Why liners wrinkle and how to avoid it

The three main causes

Water chemistry

PVC absorbs a little water. When the pH stays low or the chlorine high for a long time, the material absorbs more, softens and grows slightly. The extra surface has nowhere to go and forms ripples, usually on the floor and in the corners. Prevention means stable chemistry: pH 7.2–7.6, free chlorine 1–3 mg/l, and never chlorine granules directly on the liner, because they create a very high local concentration.

Groundwater

On plots with a high water table, near streams or after heavy rain, groundwater can push on the membrane from below. While the pool is full, the weight of the water holds it in place. But if the level drops a lot, the membrane can lift and, when the pool is refilled, not settle back as before. This is already considered at the excavation stage, where drainage is provided when the ground requires it.

Draining

Without water, the liner is exposed to sun and air; it dries out, shrinks and loses the pressure that keeps it taut against the walls. This is the most common cause of permanent wrinkles, and of tears too. That is why a liner pool is never fully drained; the water is renewed gradually, as we explain in why we don't drain a liner pool.

What a reinforced membrane changes

Simple, unreinforced liners that hang from the edge are the most prone to wrinkles, because they are elastic and have nothing to hold their dimensions. A reinforced membrane has an internal fibre mesh that keeps its shape stable, and it is welded in place, so it swells much less. It is not invulnerable, though: years of out-of-range chemistry, an uneven floor or water under the pool can still create local ripples.

Prevention, in order

1. Test pH and chlorine at least once a week, and more often in hot weather.
2. Dissolve granular chlorine in a bucket before adding it; put tablets in a feeder or a free-floating dispenser, not on the floor.
3. Don't lower the water level more than necessary. In winter, just below the skimmers is enough, as described in winterizing your pool.
4. If the plot has groundwater, discuss it before construction so that drainage can be planned.
5. After very heavy or prolonged rain, check the floor for any lifting.

If wrinkles appear

Start with the chemistry: test, correct the pH and chlorine, and watch for a few weeks to see whether the wrinkle stays the same. Don't try to flatten it with sharp tools, and don't drain the pool to fix it, because you will make it worse.

A small, shallow wrinkle does not threaten watertightness as long as the membrane is intact, but the fold gets rubbed by feet and the vacuum and wears faster. If the wrinkles grow, appear suddenly after rain, or come with a drop in water level, ask a technician to check: there may be water under the membrane or a leak.

Questions

See also