The basic characteristics of epoxy and polyurethane

Epoxy and polyurethane are resins; they are generally two-component formulations. The combination of the components for each type of resin creates the material with the necessary properties for crack repair.

The components of epoxy are a resin and a hardener; mixed before a crack shot. The mixing ratio is typically two parts epoxy to one part hardener. Injection epoxies generally 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 about the properties of cured polyurethane.

Differences in Epoxy and Polyurethane Crack Injection Processes

There are significant differences in how polyurethane and epoxy crack injections are carried out. Epoxy injections are called “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 through the use of packers inserted into holes drilled through the crack in the poured concrete base. Like epoxy, injected polyurethane fills the crack through the entire thickness of the base, thus preventing water from entering the crack. Professional polyurethane crack injections usually involve a flushing process to clean the crack and improve adhesion within the crack.

Advantages of Epoxy Crack Injection

1. The tensile strength of cured epoxy is higher than that of poured concrete. Under stress, 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. The curing time of the epoxy allows the epoxy to be gravity fed into the crack, thus filling all parts, even the hairline cracks.

Advantages of polyurethane crack injection

1. Polyurethane can be used regardless of the condition of the crack and weather. It does not matter if the crack is actively leaking, filled with mud and/or mineral deposits, or if it is small or large.

2. Polyurethane injection involves a crack-washing process that cleans the crack prior to injection.

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

4. The rapid curing of polyurethane is beneficial where rapid waterproofing is required.

Disadvantages of Epoxy Crack Injection

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

2. Epoxy is not suitable for re-injecting failed crack repairs.

3. Homeowner’s basement leak repairs with hydraulic cement or caulk make epoxy injections inappropriate because there is no longer access to the crack surface, mud and/or mineral has accumulated in the crack and concrete around the crack parts is often damaged by water saturation.

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

Note: The strong bond of epoxy is often cited as a negative attribute of epoxy crack injections due to its stiffness. Please note that the entire poured concrete base is rigid; therefore, the need for flexibility in the material used to inject a crack is, in my opinion, 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 does not do well when exposed to significant stress; therefore it is possible for the polyurethane to break if there is excessive stress in a crack, unless reinforced.

2. Unlike epoxy grouting, polyurethane crack grouting does not provide the grouting technician with positive confirmation that the crack has been completely filled.

Reinforcement of foundation cracks

Structural reinforcement of foundation cracks is achieved only by injecting epoxy into the cracks and/or by using carbon fiber reinforcing clips. A cracked basement wall can be structurally reinforced regardless of the injection method used.

Cracks in concrete will be in a state of compression or tension at any time. The state of a crack varies during the year due to the thermal cycle, as well as changes in soil pressure on the foundation wall. Epoxy will not yield to tensile forces; however, polyurethane can tear due to stress within a crack.

The bottom line

Okay, so which method is better for repairing cracks in concrete: epoxy or polyurethane? In my opinion, one should use epoxy crack injections whenever possible. However, the characteristics of the crack to be injected should dictate the method used. If the characteristics of each type of injection are not taken into account, the probability of crack repair failure will increase considerably.

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