Fibreglass Pool Osmosis

Fibreglass Pool Osmosis - What Causes It? How Do I Fix It?

Fibreglass pools are a popular option among homeowners seeking pools with a smooth and long-lasting interior finish. Although fibreglass pools make a top choice due to their texture and clean appearance, this type of pool is prone to unique problems.

In this article, we will discuss what fibreglass pool osmosis is, what causes it, and whether or not it is something that you should be concerned about.

We also include some information about how you can stop osmosis from happening in your pool, as well as ways that you can fix the damage caused by this condition.

What Is Fibreglass Pool Osmosis?

Pool osmosis is a unique type of deterioration that affects fibreglass pools specifically. Some people in the pool industry refer to this decay as ‘the black plague’ because once it starts it spreads rapidly and can be very hard to treat.

In this process, water seeps through the gel coating of your fibreglass pool and gets in contact with the outermost fibreglass shell.

The water that enters these areas typically putrifies, and it may also absorb a trace amount of minerals from the fibreglass shell, creating a solution of oxidised metals.

What Causes Osmotic Blisters In A Fiberglass Pool?

The breakdown of the gel coating on fibreglass pools is what causes pool osmosis. As the gel coating degrades, small bubbles of air and water can pass through it and make contact with other layers of your pool’s lining.

When this happens, pockets of water can form in between these layers and accumulate debris, causing noticeable splotching on the gel coat of your pool.

Fibreglass pool osmosis is typically caused by poor construction. Sometimes, improper materials are used for this laminating layer, or it was simply installed by technicians that are lacking expertise.

In either case, the first sign of pool osmosis that you will notice is tiny bubbles on the inner surface of the pool. Eventually, these blisters will rupture and may release contaminants into the pool, such as algae, dirt, bacteria, and traces of metals.

Is Fibreglass Pool Osmosis Bad?

Fibreglass pool osmosis, although it can thoroughly impact your enjoyment of your pool, is typically only a cosmetic issue. This means that even if your pool osmosis is left untreated, it is not likely any severe damage will result from this condition.

Most often, pool osmosis bubbles that are left untreated will gradually spread to cover all surfaces of your pool until you have time or money to remedy this issue with your pool’s gel coating.

Fixing Pool Osmosis Yourself

Some advice that can be found online suggests that there are DIY approaches to solving pool osmosis blisters. This advice typically encourages pool owners to abrasively scrub the bubbles that appear on their pool’s surface until they break open before repatching these areas with epoxy. We strongly discourage this approach for a couple of reasons.

First, sanding the blisters down will further weaken the original gel coat layer. During this process, you are likely to diminish the structure of your pool even further, which will in turn allow even more water to penetrate the gel coating.

Even if you do sand these areas off effectively, there are not any epoxies available for domestic use that form a sufficient bond with the materials used in your pool’s gel coating. You may be able to achieve a temporary fix, but this extra layer you apply will only be a band-aid solution.

Once your DIY attempt at fixing this issue goes awry, you could have an even worse problem on your hands than when you started.

How To Fix Pool Osmosis The Right Way

The only way to truly fix pool osmosis or stop it from progressing in your pool is to have your fibreglass pool resurfaced.

Fibreglass pools should only be resurfaced by professionals with plenty of experience, and we recommend finding a service provider that provides a warranty on the work that they complete.

During the resurfacing process, your pool’s old gel coating is chipped away and removed using solvents until the outer fibreglass shell of your pool is exposed.

At this stage, any damage or debris left behind by past delamination will be resolved before a new layer of gel coat is carefully applied.

Louis from Pool Advisor


A chemical engineer by trade, Louis is committed to debunking myths in the pool industry by explaining the underlying chemistry and making it accessible to all.