Do Plaster Cracks Mean Your Concrete Pool is Leaking?

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Do Plaster Cracks Mean Your Concrete Pool is Leaking?

If you’re a conscientious pool owner, you pay attention to the condition of your swimming pool on an ongoing basis. As we always emphasize here at Certified Leak Detection, changes in the appearance, water level or mechanical performance of your pool could be a sign of a leak – and therefore requires immediate attention before the issue becomes more extensive and expensive to repair.

Owners of concrete pools have a bit more of a challenge, as not all cracks that occur in the plaster finish indicate a leak. Our blog post – “How Can I Tell If My Concrete Pool Has a Leak?” – covers this topic in greater detail. So while it seems we answered our own question very early, such cracks can be evidence of other problems that need to be addressed.

As the good people at Blue Haven Pools & Spas note, even when a high-quality plaster finish is properly applied to a pool, complications can arise. Blemishes sometimes appear as soon as a few months after your pool is built, or they can show up several years later.

“Plaster in good condition is essential for your pool’s overall longevity and durability. However, even in a well-maintained pool, eventually plaster will age and show signs of degradation. That’s perfectly normal. Depending on a variety of local factors and your individual pool-water treatment routine, the typical lifespan of traditional marcite plaster is 7 to 10 years. If the finish includes a quartz aggregate blend, the time table should extend another five years.”

Common Causes of Pool Plaster Cracks

Cracks can develop for a wide variety of reasons. The most common include the following:

Imbalanced water chemistry – According to Blue Haven Pools & Spas, water chemistry can become disrupted because of a large amount of water being added to the pool due to evaporation. Rain – to which Central Florida is no stranger during the summer – is also a cause. When water from afternoon thunderstorms or (fingers crossed they miss us) hurricanes dumps into a pool, the levels of pH, free chlorine and total alkalinity take a big hit. This creates an unfavorable environment for pool plaster that can lead to numerous problems if not corrected.

Shocking your pool after heavy rains is recommended. As our blog post – “The Shocking Truth About Shocking Your Pool” – points out, rain water can bring with it dust, air pollutants, algae spores and pollen that can disturb your pool water chemistry, consume your chlorine and discolor your water. Also, heavy storms bring with them parts of overhanging trees and overflowing planters – as well as soil from the adjoining lawn laden with bacteria, phosphates and other debris.

Shrinking pool plaster – Craze cracks are small clustered cracks that occur when the pool plaster shrinks. As Marcus Sheridan – owner of River Pools – says, “Plaster tends to shrink as water in the plaster mix gets absorbed during the curing process, but if there is too much shrinking, craze cracks can appear. Pool plaster crazing is a pretty common problem, and the consequences are usually minor. When the crazing is too bad, however, it can cause staining, algae issues, and calcium nodules. A bad case of crazing will require you to replaster your swimming pool.”

Shrinking concrete – According to BuyersAsk, it’s very common for concrete to experience shrinkage cracks when it is first placed. “Excessive temperatures, improper curing, wind or excess water in the concrete mix can also contribute to shrinkage cracking. These types of cracks are generally small, shallow, in random locations and do not result in leaking.”

Shifting soil beneath the pool – Thin hairline or eggshell cracks close to the plaster surface may be caused by shifting ground. Although such cracks are usually only cosmetic versus structural, they’re a concern, as they can serve as harbors for algae to take hold. Once established in this way, algae can be hard to remove using pool chemicals alone. In addition, too much ground movement under and around the swimming pool may eventually cause structural cracks.

Surface Cracks Versus Structural Cracks – How to Tell the Difference

Plaster cracks such as those described above occur at the surface of the finish and rarely progress into the concrete shell. Although shallow, surface cracks do need to be repaired to maintain the integrity of the pool finish and prevent algae from gaining a foothold.

If a crack is structural, there is a good chance that the pool is leaking or will eventually leak. These cracks occur in the shell of the pool and may appear in various locations as vertical or horizontal cracks on the sides or bottom of the pool. The majority of structural cracks running through the concrete (gunite or shotcrete) will also be mirrored through the plaster coating or the tile area over the bond beam. Cracks in a pool that’s significantly out of level are an indication of a serious problem.

The Main Causes of Structural Pool Cracks

Structural leaks typically occur when there is a crack in the pool’s shell. Jason Hughes of River Pools cites the following causes:

  • Poor construction or engineering
  • Ground movement
  • Pressure from groundwater
  • Settling due to shifting soil

Cracks from construction or engineering issues fall into three main categories:

Bond beam cracking

This type is one of the most common cracks that develop horizontally at the bond beam or waterline tile area. It is an area where the tile circles the pool at the waterline level. A pool with a concrete walk or deck area must have an expansion joint between the concrete deck and pool. But if there is no expansion joint or no place for movement, a crack can occur. A concrete deck can expand due to soil movement or wide variation in temperature, causing expansion and contraction, resulting in cracks. 

Besides noticing the cracks, missing/cracked tile and cracked, loose, or damaged coping are other signs that indicate this problem.

Rebound cracking

Rebound refers to the material that bounces or flies off the rebar and existing concrete. Rebound material is weaker than the original material because it has a higher concentration of sand and less cement. Contractors reuse it on the bottom of the pool, the seating benches in the pool below the pool, or in the step entry areas to save labor and material. Using rebound material for construction is poor workmanship and can result in weakened areas or cracks. They often occur at the entry step area. Typically, they don’t go deep into the shell, and may not cause a leak.

Mirrored or reflective cracking

BuyersAsk provides the following explanation for this type of cracking:

“Tile and plaster often mirrors a crack that is behind them i.e. if there is a crack in the bond beam, the tile may crack in the same area that the bond beam is cracked. The same is true with cracks in the plaster.

“Cracks may also appear in areas where the concrete covering the rebar or piping is insufficient. When the rebar has insufficient cover, then there may be a pattern of cracks that reflects the rebar pattern. Over time rust may come out of these cracks and that can be a significant concern, as the rebar rust expands in volume up to four times its diameter. This expansion creates tremendous pressure on the concrete, causing spalling, cracks and damage.”

The Take-Home Message

Being proactive in keeping your concrete pool in good repair can go a long way in preventing leaks. Our blog post – “Concrete Pool Maintenance – What You Need to Know” – provides valuable information and advice. However, calling our experienced team at Certified Leak Detection if you suspect a leak will help keep a bad situation from becoming much worse.

We use technology and techniques we have developed over 20 years in business. In addition to quick detection of pool leaks, we provide industry-leading leak detection for spas and hot tubs, as well as slabs and foundations. Serving areas throughout Central Florida – including Orlando, Longwood, Lake Mary, Sanford, Kissimmee, Clermont and Winter Springs – our team is ready to answer your call. Contact us for quick, reliable service!

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