Hydrophilic vs. Hydrophobic Polyurethane Resins: Choosing the Right Solution for Leak Sealing and Crack Injection
When it comes to waterproofing concrete structures, polyurethane resins are one of the most reliable and adaptable solutions available. However, not all resins are the same.
The two main categories: hydrophilic and hydrophobic, behave very differently once injected, and selecting the wrong type can compromise performance.
Here’s what construction engineers, specifiers, and project managers need to know.
Hydrophilic Resins: Flexible, Water-Loving Seals
Hydrophilic resins seek out water. When injected into cracks, joints, or voids, they absorb water and expand to form a flexible gel or foam. Best for:
Hairline cracks (as small as 0.05 mm)
Cold climates with freeze–thaw cycles (Canada, northern U.S.)
Moving joints and dynamic cracks
Areas where flexibility is critical to absorb structural movement
Advantages:
Penetrates extremely fine cracks
Expands with moisture and maintains contact even as concrete moves
Long service life in environments with repeated expansion and contraction
Hydrophobic Resins: Durable, Water-Repelling Barriers
Hydrophobic resins repel water. They expand quickly into a rigid, closed-cell foam, creating a strong barrier against water intrusion.
Best for:
Active leaks under high hydrostatic pressure (tunnels, dams, basements)
Marine/coastal applications (Caribbean seawalls, retaining walls)
Large void filling and high-volume crack injection
Dry or low-moisture conditions where flexibility is less critical
Advantages:
High expansion rate for filling voids
Permanent watertight seal, even in fast-moving leaks
Resistant to salts, chemicals, and aggressive environments
Environments & Uses:
Canada (freeze–thaw, salt, corrosion risk): Hydrophilic resins are often preferred for joints and hairline cracks in garages, basements, and foundations.
Caribbean (marine, seawalls, high humidity): Hydrophobic resins are ideal for sealing against aggressive saltwater intrusion.
South America (tropical rainfall, soil movement): Projects may require a combination approach, using hydrophilic resins for fine cracks and hydrophobic resins for larger voids and high-flow leaks.
The Sustainable Advantage
Polyurethane resins are environmentally advanced compared to traditional coatings and mortars:
Targeted injections = less material waste
Long service life reduces future repair cycles
Low VOC options available, safe for potable water use
Suitable for LEED-type sustainable construction goals
Final Word
Hydrophilic and hydrophobic polyurethane resins each have a clear role in waterproofing concrete infrastructure.
By matching the resin type to the project’s environmental and structural conditions, engineers and project managers can deliver sustainable, long-lasting waterproofing solutions that outperform traditional methods.
Learn more about advanced crack injection and leak seal systems on our Products Page.
