water rather than absorbing it, a cured hydrophobic foam stays dimensionally stable, which means it won't keep swelling or shrinking as moisture levels around it change.
Advantages
Excellent water cutoff
Fills large voids
Adjustable reaction times
Available in flexible or rigid formulations
Can stop high-volume water infiltration
Real-World Scenario
A parking garage wall leaks heavily after every rainstorm. Water is actively flowing through a construction joint, and there are voids behind the wall. The expanding hydrophobic polyurethane resin rapidly reacts with water, fills the voids, and creates an effective water cutoff.
Hydrophilic Polyurethane Resins
Best for Constant Wet Conditions
Hydrophilic means "water-loving." A hydrophilic resin absorbs water as part of its cure reaction, causing the grout to expand significantly. The material swells to fill the void, then cures into a flexible gel or foam.
Instead of pushing water away, these resins interact with moisture and remain compatible with wet environments. That makes them ideal where water is constantly present.
Advantages
Excellent for areas with continuous moisture
Flexible after curing
Good for moving joints
Suitable for long-term groundwater exposure
Real-World Scenario
A below-grade elevator pit has small but constant groundwater seepage through several cold joints. Since the structure remains wet year-round, the flexible hydrophilic polyurethane resin stays compatible with the moist environment and accommodates minor movement.
Acrylate Resins
Best for Curtain Grouting and Hairline Cracks
Acrylate grouts are an entirely different chemistry from polyurethane. Unlike urethanes, acrylates have a minimal expansion rate. These resins have an extremely low viscosity, meaning they're extremely thin and flow like water. This allows them to penetrate tight spaces and cracks that polyurethane resins may not be able to reach. This is why acrylates are commonly used in curtain grouting, where reaching very small cracks and voids matters more than raw expansion force.
Advantages
Extremely low viscosity
Excellent penetration
Adjustable reaction times
Highly flexible
Very durable
Real-World Scenario
A subway tunnel has widespread dampness coming through dozens of hairline cracks, and excavation isn't an option. A contractor would likely turn to acrylate resin here. Its water-like viscosity lets it travel into the finest cracks and form a waterproof barrier behind the structure.
Geotechnical Resins
Best for Soil Stabilization
Instead of waterproofing masonry or concrete structures, geotechnical injection grouts are designed to improve soil conditions before excavation or stabilize loose ground beneath existing structures. They can either be an acrylate or polyurethane formula.
Advantages
Stabilizes weak soils (soil plugs, underpinning)
Improves excavation safety
Used for dewatering - reduces groundwater movement
Supports adjacent structures
Real-World Scenario
A contractor is preparing to excavate next to an existing foundation wall. The surrounding soil is loose and saturated, and there's a risk of it shifting or losing stability once the excavation starts. A geotechnical resin is injected into the soil ahead of time, binding it together and reducing groundwater movement so the excavation can proceed safely without undermining the adjacent structure.
Every Leak is Different
Choosing a resin isn't always straightforward. It depends on the specifics of the leak.
Before choosing a product, experienced contractors will weigh a number of factors: the source of the water, whether the crack is moving, the condition of the substrate, groundwater pressure, how accessible the area is, and the desired long-term performance. A long-lasting solution starts with matching the right chemistry to the right application.
Surface conditions, temperature, and moisture level at the time of injection also affect how well any resin cures, regardless of which one is chosen.
If you're a property owner, architect, or engineer trying to evaluate a proposed scope, or a contractor who wants a second set of eyes on a tricky application, contact us.
We work with contractors, engineers, and waterproofing consultants to evaluate project conditions and recommend the most suitable resin for each application.
