Don’t drain your gunite pool before reading this

Why an empty gunite pool can float

A gunite shell full of water is heavy enough to stay put. Empty, it’s a concrete boat. When the soil around the pool is saturated, groundwater pushes up on the bottom of the shell the same way lake water pushes up on a hull. The water inside the pool is the ballast that holds it down. Take that ballast out while the ground is wet and the shell can lift, sometimes an inch, sometimes several feet on one end.

Pool guys call it popping. Once a shell pops, it never sits right again. The plumbing shears off at the wall, the deck cracks where the coping tore loose, and the shell itself usually cracks from the twisting. We’ve seen a pool popped by a weekend acid wash turn into a bigger bill than a full resurfacing job would have been. Some popped shells can’t be saved at all.

Jackson soil and rain stack the deck against you

Two local facts make popping more likely here than in most of the country. First, the soil. Much of the metro sits on Yazoo clay, an expansive soil documented by the Mississippi Department of Environmental Quality’s Office of Geology. That clay swells when wet and drains slowly, so rainwater perches around a pool shell for weeks instead of soaking away. Second, the rain itself. Jackson averages roughly 55 inches of rain a year, per the National Weather Service office in Jackson, which is more than Seattle gets. From December through April the ground here rarely dries out.

Put those together and a pool drained in March in Belhaven or Madison is sitting empty in a bathtub of wet clay. That’s the pop scenario.

When a pool actually needs to be drained

There are only a few good reasons to empty a gunite pool:

• Replastering or resurfacing. The finish can’t be applied underwater. This is the most common reason and the one where timing matters most. More on what that work involves is on our resurfacing page.
• Major structural repair. Cracks below the waterline need a dry shell for injection and staples.
• A true drain and clean. A pool that sat black for years sometimes costs less to drain and pressure wash than to chemically recover.
• Water chemistry that can’t be corrected. Stabilizer or calcium so high that dilution is the only fix.

What does not require draining: finding a leak. Dye testing, pressure testing, and acoustic location all happen with the pool full. If someone tells you the pool has to be emptied to find a leak, get a second opinion. Ours is on the leak detection page.

How we drain a shell without popping it

When a repair does call for an empty pool, the job is managing groundwater, and it starts before the pump does.

1. Check the water table first. We sound the skimmer standpipe or an existing well point to see where groundwater is sitting. High water table means we wait or dewater. Guessing is how pools pop.
2. Open the hydrostatic relief valves. Most gunite pools have relief plugs in the main drain pot. Opened, they let groundwater flow up into the empty pool instead of lifting it. On older metro pools those valves are often plastered over or seized, so we locate and free them before draining. If a pool has none, we can install them during the work.
3. Pick the season. Late summer through fall is the safe window around Jackson. The clay is at its driest and the water table at its lowest. An August drain is a different risk than a February one.
4. Keep the empty window short. Days, not weeks. We schedule the drain so the repair crew starts the next morning, and we refill as soon as the new finish allows. An empty shell waiting on a delayed contractor is exposure with no payoff.
5. Watch the weather. A tropical system dumping six inches on an empty shell changes the math fast. If heavy rain is coming, we’d rather postpone than gamble with your pool.

If your pool already popped or cracked

The signs are hard to miss: one end of the coping sits proud of the deck, doors on the skimmer lid don’t line up anymore, or a fresh diagonal crack showed up after the pool was emptied. A popped shell isn’t always a total loss. If the lift was small, the plumbing can be repaired, the shell stabilized, and cracks injected. That work is covered on our crack repair page, and typical prices for all of it are published on the cost guide.

The honest summary: draining a gunite pool around Jackson is a routine step in a repair when it’s planned, and an expensive mistake when it’s casual. If your pool needs work that calls for a drain, have someone do it who checks the groundwater before pulling the plug.