Among waterproofing contractors within the Greater Toronto Area, and on many websites worldwide, there are differing opinions as to which type of crack injection method (epoxy vs polyurethane) is the best. In an attempt to put an end to this controversy, this page was written by one of our very experienced injection technicians with a mandate of providing the community at large with an objective and unbiased comprehensive comparison of the characteristics of each type of foundation crack injection, detailing their advantages and disadvantages.
Table of Contents
The Basic Characteristics of Epoxy and Polyurethane
Differences in The Epoxy and Polyurethane Crack Injection Processes
The Advantages of Epoxy Crack Injection
The Advantages of Polyurethane Crack Injection
The Disadvantages of Epoxy Crack Injection
The Disadvantages of Polyurethane Crack Injection
Foundation Crack Reinforcement
The Bottom Line
The Basic Characteristics of Epoxy and Polyurethane
Epoxy and polyurethane are collectively referred to as resins; for the most part, both are two component formulations. The blending of the 2 components for each resin type creates a material with the requisite properties for professional crack injection repairs.
In the case of epoxy, one component is the epoxy resin and the second is a hardener; both are blended together immediately before a crack injection. The mix ratio is typically 2 parts epoxy to 1 part hardener. Most injection epoxies fully cure within 3-4 hours at a temperature of 77° Fahrenheit or 25° Celsius. Epoxy is comparable to glue; once cured, it has a strong bond and a hard plastic-like texture.
Polyurethane, used in the context of foundation crack repairs, while not necessarily a 2 component blend, typically has 2 components; one is the polyurethane resin and the other is an activator, or accelerator. Like epoxy, the 2 components are mixed before they are injected into a foundation crack. Unlike epoxy, the texture of cured polyurethane varies significantly due to varying polyurethane formulations; there are many in the marketplace. Like epoxy, polyurethanes have various viscosities depending on the formulations used. Some cured polyurethane formulations become very rigid, some are powdery, others are rubbery, etc. The polyurethane formulations vary among manufacturers so one cannot generalize regarding the properties of cured polyurethane. To accommodate crack tension and compression we believe that the best polyurethane resin cures with a rubber-like consistency. The rationale behind our recommended consistency for cured polyurethane is discussed later. The cure time associated with polyurethane does vary, even among crack injections using the same formulation. The cure time is generally 15 - 45 minutes and is influenced by both temperature and humidity.
Differences in The Epoxy and Polyurethane Crack Injection Processes
There are significant differences in how polyurethane crack injections vs epoxy crack injections are carried out. Epoxy crack injections are referred to as "Surface port injections" because they involve the use of injection T-Ports to inject the epoxy into a crack. Click here for more detail on how an epoxy crack injection is performed.
Polyurethane injection involves the high pressure (typically 1500 psi) injection of activated polyurethane through injection packers inserted into 8" deep drilled holes through the crack in the poured concrete foundation wall. Like epoxy, the injected polyurethane fills the crack through the entire thickness of the foundation wall (typically 8") thereby preventing water from entering the crack. A professional polyurethane crack injection typically involves a flushing process which cleans the crack to ensure good adhesion of the polyurethane to both sides of the crack. Click here for more detail on how a polyurethane crack injection is performed.
The Advantages of Epoxy Crack Injection
1. The tensile strength of cured epoxy is typically 7000 psi whereas the tensile strength of concrete is in the range of 300 - 700 psi; clearly, the bond strength of epoxy is much greater than that of the foundation wall. When tension is applied to a crack due to thermal cycling or the retraction of the soil against the exterior of the foundation wall, the cured epoxy crack repair will not yield. In most cases, an epoxy crack injection will also not yield to crack tension attributable to excessive loading of the foundation. This excessive loading generally will be found where I-beams are located.
Note: When a crack is under tension it opens up; therefore, a material that cannot withstand the tension will tear. Epoxy is the best material to use when a crack is under tension; however, a reinforced polyurethane crack injection will work just as well.
2. The process by which an epoxy injection is done provides positive confirmation to the injection technician that the crack has been completely filled.
3. Epoxy crack injections (done by properly trained technicians in possession of suitable epoxies) are extremely reliable due to their low failure rate.
4. The curing time allows the epoxy to gravity feed within the crack, thereby filling all parts of even the finest cracks.
5. Epoxies can be obtained in various viscosities to suit very fine to very large cracks. Furthermore, it is possible to lower the viscosity of the epoxy on-site in order to properly fill very fine hairline cracks.
The Advantages of Polyurethane Crack Injection
1. Polyurethane can be used regardless of the condition of the crack 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 (typically 5 times it's original volume) makes polyurethane very effective at filling voids within the concrete; these voids are typically invisible when you look at the wall and are often associated with the porosity of the concrete.
4. Occasionally, high injection pressures are required to fill cracks that are either very fine or when concrete is completely saturated with water and therefore weak. Since professional polyurethane injections are carried out using electric pumps, it is possible to use injection pressures up to 3200 psi.
5. The rapid curing of polyurethane is beneficial when a leaking crack is flooding the basement; this is an important attribute when rapid waterstopping is required;
6. Unlike epoxy crack injection, polyurethane crack injection does not provide the injection technician with positive confirmation that the crack has been filled completely; however, given it's accelerated reactivity in the presence of water, a polyurethane crack injection can be tested while the injection is in progress. The flooding of the wall required to perform this testing provides positive confirmation that the repaired crack does not leak.
The Disadvantages of Epoxy Crack Injection
1. Since an epoxy injection is a surface port injection, the injection ports must adhere to the wall surface, directly on the crack, with a very strong bond. 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 (also referred to as thixotropic paste) will not withstand the pressure of the injection. If a crack is leaking or if the surface of the wall is damp or wet, the paste will not adhere well to the crack surface and therefore, an epoxy crack injection cannot be done reliably.
2. Another instance in which epoxy crack injection is inappropriate pertains to the re-injection of previously injected crack repairs that have failed. If an injection has failed, it is logical to assume that there is residual injection material within the crack; this being the case, injected epoxy may be prevented from travelling along the full length of the crack. Under these conditions it is prudent to use an injection material with expansive properties to ensure that whatever voids remain in the crack, and are therefore likely responsible for the ongoing leaking of the crack, will be filled.
3. Quite often homeowners attempt to repair basement leaks by using hydraulic cement or caulking; such repairs make epoxy injections inappropriate for several reasons: there is no longer clear 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 due to saturation that resulted from the trapped water in the crack.
4. While the curing time and the available viscosities of epoxy are viewed as positive attributes of epoxy crack injection, they are also weaknesses. Epoxy crack injection relies on the containment of epoxy within a crack until the epoxy has cured. This containment relies upon the compacted soil against the outside wall. Poorly compacted soil, the presence of air-gap damp-proofing membranes and the use of epoxies with insufficient viscosity are conditions that will result in the bleeding of epoxy into the soil. Obviously, if the epoxy bleeds into the soil the injection has failed.
Note: The strong bond of epoxy is often cited as a negative attribute of epoxy crack injections because cured epoxy is inflexible. While this is a factual statement, one must 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 our opinion, is illogical as there is really no need accommodate crack movement. In residential construction, no design allowances are made to accommodate expansion and contraction of poured concrete. In commercial construction, expansion joints are used to allow for expansion and contraction of poured concrete structures; this design feature is seldom found in residential foundation construction.
The Disadvantages of Polyurethane Crack Injection
1. While polyurethane is flexible and can absorb compressive force it does not do well when exposed to significant tension; consequently, it is possible that polyurethane will tear if there is excessive tension on the crack, unless it is reinforced. Follow this hyperlink for details on crack reinforcement.
2. Unlike epoxy crack injection, polyurethane crack injection does not provide the injection technician with positive confirmation that the crack has been filled completely. During warmer weather this is not usually a problem because the crack can be tested while the crack repair is in progress; however, during cold weather it is not really possible to flood the wall during the crack injection.
Foundation Crack Reinforcement
Structural reinforcement of a foundation crack is either accomplished by epoxy crack injection alone if a crack is less than 3mm wide, and/or by using carbon fibre reinforcing staples. Therefore, a cracked basement wall can be structurally reinforced regardless of the crack injection method used.
The strength and/or flexibility of epoxy and polyurethane injections are often presented to homeowners as important considerations when they sell crack injections.
Concrete cracks will either be in a state of compression or tension at any point in time. The state of a crack varies over the course of a year due to themal cycling of the concrete as well as the changing soil pressure on the foundation wall. Many waterproofing contractors will argue that a flexible polyurethane is best because it compresses well when a crack is in a state of compression. While this is a true statement, it really doesn't matter because, while epoxy will not compress, neither will the rest of the concrete wall; therefore, we don't believe that the ability of a material to absorb compressive forces should be taken into account when deciding on the type of crack injection method to use. In fact, the more important issue is the material's ability to handle tensile forces when cracks tend to open up. Epoxy will not yield to tensile forces; however, polyurethane will tear if there is too much tension within a crack.
The Bottom Line
OK, which method is best for repairing cracks in concrete: epoxy or polyurethane? In our opinion, we would use epoxy crack injections wherever possible. However, the characteristics of the crack to inject should dictate the method to choose. For example, if a crack requires a structural repair we would use epoxy if all of the conditions that are required for an epoxy injection are met. If not, epoxy crack injection would not be feasible; therefore, a polyurethane injection would be done. If reinforcement was required, we would use reinforcing staples to stablize the crack in order to compensate for polyurethane's inability to withstand tensile forces. Similarly, if a crack is full of mud, we would elect to inject the crack with polyurethane to take advantage of the crack flushing process associated with this injection method.
Ultimately, the characteristics of the crack to be repaired should dictate the type of crack injection to be used. The failure to take into account the characteristics of each injection type is likely to considerably increase the probability of crack repair failure.