If you own a vinyl liner swimming pool in the Tidewater area, you have probably heard of or experienced firsthand the phenomenon pictured above-- a floating liner. The severity of damage from these events is determined by the age and fitness of the liner, history of prior events, volume of water intrusion, action taken during and after the event, and elapsed time after event before repairs commence. There are different causes of this phenomenon, but in most cases the cause is local rainwater runoff from property features such as the home and adjacent hardscaping.
Not all instances of a floating liner feature this air bubble. For the air bubble to occur, the intruding water must originate well above the "cove" area and usually above the pool water level. For instance, if the intruding water source is a broken buried pipe or leaking liner, the air being displaced by the intruding water will simple rise along the wall panel and eventually to the atmosphere. This is not possible when the source of intruding water is above the pool water level because the water forms a kind of seal between the wall panel liner, effectively trapping the air.
In a very few instances, an air bubble is never witnessed when the intruding water is due to rainwater runoff. In these instances, we usually find that the liner is at least five years old and was manufactured with the least undersize. The closer the liner fit is to the underlying pool structure, the less air will be present to coalesce. Also, as liners age they continue stretching and conforming to the underlying pool structure which further reduces the amount of air available to coalesce.
In Tidewater, except pools built on property exposed to tidal flow, floating liners are almost never due to true groundwater. If there were so much local groundwater present to float a liner, the construction process would have required 25-50 well points just to carry out the excavation. The cost of installing these well points and operating the pumping equipment would likely be more than the cost of the pool alone, making such a scenario highly unlikely.
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Most cases we encounter are simple cases of rainwater runoff and nonexistent drainage. During even minor rain events, runoff from nearby structures such as the house, shed, garage, and poolhouse is not captured at the base of gutter spout and simply dumped onto the turf or hardscaping. This runoff combined with the turf's and or hardscaping's runoff seeks the lowest point on the site which unfortunately for pool owners is found underneath the pool's hardscaping, particularly concrete decks. These decks are usually poured over soil which continues to settle and compact after the pool construction is complete, and this continued compaction creates a void between this soil and the bottom of the concrete deck. The local runoff invariably travels downhill to this void by soil percolation, tunnels, and other natural means, creating a reservoir around the perimeter of the pool.
This reservoir of water is not yet done travelling. Gravity constantly forces the water down and it finds more empty space around the base of the pool walls. Because vinyl liners are designed stretch-to-fit and manufactured undersize, many small radius corners and sharp 90* features of the pool contain areas of air behind the vinyl liner. Colloquially known as "the cove," a large portion of air can be found at the 90* intersection of the vertical wall base and shallow-end floor. As gravity forces the reservoir of water down toward this cove, the air does not percolate up through the densely compacted soil. Instead, the air coalesces in the building reservoir of water--now forming around the perimeter of the entire shallow-end--forming a single large bubble. The large bubble in the above photo is not a bubble of water! Indeed it is a bubble of air, sandwiched between the vinyl liner membrane above it and the standing water below.
We offer two solutions to rectify the problem of floating liners. The lowest cost solution is to capture all rainwater from gutters, and carefully construct a system of french drains around the pool and backyard. In the most difficult cases, a drainage system must be constructed in the pool and under the liner. This system is then connected to a 12" cased sump located away from the pool and an automatic pump is permanently installed in this sump. These systems provide the forced drainage required when the pool and turf elevations prevent the use of french drains.