Types of Injection Grouting Resin and When to Use Each One
Updated: Sep 17
Not all leaks are the same. One may be coming through a single crack or joint. Another may be the result of failed waterproofing behind an entire wall. Some structures deal with constant groundwater pressure, while others only leak after a heavy rain.
And that's why there isn't one injection grout (or resin) that works for every job.
Although two resins may look similar, they can behave very differently. Depending on the resin, it may expand to fill a void, stay flexible after curing, or travel through very fine cracks and into the soil behind a structure.
Before selecting a resin, you need to know what’s causing the leak and what you need the grout to do.
Injection Grouting Basics
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 major advantage of injection grouting is that it can be done from inside the structure without having to excavate. That's useful in dense, urban environments like NYC, where excavation can be difficult, expensive, disruptive, or simply not practical.
How the Right Resin Gets Selected
Different resin chemistries solve different problems. So, before choosing a resin, you and your injection grouting contractor need to understand exactly what you're dealing with.
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 help you narrow down your options.
If your project involves: | Contractors typically consider: |
Active leaks and larger 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 |
Of course there’s more to resin selection than this chart, but it gives you a good place to start. Let’s look at each type a little more closely.
Hydrophobic Polyurethane Resins
Best for Active Water Leaks and Void Filling
Hydrophobic literally means “water-fearing,” which tells you something about how these resins work. This type of resin repels water and requires a catalyst to kick off the reaction.
Once injected, the resin reacts and expands (sometimes dramatically), pushing water out as it fills the crack or void. Depending on the formulation and catalyst ratio, that reaction can happen quickly, which makes it particularly useful when you're trying to shut down actively flowing water.
It can also expand considerably, so it's often a good fit when the leak involves more than a tight crack and there are larger voids that need to be filled.
Once cured, the foam repels rather than absorbs water and remains dimensionally stable as moisture conditions change.
Why contractors use it:
Excellent water cutoff
Fills large voids
Adjustable reaction times
Available in flexible or rigid formulations
Can stop high-volume water infiltration
Example
Say a parking garage wall leaks heavily after every rainstorm. Water is actively flowing through a construction joint, and there are voids behind the wall. A hydrophobic polyurethane resin can be injected into the joint and surrounding voids, where it reacts and expands, creating an effective water cutoff.
Hydrophilic Polyurethane Resins
Best for Constantly Wet Conditions
Hydrophilic means "water-loving." Instead of repelling water, these resins absorb water as part of their reaction, and then cure into a flexible foam or gel. They're commonly used in areas that remain wet and in cracks or joints where some movement is expected since they remain flexible after curing.
Why contractors use it:
Works well in areas with continuous moisture
Remains flexible after curing
Can accommodate movement in cracks and joints
Suitable for long-term groundwater exposure
Example
A below-grade elevator pit has a small but constant amount of groundwater seeping through several cold joints. Since the area remains wet year-round, the flexible hydrophilic polyurethane resin stays compatible with the damp environment and accommodates minor movement.
Acrylate Resins
Best for Curtain Grouting and Hairline Cracks
Acrylate grouts are an entirely different chemistry from polyurethane.
They have a minimal expansion rate and are extremely low in viscosity, meaning they're very thin and flow like water. This allows them to travel through fine cracks and tight spaces that polyurethane resins may have trouble reaching. This is why acrylates are commonly used in curtain grouting, where reaching very small cracks and voids matters more than raw expansion force.
Why contractors use it:
Extremely low viscosity
Can penetrate very fine cracks
Adjustable reaction times
Highly flexible
Well suited to curtain grouting
Example
Picture a subway tunnel with widespread dampness coming through dozens of hairline cracks. Excavation isn't an option. An acrylate resin can be injected through the structure, where it travels behind the wall into the finest cracks, and forms a waterproof curtain across a broad area.
Geotechnical Resins
Best for Soil Stabilization
Injection grouting can also be used to treat the soil itself.
Geotechnical injection grouts are designed to improve soil conditions before excavation, stabilize loose ground beneath existing structures, and reduce groundwater movement. Depending on the application, they may be polyurethane- or acrylate-based.
Why contractors use it:
Stabilizes weak or loose soils (soil plugs, underpinning)
Improves excavation safety
Used for dewatering - reduces groundwater movement
Stabilizing soil around existing structures
Example
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 can be 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
The truth is, choosing a resin isn't always straightforward. You also have to consider the source of the water, movement, substrate conditions, groundwater pressure, access, voids, and what you're trying to accomplish with the injection.
Sometimes the choice is obvious. Sometimes it isn't.
If you're evaluating a proposed scope or trying to figure out which resin makes sense for a difficult application, give us a call. We work with contractors, engineers, waterproofing consultants, and building owners to evaluate project conditions and recommend an appropriate resin for the job.
