Finding a crack in your swimming pool can be concerning, but not every crack indicates a serious structural problem. Concrete naturally expands, contracts, and experiences minor movement throughout its lifespan. In many cases, small cracks are simply part of the normal aging process.

However, some cracks may indicate a more significant issue, including alkali-silica reaction (ASR), soil movement, settlement, or structural stress.

The challenge is that many of these conditions look similar at first glance. Understanding the differences can help you determine when a crack is likely cosmetic and when it's worth having your pool evaluated by an experienced professional.

If you're unfamiliar with ASR, start with our guide explaining what alkali-silica reaction is and how it affects concrete swimming pools before diagnosing specific crack patterns.

The Short Answer

Most swimming pool cracks are not caused by alkali-silica reaction.

Hairline shrinkage cracks, minor settlement, and seasonal soil movement are much more common in residential concrete pools.

ASR generally develops slowly over many years and typically produces a distinctive combination of progressive cracking, internal expansion, and other visible symptoms rather than a single isolated crack.

Because multiple conditions can produce similar damage, a visual inspection alone is rarely enough to confirm ASR.

Common Reasons Concrete Pools Crack

Concrete is an extremely durable building material, but it is not completely crack-proof.

Some amount of movement is expected throughout the life of any concrete structure.

Common causes of swimming pool cracks include:

• Normal concrete shrinkage
• Soil movement
• Foundation settlement
• Structural loading
• Temperature changes
• Groundwater pressure
• Construction defects
• Alkali-silica reaction (ASR)

Each produces different crack patterns and progresses differently over time.

Comparing the Most Common Types of Pool Cracks

Cause	Appearance	Typical Severity	Does It Usually Get Worse?
Plastic shrinkage	Fine surface cracks shortly after placement	Low	Usually no
Drying shrinkage	Thin hairline cracks	Low	Usually stabilizes
Settlement	Larger directional crack	Moderate	Sometimes
Expansive soils	Wider structural movement	Moderate to High	Can worsen seasonally
Structural stress	Longer continuous cracks	Moderate to High	Depends on cause
Alkali-Silica Reaction (ASR)	Map cracking with expansion	Moderate to High	Yes, often progresses over time

While this comparison is helpful, the surrounding symptoms often provide the biggest clues.

What Does Alkali-Silica Reaction Look Like?

Unlike many other forms of cracking, ASR usually affects larger sections of concrete rather than creating one clean crack.

Common indicators include:

Map Cracking

One of the hallmark signs of ASR is a network of interconnected cracks that resembles a road map or spider web.

Instead of a single straight crack, numerous smaller cracks branch in different directions across the concrete surface.

White or Clear Gel Deposits

ASR creates an expansive gel inside the concrete.

As internal pressure builds, this gel may migrate toward the surface through existing cracks where it sometimes appears as a translucent, amber-colored, or white substance.

Although not every ASR-affected pool displays visible gel, its presence is considered one of the stronger indicators.

Progressive Expansion

Because ASR causes internal expansion, cracks often continue developing over several years instead of remaining unchanged.

Tile lines, coping, and adjoining concrete may also begin showing subtle movement as pressure increases within the pool shell.

What Does Settlement Cracking Look Like?

Settlement occurs when soil beneath or around the pool shifts after construction.

This movement creates stress within the concrete shell.

Settlement cracks often have different characteristics than ASR.

They are more likely to:

• Form one primary crack instead of many interconnected cracks
• Follow a fairly straight or diagonal path
• Occur where soil movement is greatest
• Stabilize after the ground finishes settling

Pools built on expansive clay soils may continue experiencing seasonal movement as moisture levels change throughout the year.

Can Expansive Clay Soils Be Mistaken for ASR?

Yes.

This is especially true in areas of Central Texas where expansive clay soils are common.

Clay soils naturally swell when wet and shrink during dry conditions.

That constant movement can place stress on the pool shell, sometimes producing structural cracks that resemble other forms of concrete deterioration.

Unlike ASR, however, expansive soils do not create chemical reactions inside the concrete.

Instead, they place external pressure on the structure.

An experienced engineer or swimming pool contractor can often distinguish between soil movement and ASR by evaluating the crack patterns, surrounding conditions, and overall structural behavior.

Hairline Cracks Are Usually Not ASR

One of the biggest misconceptions among homeowners is that every hairline crack indicates structural failure.

In reality, many hairline cracks develop during normal concrete curing.

These cracks are often:

• Extremely narrow
• Short in length
• Stable over time
• Purely cosmetic

If a hairline crack remains unchanged for years and shows no signs of movement or leaking, it is much less likely to indicate alkali-silica reaction.

When Cracks May Indicate a More Serious Problem

Although many cracks are harmless, certain warning signs deserve professional evaluation.

You should consider having your pool inspected if you notice:

• Cracks spreading across larger portions of the shell
• Map-like cracking patterns
• White gel deposits near cracks
• New leaks developing without obvious plumbing issues
• Coping or tile beginning to shift
• Concrete that appears to be bulging or expanding
• Cracks that noticeably increase in width over time

These symptoms do not automatically confirm ASR, but they suggest additional investigation may be appropriate.

How Professionals Diagnose ASR

Diagnosing alkali-silica reaction involves much more than looking at surface cracks.

Engineers may evaluate:

• Crack patterns
• Construction history
• Concrete age
• Moisture exposure
• Aggregate sources
• Petrographic analysis
• Laboratory testing
• Expansion measurements

Because several structural issues can produce similar symptoms, proper diagnosis is essential before beginning repairs.

Can a Pool Have More Than One Problem?

Absolutely.

Some pools experience multiple conditions simultaneously.

For example, a pool may develop minor shrinkage cracks during curing while also experiencing seasonal soil movement years later.

In rare situations, ASR may occur alongside foundation movement or groundwater-related issues.

This is another reason why accurate diagnosis is important before deciding on a repair strategy.

Should You Worry About Every Crack?

Fortunately, no.

Concrete is naturally prone to developing small cracks over time.

Most residential pools continue providing decades of reliable service despite minor cosmetic cracking.

The primary concern is whether cracks remain stable or continue progressing.

Pools showing significant structural movement, expanding crack networks, or recurring leaks deserve a professional evaluation to identify the underlying cause.

How Quality Construction Reduces Crack-Related Problems

No builder can promise that concrete will never crack.

However, experienced swimming pool contractors greatly reduce the likelihood of significant structural issues through proper engineering and construction practices.

That includes:

• Engineered pool designs
• Proper reinforcement placement
• High-quality shotcrete or gunite application
• Optimized concrete mix designs
• Tested aggregate sources
• Proper curing procedures
• Attention to local soil conditions
• Effective drainage planning

These practices help produce stronger, more durable pool shells capable of performing for decades.

Frequently Asked Questions

Can you identify ASR just by looking at a crack?

No. While certain crack patterns are more commonly associated with ASR, confirming the diagnosis typically requires additional evaluation and, in some cases, laboratory testing.

Do all pool cracks leak?

No. Many cosmetic cracks never penetrate completely through the pool shell and therefore do not leak.

Can settlement cracks stop moving?

Yes. Once the surrounding soil stabilizes, many settlement cracks remain unchanged for years.

Does ASR always cause map cracking?

Map cracking is one of the most common symptoms of ASR, but not every affected structure displays identical crack patterns.

Is a straight crack usually ASR?

Not usually. Straight or diagonal cracks are more commonly associated with settlement, structural loading, or soil movement than alkali-silica reaction.

When should I have my pool inspected?

If you notice expanding cracks, recurring leaks, shifting coping, widespread map cracking, or other signs of structural movement, it's a good idea to schedule a professional inspection to determine the underlying cause.