A crack in your pool surface is one of those things that’s easy to put off. It’s small. The pool is still holding water. You’ll get to it before next season. And then next season comes around and the crack is wider, the plaster around it has started to flake, and what would have been a straightforward repair is now a bigger conversation.
That pattern happens constantly with pool cracks — particularly here in East Tennessee where the freeze-thaw cycles we get through winter do exactly what you’d expect to concrete and plaster that’s holding water. A crack that’s ignored from October to April has had six months of ice expansion working against it.
Here’s what you need to know about pool cracks — what type you’re dealing with, what caused it, how repairs actually work, and when a surface patch is the right move versus when you need a professional to take a look.
Before anything else, you need to identify what kind of crack you’re looking at. The approach, the urgency, and the cost are completely different depending on whether you’re dealing with a surface crack or a structural one. Treating a structural crack like a surface patch is one of the more expensive mistakes a pool owner can make — around 50% of standard epoxy crack repairs fail within two years precisely because the repair addressed the symptom without addressing what’s actually happening beneath the surface.
Surface cracks are shallow fractures that affect the plaster or finish layer but don’t penetrate the pool shell. They’re thin — often called hairline cracks — and sometimes appear in a web-like pattern called spider cracking. This is common in older plaster finishes and on pool steps where the surface gets the most wear and foot traffic.
Surface cracks are primarily a cosmetic issue. They don’t affect the structural integrity of the pool and they don’t cause leaks by themselves — though they can allow moisture to work deeper into the concrete over time if left unaddressed, which is why monitoring and sealing them matters. They’re also the type of crack that pool owners can often repair themselves with the right materials.
Structural cracks go deeper than the finish layer. They penetrate through the gunite, concrete, or fiberglass shell of the pool itself. These are wider than hairline cracks, often run along the walls or floor rather than just across the surface, and may be visibly stepped or offset on one side. The most telling sign of a structural crack is water loss — if your pool is consistently dropping water levels and you’ve ruled out evaporation and equipment issues, a structural crack is a likely cause.
Structural cracks don’t happen randomly. They’re caused by something — soil movement, hydrostatic pressure from groundwater, freeze-thaw damage, or an original construction issue — and that cause doesn’t go away just because you fill the crack. A surface patch on a structural crack is a temporary measure at best. The crack will reappear, usually wider and sooner than expected.
An active crack is one that’s still moving. If you mark the ends of a crack with a pencil and come back a week later to find it’s grown or shifted, you have an active crack. This means whatever is stressing the pool structure is still happening. Active cracks should not be repaired with standard patching — they need a professional assessment to understand what’s driving the movement before any repair work begins.
This is the big one for pool owners in our part of the state. When water gets into concrete or plaster and then freezes, it expands by about 9% of its original volume. That expansion creates internal pressure that cracks the surrounding material from the inside out. A pool that isn’t properly winterized — with standing water in cracks, in pipes, or in equipment — is vulnerable to this cycle every winter. It’s not dramatic damage all at once. It’s incremental, season after season, until the small surface crack that was there last spring is suddenly a wide fracture running across the pool floor.
Soil that wasn’t properly compacted before pool installation, soil with high clay content that swells when wet and shrinks when dry, and soil affected by nearby tree roots or poor drainage — all of these create movement that pools aren’t built to handle. When the ground shifts, the pool shell shifts with it. The result is structural cracking, typically along the walls or at corners where stress concentrates.
When the water table rises — after heavy rain, for example — the pressure of groundwater pushing against the outside of the pool shell can exceed the water pressure inside. This pushes against the walls and floor from the outside, causing cracks or in severe cases causing the pool shell to pop up from the ground entirely. Hydrostatic relief plugs installed in the pool floor exist specifically to equalize this pressure — but if they’re blocked, failed, or weren’t installed correctly, the pressure has nowhere to go.
Plaster has a lifespan. Most pool plaster surfaces last 10 to 15 years before they need resurfacing. As plaster ages it becomes more brittle and more prone to surface cracking, especially under the stress of temperature changes. If your pool was plastered more than a decade ago and you’re seeing widespread hairline cracking across the surface, the plaster itself may have reached the end of its useful life rather than there being a specific cause to diagnose.
Rebar that wasn’t properly tied during construction, concrete that wasn’t kept moist enough during the curing process, or gunite that was applied unevenly — all of these construction deficiencies can result in cracking years later. If your pool has always cracked more than expected and in unusual places, the original construction is worth looking at.
Surface crack repairs fall into two categories depending on whether you can do them with the pool full or whether the pool needs to be drained. Minor hairline cracks in the floor or walls that aren’t causing any water loss can often be addressed underwater without draining. Larger surface cracks or those in the plaster that require grinding and replastering need the pool emptied first.
For small, shallow hairline cracks, the basic process is straightforward. Widen the crack slightly with a flathead screwdriver to remove any loose material and create a surface the repair material can bond to. Use a stiff brush to scrub out any algae, dirt, or oils from the crack — the cleaner the bonding surface, the longer the repair holds. Mix pool putty or apply an underwater epoxy repair compound and press it firmly into the crack, smoothing flush with the surrounding surface.
Products specifically designed for underwater pool crack repair — pool putty, hydraulic cement, or underwater epoxy formulations like Aquaguard 5000 — are what you want here. Standard concrete patch products and exterior sealants are not designed for constant water exposure and will fail quickly. Use materials made specifically for pools.
For larger surface cracks or those in plaster that need proper color matching and a lasting repair, the pool needs to be drained. A few important notes before you drain. Don’t drain after heavy rain — the saturated ground creates hydrostatic pressure that can damage or even lift an empty pool shell. Remove your hydrostatic relief plugs from the pool floor once drained to allow groundwater pressure to equalize. And drain carefully and slowly — a pool that empties too fast can crack further from the sudden pressure change.
Once drained and dry, use a 4-inch grinder to widen the crack into a V-shape. This creates more surface area for the repair material to grip. Clean thoroughly. Apply a bonding additive to the crack surfaces before filling — this significantly improves adhesion of the plaster or hydraulic cement to the existing material. Fill with hydraulic cement for deeper cracks and finish with a pool plaster mix that matches your existing surface as closely as possible. Keep the repaired area moist while it cures — a wet towel or plastic sheeting over the patch, with water applied twice daily, prevents the plaster from drying too quickly and cracking again.
Fiberglass pool repairs work differently than plaster or gunite. Sand the cracked area to remove sharp edges and create a mechanical bond surface. Clean thoroughly with acetone to remove any oils or contaminants. Apply fiberglass gel coat — matched to your pool’s color as closely as possible — over the crack using a putty knife and work it into any voids. Once fully cured, sand lightly for a smooth, flush finish. Fiberglass repair requires gel coat that matches your pool’s specific color and age — the older the pool, the more faded the original finish, which makes color matching a challenge. A professional with experience in fiberglass pool repair will get a better color match than most homeowners attempting it for the first time.
Vinyl liner cracks and tears are patched differently from concrete or fiberglass. Minor liner damage can be repaired underwater without draining using a vinyl patch kit. Cut the patch in an oval or circular shape — sharp corners tend to peel — at least half an inch larger than the damage on all sides. Apply vinyl adhesive to the patch, fold it briefly, then unfold and apply it firmly over the damage, pressing out any air bubbles. Hold it in place for several minutes. The repair should be watertight within 24 hours. For larger liner damage or liner that has become brittle and is cracking in multiple places, full liner replacement is usually more cost-effective than continued patching.
Structural cracks need professional repair. This isn’t a liability disclaimer — it’s a practical reality. The tools required, the techniques involved, and the judgment calls that need to be made during the repair are not something that translates well to a first-time attempt. Getting it wrong means doing it twice, and structural crack repairs that fail leave you with a worse situation than what you started with.
Steel or carbon fiber staples are the most reliable long-term repair for structural cracks in concrete and gunite pools. The process involves cutting horizontal slots across the crack at regular intervals, drilling holes at each end of the slot, and installing staples that bridge both sides of the crack and lock it mechanically. This stops the crack from widening further and distributes the structural load across both sides.
Carbon fiber staples — a newer alternative to the traditional steel rebar approach — are thinner, non-corrosive, and easier to install flush with the surface. They’re the current standard in quality structural pool crack repair.
Epoxy injection is often used alongside staples. Injection ports are installed along the crack, sealed in place, and the crack is flushed before expanding epoxy foam is injected under pressure to completely fill the void. Once cured, the ports are ground flush. The combination of mechanical stabilization from staples and complete void filling from epoxy injection is the most durable repair approach for structural cracks.
If a pool has multiple cracks — surface and structural, scattered across the walls and floor — or if the plaster is significantly aged, patching individual cracks often makes less sense than resurfacing the entire pool. A full resurfacing strips the existing finish and applies new plaster, quartz aggregate, or pebble coating across the entire surface. Done correctly, a resurfaced pool looks new and the new surface lasts 10 to 15 years. The cost is higher than patching, but the result is comprehensive rather than a patchwork of repairs that will keep multiplying.
Some cracks can wait for a scheduled repair appointment. Others should be addressed quickly. Pay attention if you see any of the following.
Water loss that exceeds normal evaporation. In Tennessee’s summer heat, a pool can lose about a quarter inch of water per day to evaporation. More than that consistently — especially if you notice wet ground around the pool or near your equipment pad — suggests a leak at a crack location.
A crack that is visibly widening or growing in length. Mark the ends with a grease pencil and check it weekly. Active cracks need professional assessment before any repair attempt.
Cracks along the waterline tile or in the bond beam — the structural band around the top of the pool. These are often signs of ground movement or freeze-thaw damage and shouldn’t be addressed with surface putty alone.
Cracks on the pool floor that feel soft or spongy underfoot. This suggests the concrete beneath the crack has been compromised, which is a structural issue requiring professional evaluation.
Multiple cracks appearing in a short period of time, particularly after a hard winter or a period of heavy rain. A pattern of new cracking suggests an ongoing structural stress that needs to be identified and addressed, not just patched.
Proper winterization is the single most important thing a pool owner in this climate can do to prevent crack damage. That means getting water out of pipes and equipment, lowering the water level to the right point, covering the pool properly, and addressing any existing cracks before temperatures drop. A small surface crack going into winter is a bigger surface crack coming out of spring.
Keeping pool chemistry balanced also matters more than most people realize. Water that’s too acidic etches and weakens plaster over time. Water that’s too basic causes scaling. Either extreme accelerates the surface deterioration that leads to cracking.
Annual inspections are worth it. Having someone who knows what to look for walk the pool before the season starts catches problems when they’re small and inexpensive rather than when they’ve been developing undetected for a full year.
If your pool has cracks you’re not sure about — whether they’re surface-level cosmetic issues or something that needs a closer look — the honest answer is that it’s worth getting an expert opinion before you decide how to handle it. A crack that looks minor from above can tell a different story once someone familiar with pool structure takes a proper look at it.
At Spas and More, we handle pool crack repair and resurfacing across East Tennessee. If your pool needs attention before the season starts, give us a call and we’ll take a look and tell you straight what it needs.
(423) 337-1859
spasandmore.net
815 County Road 188, Niota, TN 37826
Serving Niota, Athens, Etowah, Cleveland, Sweetwater, Madisonville and surrounding communities across East Tennessee
