How to Fix Cracks in Your Inground Pool And Keep Them Gone

Reviewed by a Certified Pool Technician (CPT)

---

The Short Answer

Most inground pool cracks are cosmetic and can be repaired with underwater plaster or epoxy without draining the pool. Structural cracks those that are wide, growing, branching, or accompanied by water loss require more extensive repairs and sometimes professional evaluation before attempting a DIY fix. Before repairing any crack, determine its severity, check for leaks, address the underlying cause, and use the appropriate repair method to prevent the problem from returning.

---

Discovering a crack in your pool surface is one of those moments that sends pool owners straight to worst-case thinking. Underground leaks. Compromised structure. A very expensive problem. The reality is more reassuring: the vast majority of inground pool cracks are surface-level and cosmetic the result of normal aging, temperature cycling, or minor ground movement. They're common, they're fixable, and most can be repaired without draining the pool.

But some cracks do indicate structural problems, and confusing the two is where things go wrong. The difference between a hairline crack that needs a $20 plaster patch and a structural fracture that needs a professional assessment is worth knowing before you reach for a trowel.

Cosmetic vs. Structural Pool Cracks: How to Tell the Difference

This is the most important assessment you'll make, and it determines everything that follows.

Cosmetic (Surface) Cracks

Cosmetic cracks affect only the plaster, pebble-tec, or tile surface of the pool and don't penetrate to the shell (the gunite, shotcrete, or concrete structure underneath). They're the most common type of pool crack, especially in pools more than 10 years old and represent normal surface aging rather than structural failure.

Characteristics of cosmetic cracks:

• Thin, hairline width (typically less than 1/16 inch)

• Shallow depth, you can't feel significant depth with a fingernail

• Found in a single direction or small isolated area

• Pool water level is stable (no unexplained water loss)

• No corresponding staining, moisture, or wet soil outside the pool

• No visible movement or change over short observation periods

Best repair approach: Underwater epoxy putty or pool plaster (with pool full) for minor cracks; plaster repair with a drained pool for longer or wider surface cracks.

Structural Cracks

Structural cracks penetrate through the pool's surface layer and into the shell itself. These are less common but significantly more serious they can cause leaks, compromise the pool's integrity, and require more than a surface patch.

Characteristics of structural cracks:

• Width of 1/4 inch or more, or any crack that is visibly widening over time

• Deep enough to see the shell material beneath the plaster

• Branching or "spider web" pattern radiating from a central point

• Accompanied by unexplained water loss (pool level dropping faster than normal evaporation accounts for)

• Accompanied by ground movement, soil settling, or sinkholes near the pool

• Offset on either side of the crack (one side higher than the other) — indicates structural movement

• Multiple cracks appearing in a short period

Per APSP/PHTA guidance on structural pool safety: structural cracks should be professionally assessed before repair attempts are made. A professional can determine whether the crack is stable (not actively moving) or progressive (growing), whether water is actively leaking through it, and whether the underlying structure requires stabilization before a surface repair can hold.

Check for Leaks Before You Repair

Before doing any repair work, determine whether the crack is leaking. A cosmetic crack that looks minor may still be losing water; a crack that appears serious may be stable and dry.

The Bucket Test

The bucket test is the standard DIY method for detecting pool leaks:

1. Fill a 5-gallon bucket with pool water and place it on a pool step (so it's at the same temperature as the pool water)

2. Mark the water level inside the bucket with tape

3. Mark the pool's water level on the wall

4. Wait 24 hours without using the pool, running the pump, or adding water

5. Compare: if the pool water level dropped more than the bucket, you likely have a leak

Normal evaporation affects both the bucket and the pool equally. If the pool drops significantly more than the bucket, the excess is likely coming from a leak.

Dye Testing

For a more targeted leak assessment once you've confirmed water loss, dye testing near the crack can confirm whether the crack is the source:

1. Turn off the pump and let the water go still

2. Using a pool leak dye (or food coloring as a substitute), carefully apply a drop near the crack

3. Watch: if the dye is drawn toward and into the crack, water is actively moving through it

If dye testing confirms the crack is leaking, it changes your repair approach; a surface patch alone won't hold long-term on an actively leaking structural crack. Consult a professional before proceeding.

First, Assess the Damage And Know When to Drain

Once you've characterized the crack type and confirmed whether it's leaking, you can decide on your repair approach:

Repair without draining is appropriate for:

• Thin, hairline cosmetic cracks

• Cracks that aren't leaking

• Isolated small spots where plaster has roughened but not come loose

Drain the pool for repairs when:

• The crack is longer than a few inches or wider than 1/16 inch

• Plaster is loose, bubbling, or coming off in chunks

• You need to clean and fully expose the crack for a lasting repair

Important warning if draining with existing cracks: A drained pool with existing structural weakness is at increased risk of "pool pop-up" hydrostatic pressure pushing the empty shell upward from the ground. This is rare but genuinely catastrophic when it happens. Before draining a pool with significant cracking, check with a pool professional about local groundwater conditions and hydrostatic valve status. Never drain a pool after heavy rainfall or in areas with high water tables without professional guidance.

Repair Method 1: Underwater Plaster (Pool Full)

Best for: Minor cosmetic hairline cracks; pool owners who want to avoid the cost and hassle of draining.

What you'll need:

• Swimming goggles

• Underwater pool plaster or epoxy putty (formulated to cure underwater)

• Paint scraper or putty knife

• Wire brush

Steps:

1. Mix the underwater plaster or epoxy according to manufacturer's instructions and roll into a ball or working amount.

2. Put on goggles and enter the pool. No need to turn off the pump; circulation won't significantly affect this repair.

3. Using the pointed end of the paint scraper or putty knife, rake along the crack to fully expose it. Use the wire brush to remove any algae, calcium deposits, or debris from inside the crack.

4. Press the plaster or epoxy into the crack firmly, using the putty knife or scraper to push it fully into the void.

5. Smooth the edges flat against the pool surface. Feather the edges so there's no raised ridge.

6. Allow to cure per manufacturer's instructions before heavy use of that area.

Limitation: Underwater repairs work well for surface-level cosmetic cracks. They won't provide a long-term fix for structural cracks with active movement or leaking.

Repair Method 2: Plaster Repair with a Drained Pool

Best for: Longer or wider cosmetic cracks where a more thorough, lasting repair is needed.

What you'll need:

• Safety goggles, ear protection, heavy-duty work gloves, closed-toe shoes

• Grinder or masonry saw

• Soft-tipped (painter's) brush

• Underwater sealer

• Pool plaster

• Grouting sponge

• Putty knife or trowel

Steps:

1. Safety first. Full PPE before picking up any tool.

2. Using the grinder or masonry saw, cut along the crack approximately 1/2 inch on each side and 1/2 inch deep. Cut diagonally toward the crack to create a dovetail shape, this gives the new plaster a mechanical grip. Extend the cut 1 inch beyond each end of the visible crack.

3. Remove the cut-out plaster. Rinse the crack thoroughly and allow it to dry.

4. Brush the dried crack with the soft-tipped brush, then apply a bead of underwater sealer along its edges. Leave approximately 3/8 inch of space for the plaster fill.

5. Mix pool plaster per manufacturer's instructions to a thick, spreadable consistency.

6. Lightly moisten the crack perimeter with a damp grouting sponge. Apply plaster with the putty knife or trowel, pressing firmly into the crack and eliminating air bubbles. Smooth flush with the surrounding surface and match texture with the grouting sponge.

7. Refill the pool as soon as possible  plaster cures best underwater. If you have multiple cracks to patch, keep completed repairs covered with damp fabric to prevent premature drying and cracking.

Repair Method 3: Plaster Patching (Loose or Bubbling Plaster)

Best for: Areas where plaster is detaching, bubbling, or coming off in sections rather than a clean crack.

What you'll need:

• Safety goggles, ear protection, heavy-duty work gloves, sturdy footwear

• Hammer and masonry chisel

• Wooden pole (for tap-testing)

• Muriatic acid and soda ash

• Cement dye (to match existing plaster color)

• Pool plaster

• Pool trowel

• Grouting sponge

Steps:

1. Tap the pool floor and walls with the wooden pole. A hollow sound indicates loose plaster beneath the surface; chisel those areas off as well.

2. Use the hammer and chisel to remove all loose plaster. Clear away all debris.

3. Create shallow indents in the exposed surface with the chisel; this gives the new plaster something to grip.

4. Apply an acid wash: mix equal parts muriatic acid and water and apply carefully, then neutralize immediately with soda ash solution. This prepares the surface chemically for adhesion.

5. Add cement dye to the plaster mix if needed to match the existing pool color.

6. Dampen the prepared surface with a damp grouting sponge, then apply plaster with the pool trowel, pushing it into corners and indents. Feather edges into the surrounding surface. Eliminate all air bubbles.

7. Allow 15 minutes, then re-dampen and smooth again with the trowel. Cover with wet fabric until you refill the pool.

When You Should Call a Pool Repair Professional

DIY repair is appropriate for cosmetic surface cracks and isolated plaster issues. There are clear situations where professional assessment is the right call and attempting a DIY repair in these cases often costs more in the long run.

Call a professional when:

• The crack is wider than 1/4 inch, or you can see the shell material beneath the plaster

• The crack has offset edges (one side is higher or lower than the other) this indicates the structure has moved

• Multiple cracks are appearing in a short period

• The crack is growing or changing shape over weeks of observation

• The bucket test confirms active water loss that exceeds normal evaporation

• Dye testing shows water actively flowing through the crack

• You see soil settling, sinkholes, or moisture outside the pool near the crack

• The pool is more than 20 years old and has had multiple crack repairs

Per APSP/PHTA guidance: structural pool repairs that affect the shell or bond beam require a licensed pool contractor in most jurisdictions. Attempting to patch a structurally compromised area without addressing the underlying cause — soil movement, hydrostatic pressure, rebar corrosion, will result in the repair failing, often in less than one season.

A professional assessment typically includes leak detection, structural evaluation, and a recommendation for whether the crack is stable (can be patched and held) or progressive (requires structural intervention). That information is worth having before you invest time and money in a repair that may not hold.

How to Prevent Pool Cracks from Returning

Repairing a crack without addressing why it appeared is a temporary fix. Here's what actually prevents recurrence:

Maintain balanced water chemistry. This is the most overlooked cause of accelerated plaster deterioration. Water that is consistently low in pH or calcium hardness is corrosive, it leaches calcium from the plaster surface, causing pitting, roughness, and eventually cracking. Per PHTA standards, maintain pH at 7.4–7.6 and calcium hardness at 200–400 ppm. See our guide to what's the deal with pool chemical balance for the full picture.

Avoid abrupt water level changes. Rapidly draining and refilling a pool stresses the shell through expansion and contraction. If you need to drain for repairs or maintenance, do it slowly and avoid draining in freezing temperatures or immediately after heavy rain.

Manage groundwater and drainage. Poor drainage around the pool perimeter allows water to accumulate under and around the shell, increasing hydrostatic pressure that can crack the structure from the outside. Ensure your pool area has adequate slope and drainage away from the shell. For more on how poolside water management works, see our guide on how to troubleshoot your pool overflowing after rain.

Keep the pool full. An empty or partially drained pool in warm weather can allow the plaster to dry out, shrink, and crack. After repairs, refill as quickly as possible. A solar cover can reduce evaporation and maintain water level between refills, see how to use a solar pool cover for timing and coverage guidance.

Address tree roots proactively. Large trees near the pool can send roots under the shell over time, causing ground movement and cracking. If cracks keep appearing in the same area near a tree line, root intrusion is a possible cause worth investigating.

Maintain your equipment. A pump that's struggling or undersized for your pool creates pressure fluctuations that can, over time, stress plumbing and the areas where plumbing penetrates the shell. See our all pool pumps collection and our guide to common pool pump problems if equipment issues may be a contributing factor.

Frequently Asked Questions About Inground Pool Cracks

How do I know if my pool crack is serious?

A crack is serious if it's wider than 1/4 inch, has offset edges (one side higher than the other), is actively growing, is accompanied by water loss beyond normal evaporation, or appears alongside soil settling near the pool. Any of these signs warrants professional assessment before attempting repair.

Can I fix a pool crack without draining the pool?

Yes, for minor cosmetic hairline cracks, underwater epoxy putty or plaster formulated to cure underwater can fix the crack without draining. For longer, wider, or deeper cracks, draining provides a more thorough and lasting repair.

How do I know if my pool is leaking through a crack?

Perform the bucket test: place a bucket of pool water on a step, mark both water levels, and compare after 24 hours. If the pool drops more than the bucket, you have a leak. Dye testing near the crack can then confirm whether the crack is the leak source.

What is the best material for repairing pool cracks?

For minor cracks with a full pool: underwater epoxy putty or pool plaster formulated to cure underwater. For cosmetic cracks with a drained pool: pool plaster with an underwater sealer. For structural cracks: professional assessment first, the right repair material depends on the crack type and whether there's active movement.

How long does a pool crack repair last?

A properly executed cosmetic repair with the crack fully prepared, correct materials used, and the pool refilled promptly should last 5–10 years or longer. Repairs fail early when the crack wasn't fully exposed, the wrong material was used, the pool was left empty too long after repair, or the underlying cause (chemistry, drainage, tree roots) wasn't addressed.

Can I repair a cracked pool myself?

Yes, for cosmetic surface cracks. The full-pool underwater plaster method is a straightforward DIY repair. The drained-pool plaster repair is more involved but manageable with the right tools and preparation. Structural cracks those that penetrate the shell, show offset edges, or are accompanied by water loss should be professionally assessed before DIY repair is attempted.

When should I call a professional for a pool crack?

Call a professional when: the crack is wide or deep, the edges are offset, the crack is growing, you have confirmed water loss through the crack, multiple cracks are appearing, or the pool is structurally old with a history of repair. Per APSP/PHTA guidance, structural pool repairs require licensed contractor work in most areas.

This article was reviewed by a Certified Pool Technician (CPT). Structural crack assessment guidance references APSP/PHTA standards for pool safety and repair. Always consult a licensed pool contractor for cracks showing signs of structural movement, active leaking, or progressive growth before attempting DIY repairs.