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
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
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
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.