Repair Services
Fiberglass Pool Blister Repair Done Right
Blisters and bubbles in your pool's surface mean water has gotten behind the gel coat, and it's not leaving on its own. We open every blister, dry the laminate, rebuild the damaged layers, and recoat with factory-grade marine gel coat that keeps water where it belongs.
Fiberglass pool blister repair has exactly one correct method: open the blisters, dry out the laminate underneath, rebuild the damaged fiberglass, and seal the pool with new marine-grade gel coat. Sanding blisters flat or coating over them fails, because the water that caused them is still trapped inside the shell, and it will push new blisters through any surface you put on top.
What Causes Blisters in a Fiberglass Pool?
Pool blisters are osmotic blisters, and the mechanism is worth understanding because it explains why quick fixes never work.
Gel coat looks waterproof, but at the molecular level it's semi-permeable, water molecules can slowly migrate through it, especially where the coat is thin, aged, or porous. Once water reaches the laminate behind the gel coat, it finds water-soluble compounds left over from manufacturing: uncured resin components, binder chemicals, tiny voids in the layup. Water dissolves them into a concentrated fluid.
That's where osmosis kicks in. Nature wants to dilute that concentrated pocket, so more water gets pulled through the gel coat toward it, one-way traffic. Pressure builds inside the pocket until it physically lifts the gel coat off the laminate. That dome you can feel underfoot is pressurized fluid, and if you pierce a fresh one, it often weeps an acidic, vinegar-smelling liquid. That smell is the fingerprint of osmotic blistering.
Boat owners have battled the same disease for decades under the name "boat pox." Your pool shell is built like a hull, so it fails like one. The difference: your pool sits in treated water year-round, with no dry season in a boatyard.
Blisters show up most often in pools where the original gel coat was applied thin or with a lower-grade resin, more on that below. For the homeowner's field guide to spotting them early, see our symptom guide to fiberglass pool blisters.
Why Blisters Spread, and Why Waiting Costs You
A blister is not a stable condition. It's a process that's still running.
Every blister is a spot where the gel coat has already delaminated from the shell. The trapped fluid keeps drawing in more water, so blisters grow. The stretched, lifted gel coat around each dome cracks and admits water faster. And the laminate under a long-standing blister stays saturated, which weakens the resin, wicks moisture along the glass fibers, and seeds the next generation of blisters nearby.
That's why a pool with "a few bubbles" one spring can have dozens two seasons later. The progression usually runs:
- Stage 1: A handful of small, isolated domes, often on the floor or steps, sometimes only visible when the light rakes across the surface.
- Stage 2: Blisters multiply and cluster. Some pop and leave craters with exposed, discolored laminate.
- Stage 3: Broad areas of gel coat delaminate. The surface feels hollow when tapped, and the laminate itself is water-saturated and softening.
Repair cost climbs with each stage, a Stage 1 pool needs targeted repairs and a recoat, while a Stage 3 pool needs extensive laminate rebuilding. Catching it early is the cheapest decision you'll make as a fiberglass pool owner. Our repair cost guide shows how the typical ranges shift as damage spreads.
Blisters are a progressive condition, not a cosmetic one. Open, dry, rebuild, recoat, in that order, with no shortcuts on the drying. Any repair that leaves moisture in the laminate is a scheduled failure.
How We Repair Fiberglass Pool Blisters: Open, Dry, Rebuild, Recoat
Blister repair is step three of our 5-step treatment plan, after safe draining and a full shell inspection. Here's what actually happens to your pool:
Open every blister
Each blister is ground open and back to solid material, dome, crater rim, and any delaminated gel coat around it. We also sound the surrounding surface for hollow spots, because for every blister you can see there are usually a few you can't. Opening them releases the trapped fluid and exposes the true extent of the damage.
Dry the laminate
This is the step that separates a cure from a relapse. The exposed laminate must dry thoroughly before anything goes back on it, because resin will not bond reliably to wet glass, and sealed-in moisture simply restarts the osmosis clock. We wash the opened areas to remove the dissolved contaminants, then let the laminate dry down before rebuilding. Patience here is non-negotiable.
Rebuild the damaged layers
Craters and ground-out areas are rebuilt with new resin and fiberglass, restoring the laminate to full thickness, then faired flush with the surrounding surface. Where blistering was widespread, we rebuild across the whole affected zone rather than dot-patching, a patchwork of fifty little repairs is weaker and uglier than one properly rebuilt surface.
Recoat with marine gel coat
Finally we spray the pool with factory-grade marine gel coat, the same high-quality, water-resistant material used on new pool shells and boat hulls. Applied at proper thickness in multiple passes, it chemically bonds to the prepared shell and re-establishes the moisture barrier the original surface lost. Because blisters signal that the original gel coat is permeable, we recoat the full pool interior, not just the repair spots. That's a complete gel coat resurfacing, and it's why our blister repairs don't come back.
Prevention: Why Gel Coat Quality Decides Whether Blisters Return
Here's the honest truth about blisters: they're usually a materials problem before they're a maintenance problem. Two pools in the same backyard water can age completely differently depending on what their surfaces are made of.
A quality marine gel coat, applied at proper thickness, is a highly water-resistant barrier, it's engineered to live submerged for decades on boat hulls. A thin coat, a bargain resin, or a rushed application leaves a porous surface that water migrates through years sooner. And epoxy pool paint is worse still: it sits on top of the surface rather than bonding into it, so water gets behind it easily and it bubbles and peels within a few seasons. If a contractor's answer to your blisters is paint, you're talking to the wrong contractor, see gel coat vs. epoxy pool paint for the full comparison.
Water chemistry plays a supporting role. Aggressive, low-pH water attacks gel coat and accelerates permeability, so keeping your water balanced buys your surface years. But no amount of perfect chemistry will save a surface that was thin or porous from day one.
Our prevention prescription is simple: restore the pool once with factory-grade material, applied the way the factory applied it, and maintain balanced water afterward. That's a 15-25 year surface, backed by a written warranty on every job.
Think Your Pool Has Blisters? Diagnosis Is Free
Snap a few photos, wide shots of the pool plus close-ups of the bumps or craters, and send them through our Free Pool Checkup. A fiberglass specialist (not a salesperson) will review them and call you within one business day with a diagnosis, a treatment plan, and an honest estimate. If it's not blistering, we'll tell you that too.
Send photos and a fiberglass specialist calls you with a diagnosis and a real number.
- Free photo-based estimates
- Factory-grade gel coat, never paint
- Written warranty on every job
Straight Answers
Fiberglass pool blister repair FAQs
What causes blisters in a fiberglass pool?
Osmosis. Water slowly migrates through the gel coat, dissolves compounds in the laminate behind it, and osmotic pressure pulls in more water until the fluid pocket lifts the gel coat into a dome. Thin or low-grade gel coat makes it happen sooner.
Can I just pop or sand down the blisters?
No, that treats the bump, not the disease. The laminate behind the blister is wet and contaminated, and any coating applied over it will blister again. A lasting repair opens the blister, dries and rebuilds the laminate, then recoats.
Will pool blisters go away on their own?
Never. Osmotic blisters only grow, multiply, and eventually delaminate whole sections of gel coat. The earlier they're repaired, the smaller and cheaper the job.
Do you have to resurface the whole pool to fix blisters?
Usually, yes, and it's in your interest. Blisters prove the original gel coat is permeable, so spot-patching leaves the rest of the surface on the same failure clock. Rebuilding the damaged areas and recoating the entire interior with marine gel coat cures the pool once instead of chasing blisters forever.
How long does fiberglass pool blister repair last?
Repaired and recoated with quality marine gel coat at proper thickness, expect a 15-25 year surface with balanced water chemistry, the same lifespan as a new factory shell. We back it with a written warranty.
Ready for your pool's prescription?
Send photos of your pool and a fiberglass specialist, not a salesperson, will call you within one business day with a diagnosis and a real number.
