Vinyl pool liners are protected by special additives and coatings that can withstand extremes of sun, temperature and constant exposure to chemically treated water. However, even the highest quality vinyl liner is subject to staining, wrinkling, shrinking or discoloration if the pool water is not balanced and treated correctly.
This type of damage to the liner is often associated with common missteps in maintenance. Here, we look at the signs and solutions to four different problem areas in maintaining vinyl liners.
The addition of a single chemical can damage a pool liner if the substance is not circulated sufficiently. Chemicals such as chlorine can settle in the deep end of the pool and bleach the liner if they are not allowed to circulate for several hours before a pool is closed for the season.
Spot bleaching of vinyl liners can also occur if undissolved particles of calcium hypochlorite or other slow-dissolving sanitizers are allowed to settle on the bottom of the pool. This can be prevented by pre-dissolving sanitizers in a bucket of pool water and adding the solution by pouring it through a sieve.
Using large, single doses of hydrochloric (muriatic) acid to adjust pH or total alkalinity levels can also damage liners. The acid then can chemically attack the liner’s printed pattern, since it is not sufficiently blended with pool water.
When a pool is closed for the season, professionals should install a winter cover that tightly seals around the perimeter. This will prevent the accumulation of leaves and insects during the winter months. This organic debris left on vinyl surfaces can cause staining and bleaching, and fungi that produces a pink stain on the vinyl.
Printed vinyl liners with base colors such as white, turquoise, light blue, grey and dark royal blue have excellent resistance to chlorine bleaching. Medium blue vinyl liners are, however, more susceptible to bleaching or loss of color if exposed to high concentrations of trichloroisocyanurate stabilized chlorine. This can happen in a period as short as 6 to 24 hours.
The immediate effects of other types of chlorine such as dichloroisocyanurate, calcium hypochlorite and sodium hypochlorite (liquid chlorine) are not as rapid or severe, as long as they are not mixed with other chemicals during or shortly after being added to the pool. Solutions of these types of chlorines can be applied directly to the liner for several hours to bleach out stains without adversely affecting the vinyl. If the concentrations of these types of chlorine are allowed to remain higher than the recommended levels of 5 ppm for superchlorination or 10 ppm for shocking for long periods of time, gradual bleaching of most blue liners will occur.
Be aware that certain combinations of pool chemicals at high concentrations can cause bleaching of vinyl liners.
Sticky substances, often referred to as “pool tar” or “pool goo,” can adhere and coat part of vinyl pool liners. This is sometimes caused by the interaction of quaternary ammonium compounds (quats) used in some algaecides and decaying organic material such as leaves, grass and insects.
Even chlorine can interact with quats to form a sticky material if both the chlorine and algaecide exceed the recommended levels. Quats can easily come into contact with high chlorine levels in automatic chlorinators, resulting in a gummy material being gradually fed into the pool, where it eventually precipitates on the liner.
Gummy material from the chlorinator can form when organic materials from cosmetics or tanning lotions are oxidized by high chlorine concentrations, resulting in a beige waxy substance.
Although it is not harmful to swimmers, sometimes a light coating of vinyl plasticizer material, which turns dark when contaminated with dirt, may rise to the surface of newly installed liners during the first idle period of winterization. This phenomenon is attributed to a lack of circulation, as it has never been observed in a pool that has been circulated over the winter. The material will almost always reabsorb in two to three weeks if the water is allowed to warm up (to over 21° C / 70°F) and circulate before being shocked with chlorine (at 6.0 ppm to 8.0 ppm) every other day.
Wrinkling and stretching
Vinyl increases dimensionally as it absorbs water, and wrinkles can develop even in properly-sized liners. The cause of this excessive water absorption is believed to be high levels of chlorine or bromine. If the sanitizer level is allowed to remain high, as much as five times the normal amount of water can be absorbed, which makes controlling water chemistry essential to maintaining the integrity of the liner.
Immersion testing of liner samples on chlorinated and brominated water in the 20 ppm to 50 ppm range shows that weight gains continue to climb indefinitely without leveling off, causing the size of the liner to increase by 1- to 3 percent.
To avoid stretching and wrinkling in vinyl liners, chlorine levels should not be allowed to remain higher than 3 ppm for an extended period, while bromine levels should not be allowed to exceed a maximum of 4 ppm.
Although peak chlorine levels of 5 ppm to 10 ppm are required for superchlorination, they should be allowed to return to the 2-3 ppm range by natural dissipation.
Controlling pH levels is also important in preventing wrinkling because pH affects sanitizer activity. A low pH of less than 7.0, for example, can cause a vinyl liner to discolor, wrinkle, stretch, lose tensile strength and increase in weight. A high pH level above 7.6 can lead to scaling or staining of the liner.
The information in this article is based on the strength of high quality, 100 percent virgin vinyl sheeting. Installers should always be aware of the quality of the vinyl being used in the pool liners they purchase, install and service.