by Bill Nash
*How to Empty a
Gunite, or Concrete Swimming Pool Guide
Every swimming pool built or
manufactured must, at one time or another, be emptied
for repair or resurfacing. There is no such thing as a
pool that will never need to be drained, regardless of
what you may have been led to believe.
With this in mind, almost every
type pool listed above has some method of relieving
the underground water pressure. This is a safety
feature built into pools to prevent the hydrostatic
pressure caused by underground water from damaging the
swimming pool. We are talking about serious damage, so
please take heed to the precautions I've listed.
Because fiberglass pools weigh
the least, as compared to concrete or gunite, the
danger of lifting is greater.
In my 15
years in this industry, I’ve never had a fiberglass
pool lift, however two gunite pools did "pop". So the
possibility certainly exists. Use this information as
a guide in an effort to prevent this problem.
Never empty a fiberglass pool during the rainy season
unless the pool has a built-in system for relieving
the underground water pressure (which most do). If you
have standing ground water hours after it rains
anytime during the year, there is a strong possibility
that any pool (gunite or fiberglass) will lift.
Hydrostatic Relief Valves
If your concrete or gunite pool has hydrostatic relief valves
(usually located near the bottom of the steep slope), remove
them as soon as you can get to them while emptying the
pool. If you have an operating bottom drain, remove
the cover and see if it has a hydrostatic relief valve
(almost all do),
unscrew and remove the valve as
pool is drained.
The last foot or so of water probably won't drain out,
so be ready with a sump pump to immediately place at
the drain to remove the remaining water. This is
extremely important, and must be done quickly, so the
bottom drain can be accessed for removal of the cover.
After opening the valve, place a pipe into the valve
(about 3’ to 6’ long) and put a hose through the pipe,
Bring the hose up over the
top of the coping and attach a pump to draw the
water from under the pool. This is just ground water,
so there is no chemical content to be concerned about.
Point the water flow to a drainage area away from the
Some pools had a
water problem during construction and, to the current
owners good fortune, have an inconspicuous "stand-pipe"
located 10' or 30' from the pool. The pipe is less than
a foot high and may or may not have a cap, place a long
hose into the pipe, then attach the hose to a utility pump and drain the underground water.
Some are located under the diving board and some can
also be located near the pump and filter.
Quite often, a stand
pipe equivalent was used when the pool was built, and a
high water table was encountered. You may have a piece
of black or white PVC emerging from the ground on the side of the deck
next to the grass. It should be slightly lower than the
top of the deck and usually goes unnoticed. This PVC goes directly into a 4' by 4'
pit filled with stone. This PVC serves the same function
as a stand-pipe, and should be used as explained above.
If you’re in a beach area or other low lying area, you
may need to consider “well points”, but this is a last
resort and is rarely necessary under other conditions.
When well points are necessary, they should be
installed by an experienced individual. Some pools
require well points only on one side, while others
must have well points around the entire pool.
*This article may be reprinted
in its entirety with no omissions and with full credit to the Author.
607 Louis Drive Suite I
Warminster, PA 18974
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