Is Fiberglass Waterproof?

Is Fiberglass Waterproof?

If you have your own boat, then you will know that it is very important for all components of your boat to be waterproof. For obvious reasons, your boat is going to get wet when it is out on the water.

So, if you want to keep your boat protected, it is important that waterproof materials are used to construct it. This not only goes for the original construction, but for any modifications, you make too! 

If you are doing any work on your boat, or modifying any of the components, you might find yourself contemplating using fiberglass. Fiberglass is really easy to work with, and perfect for lots of different jobs. But is fiberglass waterproof?

And is it suitable for use on a boat? In this guide, we’re answering both of these questions as we take a look at whether, or not, this material is waterproof. So, if you want to find out more, keep on reading! 

What Is Fiberglass?

First things first, let’s take a look at exactly what fiberglass is. Fiberglass is a commonly used type of fiber-reinforced plastic.

As the name suggests, the plastic used in fiberglass is reinforced through the use of glass fibers. It is generally a very strong material and is used for lots of different tasks. 

To create fiberglass, the fibers are generally arranged in a very random fashion.

However, in the creation of some types of fiberglass, the fibers may be flattened out into a sheet called a chopped strand mat, or woven into glass cloth. So, as you can see, there are lots of different styles of fiberglass out there. 

Fiberglass is generally used in projects because it is a strong material that is easy to work with.

Fiberglass can be molded into various complex shapes, which is why you will find many different things made out of fiberglass – including bathtubs, roofing, boats, and lots more. 

So, if you are considering using fiberglass on your boat, you might have a number of different ways in which you want to use it.

You may want to use fiberglass to create something to keep on your boat, or you may want to use it in the construction of your boat itself. However, in order to do this, you will need to know if it is waterproof, or not. So, let’s take a look.

Is Fiberglass Waterproof Or Not?

If you want to use fiberglass in the construction of your boat, then you will need this material to be waterproof. It is impossible to avoid your boat getting wet if you plan on using it as a boat is supposed to be used. So, is fiberglass waterproof?

While fiberglass is mostly water-resistant, it isn’t actually waterproof. So, this material on its own will not be suitable for constructing a boat.

However, that doesn’t mean that you cannot use fiberglass to make your boat. This material is perfectly okay to use, as long as you combine it with other materials. 

In order to make your fiberglass boat waterproof, you will need to cover the construction in resin. One of the best types of resin to use alongside fiberglass is a vinyl ester.

Vinyl ester is a strong resin that combines incredibly well with fiberglass. These two materials connect together very well and form a strong coat on the fiberglass, ensuring that water will not penetrate the resin and damage the fiberglass. 

So, no, fiberglass isn’t waterproof on its own. However, it can easily be made waterproof by using it with resin. So, if you need to make your fiberglass waterproof, simply use resin and your fiberglass will be protected. 

What Happens To Fiberglass In Water?

Is Fiberglass Waterproof?

While fiberglass isn’t waterproof, that doesn’t mean that it is completely ruined when it comes into contact with water. A small amount of water won’t damage the fiberglass. But continued exposure to water, like when you are in a boat, will.

When fiberglass comes into contact with water, the glass fibers that are used to reinforce the plastic will react with the water. This can cause the sizing of the reinforcement to become damaged, and this can make the fiberglass weaker.

This will only occur if the fiberglass is continually exposed to the water. So, if your fiberglass simply comes into contact with a small amount of water it won’t be an issue. 

However, to keep the fiberglass used in the construction of your boat protected, you should always cover it with resin. This will protect the fibers and ensure that the fiberglass remains as strong as it was on the day you started using it. 

Does Fiberglass Need To Be Sealed?

In some cases, fiberglass will not need to be sealed when it is used to construct things. However, if you are using fiberglass around water, then it will need to be sealed. 

As we have just established, water can penetrate the sheeting that is used to gather the fibers used to reinforce fiberglass. This water can impact the sizing of the sheeting, and this essentially means that it will weaken the reinforcement.

So, prolonged exposure to water can cause the fiberglass to warp and become damaged. This will prevent it from doing its job properly. 

So, if you are using fiberglass in any projects where the fiberglass will be exposed to water, you absolutely should seal the fiberglass.

The best sealant to use for the job is a resin as this will protect the fiberglass and prevent the water from penetrating the sheeting! 


In short, on their own fiberglass reinforcements aren’t totally waterproof. That being said, they easily can be made waterproof through the use of resin.

When fiberglass and resin are combined, they create a totally waterproof material that will be waterproof. 

So, fiberglass alone isn’t waterproof. This material can easily be made waterproof. So, if you need to use it for any tasks on your boat, then you can easily do this – as long as you combine the fiberglass with resin. 

We hope this information has been helpful – thank you for reading! 

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