Learning how to repair fibreglass pool surfaces might seem like a job for a high-priced professional, but you can actually handle most minor repairs yourself if you've got a free weekend and some basic tools. Fibreglass is incredibly durable, but it isn't invincible; over time, the sun, chemicals, and ground movement can cause those annoying spider cracks or small chips in the gelcoat. If you've noticed a few blemishes or a small leak, don't panic—fixing it is more about patience and preparation than having a degree in engineering.
Figuring out what you're dealing with
Before you go out and buy a bunch of resin, you need to take a good look at the damage. Not all cracks are created equal. Most of the time, what you're seeing are spider cracks. These are tiny, hairline fractures that usually only affect the gelcoat—the outer colored layer of the pool. They look ugly, but they aren't usually a sign that your pool is about to fall apart.
On the other hand, if you see a crack that's wide enough to stick a fingernail into, or if the pool wall feels "squishy" or bulged, you might have a structural issue. If the shell itself is cracked, water could be leaking out and washing away the dirt behind the pool, which is a much bigger headache. For the sake of this article, we're focusing on how to repair fibreglass pool issues that are cosmetic or minor enough for a DIY fix.
Getting your gear ready
You can't just slap some duct tape on a pool crack and call it a day. To do this right, you'll need a specific set of supplies. Most hardware or marine supply stores sell fibreglass repair kits, which are a lifesaver because they usually come with the resin and hardener you need.
Here's a quick list of what you should have on hand: * A variable-speed orbital sander (or some serious elbow grease and sandpaper) * Fibreglass resin and a catalyst (hardener) * Glass foam or matting (if the hole is deep) * Gelcoat that matches your pool's color * Acetone for cleaning * Safety gear like gloves, goggles, and a respirator mask (the fumes are no joke) * Putty knives and some mixing buckets
Step 1: Prep the area like a pro
The secret to a repair that actually lasts is all in the prep work. If you try to apply resin to a dirty, wet, or smooth surface, it's going to peel off within a month. First, you need to drain the pool water until it's about six inches below the repair site. Give it plenty of time to dry out completely.
Once it's dry, grab your sander. You want to sand the area around the crack to remove any loose gelcoat. A pro tip here is to "V-out" the crack. This means using a small grinding tool or heavy-grit sandpaper to turn that thin crack into a V-shaped groove. This gives the new material more surface area to bond to. It feels wrong to make a crack wider, but trust me, it's the only way to make the repair permanent.
Step 2: Cleaning and degreasing
After sanding, the area will be covered in fine white dust. Wipe it down thoroughly with a damp cloth, and then follow up with acetone. The acetone is crucial because it strips away any oils or leftover chemicals that would prevent the resin from sticking. Be careful not to use too much, though, as it can soften the surrounding gelcoat if you let it puddle. Once it evaporates, you're ready for the sticky part.
Step 3: Applying the resin and filler
Now it's time to mix your resin. Follow the instructions on your kit exactly—if you add too much hardener, the resin will get hot and brittle; too little, and it'll stay tacky forever.
If you're dealing with a deep chip or a structural crack, you'll want to layer in some fibreglass matting. Cut the matting to the shape of the hole, soak it in the mixed resin, and press it into the "V" you ground out earlier. Use a putty knife to smooth it out and pop any air bubbles. If it's just a surface scratch, you can use a fibreglass filler (which is basically resin mixed with a thickening agent) to fill the gap.
Let it cure. This is the part where most people get impatient. Depending on the temperature and humidity, this could take a few hours or a full day. It needs to be rock hard before you even think about the next step.
Step 4: Sanding it flat
Once the resin has cured, it probably looks like a bit of a mess. That's fine. Take your orbital sander and start with a medium-grit sandpaper (around 80 or 100 grit) to level out the hump of resin. Once it's level with the rest of the pool wall, switch to a finer grit (220, then 400) to get it smooth.
You're looking for a finish that feels seamless to the touch. If you run your hand over it with your eyes closed, you shouldn't be able to tell where the repair starts and the original pool ends.
Step 5: The gelcoat finish
This is the hardest part of learning how to repair fibreglass pool shells: the color match. Fibreglass pools fade over time due to UV exposure, so even if you buy the "original" color from the manufacturer, it might look brighter than the rest of your pool.
Apply the gelcoat over the sanded resin using a brush or a spray gun if you're feeling fancy. You'll want to apply it slightly thicker than the surrounding area because you're going to sand it again. Once the gelcoat is dry—and again, give it plenty of time—hit it with some very fine wet-sandpaper (1000 to 2000 grit). This will bring back that factory shine.
Step 6: Buffing and polishing
To really make the repair disappear, grab some rubbing compound and a high-speed polisher. Buff the area until the dullness from the sandpaper turns into a glossy finish. If you've done it right, you'll have a hard time finding where the crack even was.
Finally, give the whole area a good rinse to get rid of any polishing compound before you start refilling the pool. When you refill, do it slowly to make sure the pressure doesn't cause any immediate issues, though if the resin cured properly, it should be stronger than the original shell.
Why things sometimes go wrong
If you find that your repair pops out after a few weeks, it's usually because of one of three things. Either the area wasn't dry enough, the "V" groove wasn't deep enough, or the chemical mix was off. Fibreglass is finicky about moisture; even a little bit of dew can ruin a bond.
Another common issue is "osmotic blistering." If you see little bubbles appearing under the gelcoat, that's usually water that has gotten behind the finish. Repairing those is the same process, but you have to make sure you've popped and dried every single one, or they'll just keep coming back like a game of Whac-A-Mole.
Keeping your pool in good shape
Now that you know how to repair fibreglass pool cracks, you probably don't want to do it again anytime soon. The best way to prevent future damage is to keep your water chemistry in check. High chlorine levels or wild pH swings can make the gelcoat brittle over time.
Also, watch out for the "ring around the tub." Oils and minerals can build up at the waterline and eventually eat away at the finish. A quick wipe-down once a week with a pool-safe cleaner can save you a lot of sanding and resin-mixing in the long run.
Taking care of a fibreglass pool isn't a massive chore, but staying on top of the small stuff makes a huge difference. If you see a tiny crack, fix it now. It's a lot easier to spend an hour on a small chip today than it is to spend a whole weekend fixing a spider web of cracks next summer. Just take your time, follow the steps, and don't be afraid to get your hands a little dirty.