Fiberglass Swimming Pool Blisters

Blisters are a Serious Risk To The Survival Of Your Swimming Pool & Spa

In my many posts, and on all our websites, we specifically mention to never empty a fiberglass pool without professional help. By professional help, I mean a pool service company experienced in the care of fiberglass pools. Unfortunately, most pool service pro's lack any understanding of fiberglass and fiberglass concrete (hybrid) swimming pools. So be sure to ask questions about experience.

Sanded fiberglass pool wall with numerous blisters

All fiberglass swimming pools will develop blisters after 15 to 20 years. Blisters begin small and grow over time and, if not treated properly, will eventually eat a hole through the multiple layers of fiberglass and resin.

The photo above shows what will happen after 30 or more years. Notice the one blister that has gone through all 3 layers of fiberglass and resin, all because the pool wasn't properly cared for after the initial 20 years.

What Causes Blistering?

The finish coating on fiberglass is always some form of gel coat. For surfaces constantly submurged in chemically treated water, the finish coat must bee swimming pool gel coat. Unlike other types of gel coat, i.e. marine, automobile, food service, etc. swimming pool gel coat is heavier, and is a full 1/16" thick..

The advantage of swimming pool gel coat, as opposed to epoxy or pool paint, is it's non-porous quality. Because it's non-porous, it doesn't stain at the water line, algae cannot cling, and the pool water is 8 to 10% warmer. Less than half the chemicals are needed as compared to any other swimming pool. At least for the first 15 to 20 years, excluding only San Juan Pools which last 25 to 30 years before blisters appear.

The blisters begin as the gel coat gradually becomes porous allowing the chemically treated water to ooze through the gel coat and attack the fiberglass beneath. The blisters form because the water is unable to get through the fiberglass, but the pressure is sufficient to push the now porous gel coat into the pool forming a small blister.

Over time the blisters grow, as the gel coat becomes more porous, and some blisters eventually split open exposing the fiberglass beneath. But more important than the size of the blisters is the damage to the fiberglass. Given enough time, the water inside the blister eats through the layers of fiberglass and, eventually, causes a major leak. See the above photo.

Learn How to Rid Your Pool of Blisters for the Next 20 Years