January 1, 2010
By Lance Anderson
The past several years of weak pool construction activity, especially in the U.S., has highlighted the value of identifying alternative revenue sources for pool industry professionals. Finding and fixing leaks in existing swimming pools has become an area of great interest as it provides pool builders with several options for specialization and many opportunities to generate revenue. One such opportunity is crack repair in concrete pool shells.
When dealing with a leaking concrete pool, the leak professional and customer are faced with several repair options, including simple topical repairs (performed while the pool remains filled), permanent crack injections or extensive concrete removal and structural re-engineering. Method selection should be based on the severity of the crack, permanence of the desired repair and customer budget.
A number of things can cause cracks; some are the result of poor workmanship or the materials used during construction. These cracks usually appear soon after construction and are generally not the leak professionals responsibility.
Cracks that develop in older pools and result in water loss, however, are a different story. The first step in any repair job is to try to understand what caused the problem in the first place, and determine if this force will continue causing crack movement in the future. If the crack, for instance is a result of a one-time event, such as an extremely cold winter or shell movement due to the pool being left empty for a long period of time, little additional movement should be expected. However, if it is caused by re-occurring ground expansion and contraction (e.g. soils that expand when moist and shrink when dry), continued crack movement should be anticipated and any repair should take this into consideration. The most serious problems result from ground conditions that are continuously undermined and are expected to continue degrading thus causing cracks to continue growing.
While some of these problems can be solved with tools and techniques available to the average leak professional, situations involving erosion or slope creep (where a pool may be built on a hillside and the supporting soil settles downhill) are generally handled by a structural or soil engineer.
The simplest and least expensive type of crack repair is a topical patch. These repairs are applied to the surface of the crack and can be made with a variety of epoxies and sealants, many of which can be applied underwater. Epoxy putty is a two-part material kneaded together by hand to form a clay-like substance leak professionals can work into cracks with their fingers. Epoxy putty can be applied underwater and easily matched to the pool surface. However, since it is non-flexible when cured, future crack movement will undermine the repair. These repairs often require annual attention.
Rubber- or silicone-based sealants can also be used for simple surface repairs. While some can be used underwater, most require the pool to be drained. When using these sealants, a leak professional should ‘v-cut’ the crack and apply a bead of sealant to the bottom of the ‘v.’ Plaster repair compounds are then used to fill the remainder of the ‘v’ and match the pool surface. This repair method is useful for hairline cracks that are too small to accept a fuller-bodied putty, such as an epoxy.
While surface repairs may be adequate—and certainly cheaper for the customer—a better repair is possible if the entire depth of the crack is filled and sealed with epoxy or urethane. Low-pressure crack injection methods provide this solution and fit the lucrative ‘middle-ground’ option. It gives the customer a lasting repair, but does not involve extensive and expensive concrete modifications.
This method requires the pool to be drained and the surface of each side of the crack to be dry. Special injection ports are adhered to the surface of the pool, over the top of the crack at 300- to 450-mm (12- to 18-in.) intervals. The crack is then covered with the same epoxy to close it and prevent the injected sealant material from draining back into the pool.
Once the surface epoxy has cured, injectable urethane foam is forced into the crack through the injection ports using a special, dual-cartridge gun that maintains a constant pressure of approximately 0.275 MPa (40 psi). The constant pressure and low viscosity of the injection material, before it cures, ensures complete crack penetration.
The foam then expands up to seven times it’s volume, filling not only the crack, but also any voids behind the pool shell. (Injectable epoxy can also be used for this step, however it may require more material and may not completely fill the crack.) After the foam has cured, the ports and surface-seal epoxies are removed using a portable grinding disc. The crack is v-cut and a cosmetic layer of plaster repair compound is used on top.
While low-pressure injection offers the ability to perform permanent repairs, this method can also be adapted to provide some benefit for more serious problems. For example, in situations where future crack expansion is anticipated, the best way to spread this force over a wider area is to install staples or ‘stitches’ across the crack at 200- to 300-mm (8- to 12-in.) intervals.
Staples are made of high-tensile-strength material, such as rebar, stainless steel or carbon fibre. These staples are imbedded into the concrete below the plaster surface with special epoxy before the injection process. The staples and epoxy are covered with the same plaster repair compound used to fill the v-cut of the crack.
Once the pool is drained, a basic 3-4-meter (10- to 15-foot.) crack injection repair can generally be completed in about a half a day. The staple process will add another half day. Pricing is generally based on the job, as this repair will last longer than a simple surface fix.
Another common structural leak, which develops between the skimmer throat and the shell of the pool, can also be fixed with injectable urethane foam. These leaks are often repaired with putty; however, it must be replaced annually. For a permanent solution, the water level should be lowered below the skimmer opening before injecting the expandable foam through a pre-drilled hole in the bottom of the skimmer throat. Any void around the skimmer body is then filled, permanently sealing the leak from the backside. This repair method is more permanent than putty, but less involved than a complete skimmer replacement. It also provides a profitable yet affordable alternative for the leak professional and pool owner.
It is important to keep in mind cracks can indicate a more serious problem. Those who are new to finding and repairing leaks should not hesitate to seek a second opinion from a more experienced builder or structural engineer when faced with a questionable repair. Once familiar with the types of cracks common to a particular area, it will be easier to suggest and deliver effective repair solutions.
Lance Anderson is the owner of Anderson Manufacturing Co., Inc., in St. Paul, Minn. He has been providing leak location and repair solutions to the pool industry for over 20 years. He can be reached at email@example.com.
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