Fiberglass Pool Repair

fiberglass swimming pool before resurfacing

How to Empty a Fiberglass Swimming Pool

Underground Water is a Pool's Worst Enemy

Never empty a fiberglass pool during the rainy season. If you have standing ground water hours after it rains anytime during the year, there is a strong possibility that the pool will lift. In my 11 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. The writer assumes no liability for any damages to any swimming pool.

Empty the Swimming Pool

There are two standard methods to empty a pool

  • If you have a sand filter, buy a backwash hose at your local pool supply store and attach it to the valve on the filter.

  • If you do not have a sand filter, then use a submersible pump (sump pump).

If using a backwash hose, keep a sump handy to remove the last 6" or so of water. It is imperative to remove these last few inches of water immediately so the bottom drain cover can be removed. This only applies to a center bottom drain which may have a relief valve. There is no relief valve in a wall mounted bottom drain, so the timing isn't relevant.

Relief Valves

Hydrostatic Relief Valve It is probably located under the bottom drain cover, and it is probably stuck after all these years.

After using a sump to remove the last six inches or so of water, pry (or unscrew) the drain cover off with a screw driver and look inside. If there are two pipes going out, you do have a hydrostatic relief valve. One pipe goes to the pump, and the other goes underneath the pool about two feet and ends.

Just a few inches inside one of the pipes is the stuck valve. Gently (at least at first) tap the valve with the handle of a screwdriver. The underground water should begin to flow immediately.

Relief Valve Follow the above directions and look inside the drain. There will be one pipe going to the pump, and a removable valve secured with two screws. Take out the valve which releases the underground water.

Relief Drain Plug Some fiberglass pools have a bottom drain plug with no attached plumbing. Just unscrew the plug as soon as possible to enable the underground water to flow into the pool. If there is no flow of water, there is no reason for concern, at least for the time being.

Stand Pipe

Some pools had a water problem during construction and, to the current owners good fortune, have a "stand-pipe" located near the pool. If this is the case, simply remove the cap and place a long pliable hose into the pipe, then attach the hose to a utility pump and drain the underground water. This pvc pipe goes directly into a french drain under the pool. A french drain under the pool is usually 4' x 4' x 2' deep, and filled with stones (size of drain and stones can vary).

The purpose of a stand pipe is to drain the water that is under the pool. This ground water is your pool's worst enemy. It can do serious damage to your swimming pool when the pool water level is too low. Never let anyone empty your swimming pool, including a pool professional, without first having a discussion about the stand pipe and the hydrostatic relief valve. Never permit anyone to empty a fiberglass swimming pool unless they can describe both these items.

Well Points

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.

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Fiberglass Pool Repair
Warminster, PA

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