Injection epoxy resins and urethane foam systems are the two most widely used materials in the repair of leaking cracks in concrete and gunite pools. Urethane foams have also been recently introduced in the repair of pool skimmers. Both epoxy resins and urethane foams are very generalized terms to the extent that they include systems that are not specifically suited for the type of repair required by pools and skimmers.
Urethane systems developed for the permanent repair of leaking cracks foam as a result of mixing and reacting with water in the crack. They should also have the capability of hardening to a flexible rubber consistency in the absence of water. They should require very little water to foam, and not to begin foaming upon immediately coming in contact with water. They need time to fill most of the crack as a thin liquid (filling tight fissures within the crack) and to be able to leak partially out the back and fill a void, if present.
Ideally, there is just enough foaming in the crack to form a tight, flexible membrane which seals the crack. The less foaming in the crack, the more stable the membrane. At the same time, it should have the capability to expand 20-30 times its initial volume behind the crack if there is a void present. The foam should also be flexible and resilient (how easy is it to poke a hole in it), and not collapsing within a couple of days.
To have all of these characteristics requires a hydrophobic foam (which needs little water and is capable to have a free rise of 20-30 times its initial volume). It needs the isocyanate/ polyol reaction to be reacting independently of the presence of water (so that a reacted rubber membrane can still form even in the absence of water). Therefore, it should be a two-component system. It should approach the flexibility and resilience of a hydrophilic urethane (but without the shrinkage associated with hydrophilic systems, which also need much water and do not sufficiently expand to be practical in filling any significant voids).
Emecole has developed such a system, Emecole 102. It is available in a single cartridge (designed to hold part A and Part B separately in its chamber until the reaction is to take place). This cartridge is a recent development and can dispense its contents through a static mixer with an ordinary caulk gun. For the professional who would utilize greater usage of Emecole 102, it is available in dual cartridges which require a dual cartridge tool. Finally, it is also available in 5-gallon units as well as 55 gallon drums for large usage applications using meter/dispensing equipment.
It should be understood that urethane foams were originally developed to just stop the flow of water. Such foams did not need to remain structurally stable over time. Most such systems are not suitable for crack repair, as such a repair involves more than just stopping water leakage now. It is the permanent repair of a structure. Most existing suppliers offer products for just stopping water; make sure you use a product that is designed to be a permanent fix and has a history to support such requirements.
These characteristics are especially relevant in skimmer repair. Skimmer repair involves the introduction of Emecole 102 into the skimmer throat. It then must flow throughout the entire skimmer system, filling both large voids and small fissures. It expands to its fullest and must remain stable without having foam-cell collapse over time. For it to effectively seal the skimmer, Emecole 102 must be able to flow a significant distance as a fluid and foam as slowly as practical (being able to reach all the fissures and voids).
Epoxy repair of a crack is typically associated with situations where structural integrity needs to be enhanced. A system repaired with epoxy will result in strengthening the overall structure. Urethane foam systems cannot accomplish strengthening without the use of carbon fiber (more on this later). Urethane foams are best suited when the only repair required is the stopping of a leak in an otherwise structurally sound structure.
Injection epoxies can fail in situations where there is a void behind the crack. An injected epoxy takes hours to harden within a crack. As a consequence, it remains fluid during this time and can leak out the back, leaving the crack with insufficient epoxy to effect a repair. To overcome this, Emecole 121 was developed, which begins to harden within 5-20 minutes after injecting (even in hairline cracks). Even if some material begins to leak out, the applicator has time to detect this and add more epoxy.
Epoxies, alone, cannot solve an on-going structural problem such as when the settlement stresses are exceeding the strength of the area around the crack in question. These are circumstances that require the introduction of carbon fiber strapping or stitching (depending on the extent of the problem). Emecole offers such systems and the know-how as to when and how they need to be used.
The process used with either urethane foams or injection epoxies requires the application of a surface seal (such as Emecole 301). With many pool applications, it is required that the surface seal be removed for aesthetic reasons. This can be done, with difficulty, by grinding or chipping of the surface seal. To overcome this, Emecole 322 has been introduced. This surface seal can be effectively peeled off after the crack repair is completed.
Emecole 455 is a very unique product. It is an excellent adhesive bonding plastic, concrete, and/or steel equally well. It reacts very fast, and is also sometimes used as a surface seal.
For more information, go to www.emecole.com