Injecting life back into precast

Michael Vargo, Prime Resins Senior Technical Consultant

I had the privilege of presenting a course on pressure injection of concrete to repair cracks and seal leaks at the NPCA Precast Show 2015 Orlando. I explained pressure injection and the techniques, equipment and accessories needed to perform pressure injection of epoxy and polyurethane resins.

If you’d like a copy of my presentation, email me at, but here’s a brief overview of what it covers.

In a nutshell, if you:

• Select the right resin
• Select the right equipment
• Follow proper procedures and
• Have patience

You will:
• Get great finished results

Precast comes in all shapes and sizes, and there are many possible causes of cracks in precast, including poor casting, damage in handling and transport or unloading.

Pressure injection is a method to repair cracks in concrete, wood or other materials. The repair is done by forcing an adhesive resin, such as epoxy, into a crack where it can cure and “weld” the material back together.

I include the ACI 224-01 Control of Cracking in Concrete Structures guide to reasonable crack widths for reinforced concrete under service loads.

Generally we use epoxy for structural repair and polyurethane for non-structural/leak repairs.precast

Choosing the right resin is absolutely critical to a successful job. Criteria include:

  • Required strengths
    • Compressive
    • Tensile
    • Bond
    • Flexural
  • Crack size (depth, width)
  • Temperature of the concrete
  • Working time needed

Resins are classified according to ASTM Standard C-881 (American Society for Testing & Materials). The elements include:

  • Type – Intended Uses (Strengths): 5 types and how they are tested
  • Grade – Viscosity (Flowability): 3 grades and their cps ranges
  • Class – Usage Temperature Range: 3 classes and the temperature ranges

Why is a resin’s type important?
The “type” informs the customer that the cured epoxy will have the strength properties required for typical applications. For some uses, particularly those requiring high strengths, it may be necessary to choose a resin based on its compressive, bond, tensile and/or flexural test results. A resin can be more than one type.

Why is the grade important?
The grade indicates how easily the resin will flow into or through a crack. Because a resin has one viscosity, which is tested with a viscometer, it can only be classified as a single grade.

Why is the class important?
Finally, you may need to know the temperature at which an epoxy resin can be used, which is shown by a resin’s class. Some epoxy resins can be used in more than one temperature range and may therefore be in two classes.

Most injection specs will read:

ASTM C-881
Type I or IV (For Bonding Hardened Concrete to Hardened Concrete)
Grade 1 (Low Viscosity)
Class B and C (40°F or 4.4°C and above)

Considering potlife: properties of the product, conditions, equipment, job parameters
Determining the pressure for injection
Picking pumping equipment, high or low pressure
Selecting your pump and examples of types
Selecting a port system and examples

Next I provide step by step instructions for injecting cracks with epoxy resins, including photos illustrating the steps.

Then I provide step by step instructions for crack injection with polyurethane resins. This starts with choosing which type, hydrophobic (repels water) or hydrophilic (seeks water).

Other factors to weigh include the presence and volume of water, and the width and depth of the crack.

I provide instructions for sealing very wide cracks or joints and how to seal manholes.

Again, if you make the right decisions up front and use the proper techniques, you should have a successful outcome. If you have questions, feel free to call me at 800-321-7212.

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