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How Is A Fiberglass Pool Made?

“Isn’t a fiberglass pool just a giant bathtub?”  We get this one a lot!  Although a fiberglass pool is a one-piece shell, I wish it was as simple as “it’s just a bathtub,” but it’s not…and we totally get it.  It’s just not something you see every day.  You may have seen a fiberglass pool shell along the side of the road to advertise a pool company, or maybe even on the back of a truck, and thought the same thing.  How a fiberglass pool is actually made is more complex than most think.  In short, to help you understand that a fiberglass pool isn’t just a bathtub 😊, here we will address exactly what a fiberglass pool is and the manufacturer’s steps to making the fiberglass pool shell.

What exactly IS a Fiberglass Pool?

A fiberglass pool is a one-piece pool manufactured in a quality control facility.  Initially the pool is created off a plug/pattern.  From the plug, it is transformed into a master mold.  From the mold, you get to make as many pools as you want or need.

Manufacturer’s Steps to Making the Fiberglass Shell

 Step 1:  Plug / Patternfiberglass_pattern_to_mold_to_ pool_shell

Build the plug, also known as the pattern. Think of the pattern as an exact true-life replica of a pool. The plug is made up of wood or steel, fiberglass, body filler, and primer.

Step 2:  Mold

Build the mold, also known as the shell.  From the plug, manufacturers create what is called a mold. The mold is then released from the plug.  This allows the mass production of one pool shape.  This mold does need to be cleaned.

Step 3: Gel Coat

Fiberglass pools are made inside out! The Gel Coat is actually the color selection that you chose for your pool.  The gel coat is made up of a colored resin that is applied to the mold through a spray gun.  This gel coat is applied in three separate layers in order to achieve a strong gel finish (up to 30 mil).  If this step is not applied properly, this could lead to the gel coat being too thin which could lead to blistering of your pool finish.  In comparison, if it ends up too thick, it could result in the first layer in your pool surface cracking.   Our fiberglass manufacturer uses polymerization to ensure durability (non-scientific definition: bonding two or more molecules together, using a cross-lynx process, to create strength and durability).  They also use infrared heaters to ensure the proper temperature (preferably around 77 degrees), as well as well as other devices to ensure proper moisture and air quality.

Step 4: Vinyl Ester Resin Barrier Coat

After the gelcoat has cured the Vinyl Ester Resin Barrier Coat (water barrier) gets sprayed next.  The gel coat is actually semi-permeable, this means that certain water molecules can pass through the outer layer of the gel coat.  If the layer underneath is polyester, a reaction could occur, causing blistering or corrosion.  This is why a vinyl ester layer is installed underneath the gel coat.   It is a good idea to make sure that your builder uses a manufacturer that installs this layer in their fiberglass.

Step 5:  Chopped Fiberglass (Coat #1)


Chopped fiberglass is material that is made up of three components that is applied simultaneously using a chop gun: polyester resin, chopped fiberglass roving, and catalyst.  This adds a layer of strength and durability.  Once the layer of chopped fiberglass is applied, it is then rolled using rollers to help prevent air bubbles.  This layer then needs to be cured.

Step 6: Chopped Fiberglass (Coat #2)

Apply a second layer of chopped fiberglass.  Once the first coat of chopped fiberglass is applied and cured, another coat is applied.  This adds an additional layer of strength and durability to the first layer.  After this second coat is applied, it is then rolled to help prevent air bubbles and then must be cured.

Step 7:  Hand Laid Woven Roving Fiberglass

Apply a layer woven roving fiberglass.  Some manufacturers substitute this step with an additional layer of chopped fiberglass.  It is crucial to make sure it is thick exactly where it needs to be thick (only in certain spots such as corners and where the pool wall meets the pool floor).  If the chopped fiberglass is too thin in certain areas, this will create “thin spots” which can lead to cracks in the gel coat.  If the chopped fiberglass is too thick in certain areas, this will create heavy spots which will force other areas to be considered “thin spots.”  That is why a layer of woven roving is placed during this step, leaving this layer even and free from “thick spots” or “thin spots.”

Step 8:  Chopped Fiberglass (Coat #3)

 Apply a third layer of chopped fiberglass.  After the third coat of chopped fiberglass is applied, it is then rolled to help prevent air bubbles, and then needs to be cured.  This adds yet another layer of strength and durability to the first and second layers.

Step 9: Honeycomb Core

Vertical strips of honeycomb core are inserted along the pool walls of the fiberglass.  In the industry, we refer to these as “ribs.”  These are installed to ensure structural integrity of fiberglass pool walls by adding strength to the fiberglass itself.  Without this step, the fiberglass is more flexible and susceptible to hydro static pressure.


Step 10:  Chopped Fiberglass (Coat #4)

 Apply a fourth layer of chopped fiberglass.  After the fourth coat of chopped fiberglass is applied, it is then rolled to help prevent air bubbles, and then needs to be cured.  This adds another layer of strength and durability to the first three layers.

Step 11:  Chopped Fiberglass (Coat #5)


 This is the final step in the process of making your fiberglass pool shell.  One last coat of chopped fiberglass is applied for a final layer of added strength and durability to all of the pool shell layers.  It is then rolled using rollers to help prevent air bubbles and then must be cured.

Once steps 1-11 are complete, your pool will make its way to the delivery truck and into your backyard where the shell will be dropped in the hole that was dug to spec for your pool, and the installation process will begin!!

Woah!  That’s a lot of steps!  Hopefully you are now able to see that this “isn’t just a bathtub.”  As stated above, this is a very complex process.  Generally, one pool per mold per day can be made.  When considering whether you should purchase a fiberglass pool, a vinyl liner pool, or a concrete pool, use these steps as a guide if you are considering pool strength and durability to make the decision that is right for you.  Now that you have an understanding for how a fiberglass pool shell is made, you can see just why a fiberglass pool is stronger per square inch. 

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