Swimming Pool Plaster Problems: Typical Causes for Common Issues

Key reasons why interior finish can develop stains, etching, and other issues

Because it’s what you see every time you look at your swimming pool and because it acts as a protective layer between the pool water and the structural shell, your pool’s interior plaster finish is vital to both the beauty and integrity of your aquatic retreat.

Smooth plaster coating throughout the interior prevents water from leaking through into and potentially damaging the concrete (gunite/shotcrete) and other building materials that comprise the pool’s structural shell.

Along with its functional purpose, pool plaster serves an aesthetic one. Whether white, colored, or with quartz or pebbles blended into it, plaster makes the pool’s interior visually appealing. It’s among the most visible elements of your pool, and it can affect the appearance of the water color and how the water glistens in the sunlight.

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 issues with pool plaster and their typical causes

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.

So, what causes plaster damage like stains, streaks, erosion, etching (pitting), mottling (discoloration, and hairline cracks? One of several factors may be the culprit.

Out-of-balance pool water chemistry

One common cause of plaster deterioration is improper pool-water chemistry. In some cases, chemical balances may be off when a new pool is filled with water for the first time.

In others, chemistry is disrupted when a large amount of water gets added to an existing pool—usually to address loss due to evaporation.

Another reason chemistry can lose its balance is rain. When water from a big downpour lands in a pool, the levels of pH, free chlorine, and total alkalinity almost always takes a big hit. That creates an unfavorable environment for pool plaster that can lead to a host of problems if not corrected.

Organic matter that blows into the water and sinks to the pool bottom

Another external disruptor to pool chemistry is surrounding landscaping. Debris and other organic matter from trees, grass, leaves, plants, bark, and flower pollen can throw water balance out of whack.

Organic matter can also generate stains. Certain flowers, berries, and tree leaves that blow into the pool and sink to the bottom are frequently to blame for a variety of stains—some which form within a few hours.

Some foliage is particularly notorious for staining, like leaves with high tannin levels, such as some nut trees and oak trees. Acorns are another enemy to plaster that creates nasty stains.

Other foreign elements and objects that enter the pool

Among the most frequent perpetrator of plaster stains: fertilizer that blows into the pool. Many forms of this common household product contain iron, a mineral that can generate dime-size rusty brown spots along the interior.

Another source of unsightly rust stains: garden hoses left in the pool with the metal head touching the plaster, certain backyard children’s toys with metal parts that fall or get tossed into the pool and sink to the bottom. Other stray objects that fall into the pool, like garden tools, or may be at fault, as can objects that get left behind like coins or hairpins.

Note for older pools: A non-foreign object can be the villain. Rust stains sometimes develop from accessories that contain metal, such as handrails or ladders. Typically, staining is limited to the small area where the metal section touches the plaster.

Shifting ground beneath the pool

When it comes to hairline or eggshell cracks—thin lines primarily close to the plaster surface—the cause may be shifting soil.

Keep in mind, for the most part, these cracks are usually only a cosmetic problem, vs. a structural one. They do create another problem though; these tiny crevices can serve as an ideal home for algae to take hold. Once it settles in, algae can be difficult to remove using pool chemicals alone.

Take action when pool plaster develops blemishes and other irregularities

Don’t let problems fester. If they remain unchecked, the damage is often harder to tackle. Before attempting any repairs yourself, consult a professional pool company that specializes in pool remodeling.

You can take clear photos of the plaster problem and send them to the contractor. In some cases, an expert will be able to diagnose the problem from the photos and give you guidance by phone or email. In other cases, they will need to come out and assess the plaster’s condition.

Sometimes the solution is simple and affordable. Once an expert diagnoses the issue, they can provide treatment or other recommendations before any problems worsen.

Examples of quick fixes include balancing the water, brushing out stains, using a high dose of chemicals for a short time, or using a plaster patch kit. Topical stains respond particularly well to these quick fixes.

However, when an easy answer is not at hand, a pool expert will let you know that more complex steps are in order. Often the solution requires an acid wash and/or sanding. Depending on the location of the blemishes, both approaches involve partially or fully draining the pool.

Once drained, a powerful muriatic acid is applied to the interior finish. It strips away a thin layer of the plaster’s marcite material (marble dust) to remove surface stains and some textural abnormalities, such as calcium build up. Or, sanding may be used to buff out a stain or other blemishes, such as eggshell or hairline cracks.

Sanding and acid washing cannot resolve many issues, but not severe ones. For deep stains and extensive etching, as well as other kinds of serious deterioration, the big gun may be needed: a complete—and costly—replaster of your pool.

Prevent plaster problems in the first place

Your pool’s plaster is essential. So monitor any changes in the surface because doing so can prevent larger-scale problems down the road.

First and foremost, practice a consistent pool care routine. Above all, this means keeping the water properly balanced. Routinely test your water and adjust chemical levels as needed.

Check your pool regularly for any debris or objects in the water. Manual cleaning is a chore, so consider keeping your pool covered when not in use or use an automatic cleaner to help eliminate the majority of stain-causing materials.

For extensive plaster problems when a re-plaster of the entire interior is needed, consider this tip: Opt for a color quartz or pebble finish to reduce the odds of these problems occurring. These upgraded finishes provide a longer lifespan, and when problems do occur, they are typically less severe and less visible.