Why fiberglass pools handle Ohio freeze-thaw so well

Water expands by about 9% when it turns to ice, as the Ohio concrete industry's flatwork guidance points out. That expansion is harmless in open air. Trapped inside something, it pushes hard. When water soaks into a porous surface or collects in a crack, freezes, thaws, soaks in a little deeper and freezes again, the damage builds with every cycle.

Northeast Ohio gives it plenty of chances. The National Weather Service in Cleveland lists the average first fall freeze at Akron-Canton as October 19 and the average last spring freeze as April 29. At Youngstown the last freeze averages May 4. In between, the temperature swings above and below freezing again and again, with thaws, rain and refreezes rather than one long deep freeze. That repeated cycling is harder on outdoor materials than steady cold.

The ground moves too. When wet soil freezes near the surface, it can heave upward, then settle as it thaws. Anything rigid set into that soil feels the push.

It flexes. A fiberglass pool is a single molded shell of glass fiber and resin. It is strong, but not brittle. Latham's cold-climate guide describes the shell as flexible enough to accommodate ground movement instead of fighting it. When the soil around it shifts a little with frost, the shell gives a little and comes back, where a rigid structure can crack.

Its surface does not absorb water. The inside of the shell is a gelcoat finish, and Latham describes it as non-porous. Plaster, by contrast, is porous, so water can work into it, freeze and loosen the finish. With no water in the surface, there is nothing to freeze inside it.

It is one piece. A fiberglass shell has no seams in the pool wall for water to find, and no separate liner that can shrink or wrinkle in the cold.

The things freeze-thaw attacks are water trapped inside a material and rigid structures that cannot move. A fiberglass shell offers neither. That is why, in our experience, the winter problems we get called about on fiberglass pools are almost never the pool itself. They are frozen lines, a cracked skimmer lid, a heaved deck panel or a cover that let debris in, all of which come down to installation details and the fall closing.

What surrounds the shell matters as much as the shell. Latham explains that frost heave happens when groundwater in the soil freezes, expands and pushes upward, putting hydrostatic pressure on the pool. Backfilling with crushed stone lets that groundwater drain away instead of sitting against the shell, which reduces the chance of pressure building in the first place.

That is especially important in our soils. The USDA's description of Mahoning silt loam, one of the most widespread soils in the region, notes a perched water table just 6 to 12 inches below the surface from October through June in most years. In plain terms, the ground around many Northeast Ohio pools is wet for most of the cold season. A shell backfilled with native clay would sit in cold, wet mud all winter. A shell set in a draining stone bed has somewhere for that water to go.

Drainage planning and backfill are part of every pool we install, and on wet lots we plan how groundwater will be relieved under and around the shell before we dig.

This is the single most important winter rule for fiberglass. The weight of the water inside the shell holds it down against groundwater pressing up from below. Latham's winterizing guide says never to fully drain a pool, and in most cases to lower the water only about an inch below the skimmer. Drain a fiberglass pool on a wet Ohio lot and the groundwater can push the empty shell up out of position.

Lowering the water just below the skimmer keeps ice out of the skimmer throat while leaving the shell full enough to stay put. If a fiberglass pool ever has to be drained for a repair, that is a job for a professional who can manage groundwater while it is empty.

Fiberglass is not magic. The shell handles freeze-thaw well, but three things around it still need attention.

Plumbing and equipment. Latham notes that pumps, filters, heaters and pipes can be damaged by freezing if they are not winterized. Every line has to be blown out with air and plugged, and the equipment drained. A cracked pipe under the deck is the most expensive winter mistake we see, and it has nothing to do with the pool type.

The deck and coping. The concrete around the pool lives in the same freezing soil and takes the same salt and meltwater as your driveway. Air-entrained concrete, a well-compacted and drained base, and control joints are what keep it flat and intact. Keep rock salt off a new deck its first winter.

Heavy snow on the cover. In the snowbelt around Chardon and Bainbridge, the load on a winter cover can be significant. Keep water pumped off solid covers and follow the cover maker's instructions.

No. A pool holds thousands of gallons, and in a Northeast Ohio winter the water typically forms a sheet of ice on top while the water below stays liquid. That surface ice is why the water level is lowered just below the skimmer. It keeps the ice away from the skimmer opening and the tile or waterline, where expansion could do damage, while leaving the shell full enough to resist groundwater.

Leave surface ice alone. Chipping at it with a shovel or pole risks scratching the gelcoat or tearing the cover, and it will melt on its own. If the cover needs to come off early for some reason, wait for a thaw.

Before opening, take a slow walk around the pool. Check that the water level held through the winter, since a big drop can point to a leak worth investigating. Look over the coping and deck for new cracks, heaved sections or joints that opened up. Once the cover is off, look at the gelcoat for anything new. Then inspect the equipment before it runs: fittings, unions, the filter tank and the heater. Opening is also a good time to replace worn O-rings and check the pump basket lid, so small leaks do not become big ones by July.

Latham's comparison of the three pool types in cold weather rates fiberglass excellent for freeze resistance and very low risk in frost heave conditions when properly installed. It says vinyl liner pools perform well in cold climates with proper winterization, and that their steel and polymer walls stand up well to freezing, but that liners need care to prevent shrinking and wrinkling. It describes concrete as more susceptible, because a rigid, porous structure is exactly what freeze-thaw attacks.

That does not mean concrete pools fail in Ohio. Plenty last for decades. It means they need more from their owners and builders: careful drainage behind the walls, a good finish and diligent winterizing. Our ICF concrete pools add foam insulation on both faces of the wall, which also keeps the concrete away from direct contact with wet, freezing soil.

Yes. Frost depth in Ohio is set locally. The Ohio Residential Code requires footings to extend below the frost line listed for the jurisdiction, and Northeast Ohio values are deeper than those in the southern part of the state. Anything with a footing near the pool, like a pergola post, a retaining wall or a seat wall, has to respect that depth. We plan those details in the 3D design so the pool, the deck and every structure around it are built for the same winter.

We also think about where snow will go. Shoveled or plowed snow piled against a pool fence or on the deck edge melts and refreezes all winter. Leaving a spot for it in the layout is a small detail that saves the coping.

If you want the pool type that asks the least of you through an Ohio winter, fiberglass is the strongest choice, and it is a big part of why we lead with it. Our packages use Liberty Composites shells and run from $68,400 to $103,900 installed, including a 4 ft concrete deck and Pentair equipment. Build it on a draining base, keep it full, close it properly each fall, and it will come out of March looking the way it went into October.

If you would rather hand winter off entirely, we also offer fall closings and spring openings as part of our pool service.