Epoxy or Polyurethane Crack Injection – What’s Best?

The Basic Characteristics of Epoxy and Polyurethane

Epoxy and polyurethane are both resins; generally, they are two component formulations. The blending of the components for each resin type creates the material with the requisite properties for crack repairs.

Epoxy’s components are a resin and a hardener; blended together before a crack injection. The mix ratio is typically two parts epoxy to one part hardener. Injection epoxies typically cure within three to four hours. Once cured, epoxy has a strong bond and a hard plastic-like texture.

Polyurethane, while not necessarily a two component blend, typically has two; one is the resin and the other is an accelerator. Unlike epoxy, the texture of cured polyurethane varies significantly; one cannot generalize regarding the properties of cured polyurethane.

Differences in The Epoxy and Polyurethane Crack Injection Processes

There are significant differences in how polyurethane and epoxy crack injections are carried out. Epoxy injections are referred to as “Surface port injections” because they involve the use of injection T-Ports to inject the epoxy into a crack.

Polyurethane injection involves much higher injection pressures using packers inserted into drilled holes through the crack in the poured concrete foundation. Like epoxy, the injected polyurethane fills the crack through the entire thickness of the foundation thereby preventing water from entering the crack. Professional polyurethane crack injections typically involve a flushing process to clean the crack to improve adhesion within the crack.

Advantages of Epoxy Crack Injection

1. The tensile strength of cured epoxy is greater than that of poured concrete. Under tension, cured epoxy crack repairs will not yield.

2. Epoxy injections provide positive confirmation to the injection technician that the crack has been completely filled.

3. Epoxy crack injections are extremely reliable due to their low failure rate.

4. Epoxy’s curing time allows the epoxy to gravity feed within the crack, thereby filling all parts of even the finest cracks.

Advantages of Polyurethane Crack Injection

1. Polyurethane can be used regardless of the crack condition and the weather. It doesn’t matter if the crack is actively leaking, full of mud and/or mineral deposits, or if it is small or large.

2. Polyurethane injection involves a crack flushing process that cleans out the crack prior to the injection.

3. The chemical expansion of the polyurethane will fill voids within the concrete.

4. The rapid curing of polyurethane is beneficial when rapid waterstopping is required.

Disadvantages of Epoxy Crack Injection

1. Moisture adversely affects the adhesive qualities of the anchoring epoxy used to adhere the T-Ports onto the crack. Without sufficient adhesion, the anchoring epoxy will not withstand the injection pressure.

2. Epoxy is inappropriate for re-injecting previously injected crack repairs that have failed.

3. Homeowner basement leak repairs with hydraulic cement or caulking render epoxy injections inappropriate because there is no longer surface access to the crack, mud and/or mineral has built-up in the crack, and the concrete around parts of the crack is often damaged by water saturation.

4. The curing time and the available viscosities of epoxy are positive attributes, but also weaknesses. Epoxy crack injection relies on the containment of epoxy within a crack until the epoxy has cured. This containment uses the compacted soil against the outside wall. Poor compaction, air-gap membranes and the use of epoxies with insufficient viscosity will result in the bleeding of epoxy into the soil.

Note: The strong epoxy bond is often cited as a negative attribute of epoxy crack injections due to its rigidity. Keep in mind that the entire poured concrete foundation is rigid; therefore, the need for flexibility in the material used to inject a crack, in my opinion, is illogical as there is no real need to accommodate crack movement.

Disadvantages of Polyurethane Crack Injection

1. While polyurethane is flexible and can absorb compressive force it doesn’t fare well when exposed to significant tension; consequently, it is possible that polyurethane will tear if there is excessive tension in a crack, unless it is reinforced.

2. Unlike the epoxy injection, polyurethane crack injection doesn’t provide the injection technician with positive confirmation that the crack has been filled completely.

Foundation Crack Reinforcement

Structural reinforcement of foundation cracks is either accomplished by epoxy crack injection alone and/or by using carbon fibre reinforcing staples. A cracked basement wall can be structurally reinforced regardless of the injection method used.

Concrete cracks will either be in a state of compression or tension at any time. The state of a crack varies during the year due to themal cycling as well as the changing soil pressure on the foundation wall. Epoxy will not yield to tensile forces; however, polyurethane may tear due to tension within a crack.

The Bottom Line

OK, so which method is best for repairing cracks in concrete: epoxy or polyurethane? In my opinion, one should use epoxy crack injections wherever possible. However, the characteristics of the crack to inject should dictate the method used. Failure to take into account the characteristics of each injection type will considerably increase the probability of crack repair failure.

For a more detailed comparison of both crack injection methods visit our website at www.aquaguardinjection.com