How to Fix a Hairline Crack in a Fiberglass Tub?

Have you ever come across a situation when you saw cracks in your fiberglass tub and got really worried about the damage? Don’t stress out yourself over this problem as it has an easy peasy solution!

Hairline cracks are common in fiberglass tubs because of their manufacturing nature. As a solution, multiple companies and plumbing networks have fiberglass repairing kits. These contain sandpapers, epoxy, sealer, fiberglass filler, and a cloth to conceal the damage and make it as good as before. 

Let us learn about fiberglass tubs and identify the causes of these cracks. Simultaneously, formulate precautionary ways to avoid such damage in the future. 

What Is a Fiberglass Tub? 

Fiberglass, also known as fiberglass reinforced plastic (FRP), is a common material used for making bathtubs. The fiberglass is molded and formed into a glass tub. Over it comes a layer of gel coat resin for the final touches. 

When buying a proper bathtub for your bathroom, it is necessary to know about the commonly used product, which is a fiberglass tub, to make better decisions. 

A fiberglass tub is made of molten glass, which is interwoven to form a tub’s shape. The manufacturers coat the surface with a resin gel coat for a finishing look. 

In the market, Fiberglass is one of the cheapest and lightest materials concerning weight. Thus, installing these tubs in your house is easier, as you don’t have to worry about damages due to the low cost. 

However, according to the users, these tubs are porous (absorb water and moisture) and not durable. These features cause the product to deteriorate faster than others. But because it is low in cost and flexible to design options, people commonly use these tubs. 

Things That Can Cause a Crack in the Glass Tub

top view of a cracked bathtub

Fiberglass tubs are flexible and easily bend with weight. If continuous pressure is applied, the product is prone to break. A crack can be formed because heavy products drop in the bathtub. Other reasons are lack of support and abrasive cleaners.

While talking about things that can cause a crack in your fiberglass tub, it is necessary to classify the causes according to the type of damage created. There are two types of damage: Stress and Hairline cracks. 

Stress cracks are caused when a heavy object hits the tub with immense pressure and causes a big crack that is easier to fix. While the hairline cracks are a result of consistent pressure and abuse of material. They begin to appear on the surface of the bathtub as small cracks which can be repaired over time.

Let us learn about these causes in detail below:

Heavy Objects

There are a lot of people who decorate their tubs with beautiful candles, small plants, shower caddies, and other accessories. At times, these objects hit the tub and knock it down, causing a stress crack in the tub. 

Abrasive Cleaners

Bathtubs can get dirty and nasty, and they do not come off with a gentle scrub. As a result, users sometimes use bleach and ammonia-based commercial cleaners made up of harsh chemicals. Users utilize them to clean their tubs but end up creating small hairline cracks at the base of the tub. 

Lack of Support

While installing a fiberglass tub, people ignore the necessity of providing proper support. Due to this, the weight of the water and your body damage the tub and creates cracks. 

How Much Weight Can a Fiberglass Tub Hold?

A fiberglass bathtub that can accommodate 54 gallons of water can sustain a weight of around 450 pounds or 205 kgs. 

The fiberglass tubs are made of lightweight and brittle materials as compared to other bathtubs. As a result, their weight-bearing ability is different. When a fiberglass tub is compared with other products like acrylic tubs and plastic tubs, there is a significant difference in their weight endurability

An acrylic tub can hold around 40-80 gallons of water weighing 333-667 pounds. Some tubs can carry 1000 gallons of water as well. But fiberglass tubs have lower sustainability in carrying huge weights. 

How Do You Know if Your Tub Is Fiberglass?

If you want to identify whether your tub is made up of fiberglass, you can use ways like checking for faded colors, cracks and scratches, flexibility, and other features in your tub. If it has these characteristics, it is made up of fiberglass. 

There are a lot of times when people are not aware of the type of materials used in their bathtubs. Learn different tricks or short steps to identify your tubs:

  1. The fiberglass tubs fade over time. If you find the base of the product discolored when compared to the top, you are definitely using a fiberglass tub.
  2. When you push your tub, does it flex slightly under pressure? It is another sign of fiberglass tubs.
  3. Hold a magnet near the surface. If it sticks, it is a metallic tub. If not, it is a fiberglass one. 

Can a Cracked Fiberglass Tub Be Repaired and Made as a New Tub?

Yes. As the fiberglass tubs are prone to small cracks and damages, manufacturers have formulated ways to repair them and provide a new finish. 

If you have a fiberglass tub at your place and notice small cracks and leakages around its surface and base, don’t worry. People have designed advanced chemical solutions like epoxy, flex seal, and other related sealing products to mend stress and hairline cracks in your fiberglass tubs. 

Steps You Can Use to Mend a Hairline Crack in Your Fiberglass Tub

before and after bathtub crack repaired

To repair the crack, you need to clean the adjoining surface and apply an adhesive solution and fiberglass fillers. Smooth out the surface with sandpaper and use epoxy and fiberglass cloth to cover the crack. Finally, use a sealer to completely fill the crack

#1 Clean and Dry the Crack

Starting up with cleaning, use a household cleaning solution to clean the surface of the tub near the crack. You should remove the dirt, debris, and other molds around the cracks with the help of a scrubbing sponge. After this, dry the area with a cloth rag. 

#2 Use Sandpaper

After you clean the tub, use sandpaper to give a rough texture to the cracked surface. This will make the repair easier and more efficient. After you are done sanding the area, brush the shavings with a cloth.

#3 Prepare and Apply Adhesive Solution

Prepare the adhesive according to the instructions mentioned on the container. Apply the solution to the crack in a way that covers the whole damaged area. Make sure that the bonding material is applied deep inside the gap.

#4 Put on Fiberglass Filler

Once the adhesive dries, use a putty knife to apply a layer of fiberglass filler to the crack. Do not use excessive filler solution as it will not be effective while repairing the damage. 

#5 Sand and Apply Epoxy

To level up the surface, use sandpaper. After this, prepare the epoxy according to the instructions. Then use a brush to apply it over the crack. 

#6 Add Fiberglass Cloth

Put a fiberglass cloth on the area where epoxy is applied. Press it firmly before the solution dries and remove all the air bubbles with the putty knife.

#7 Do the Final Coat

Once the cloth dries, apply more epoxy over it and let it dry. Finally, put on the sealer that will keep the tub protected from water damage. 

For How Long Can a Fiberglass Tub Last?

The regular fiberglass tubs last for 10-20 years with an average shelf life of 15 years. 

Talking particularly about fiberglass tubs, they are made up of light and flexible glass, which is molded into a tub shape. They are durable and last for more than ten years and have an average life of 15 years. 

But people often complain about these tubs as they deteriorate with the use of specific products like abrasive materials and other chemicals. 

When Should You Replace Your Bathtub?

If your tub is worn off, leaks, and doesn’t provide enough utility and satisfaction, you should consider replacing your tub as it is of no use to you. 

At times people struggle while deciding to change their bathtubs. Here are a few pointers that might help clear all the confusion inside your head:

  • If your tub is outdated and the remodeling will cost more than the original price, it is better to go with a new product.
  • Another thing is the leakage. If the damage is easy to cover, you can use the tub for some time. But if it is completely worn off you should buy a new bathtub.
  • Comfort should be the priority. If the existing tub is unable to give you the level of satisfaction you want, you should replace it and get a new one. 

How to Clean Your Glass Tub Without Damaging It?

Avoid using harsh solutions like bleach and Ammonia while washing your bathtubs. They are harmful and deteriorate the quality of the product. Use mild soaps and homemade solutions from vinegar and borax to clean the tub. 

Here is a list of ways to clean your tub without damaging it:

  • Use an electric scrubber to have a quick cleaning routine where you don’t have to put your body under physical strain.
  • There are homemade solutions like vinegar and baking soda, lemon and soda, etc. You can easily find tutorials on how to make these cleaning liquids on youtube. 
  • Dish liquid soaps are also a good choice as they have a mild effect and do not harm the fiberglass tub.
  • Don’t use abrasive chemicals because they are a major reason why your tubs have scratches and cracks.
  • Don’t use bleach-based products as they fade the original color of the tub and make it unappealing.

What Should You Do With Your Old Tub?

If your tub is old and is no longer in use, you can repurpose it and turn it into a planter, outside pond, bench, and a lot more. This recycling activity can be the first stepping stone toward a better and sustainable environment. 

Do you have an old tub that can’t be refurbished or restored? Convert it into the following things through easy DIY tutorials online:

  1. Outdoor bench
  2. Ice chest for an event
  3. Pond to give a serene touch to the garden
  4. Coffee table
  5. Comfortable couch for your living room
  6. Outdoor sofa chair
  7. Colorful planter or your garden


Fiberglass tubs are an inexpensive alternative to other bathtubs used around the globe. This article would have been a valuable read that will help you fix your fiberglass tub and simultaneously clear off other related queries about these tubs. 

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