How To Fix Hairline Cracks In Fiberglass Tub?

Fiberglass is renowned for its longevity compared to plastics and ceramics. That is why it is widely used as the core material for bathtubs. But no matter how strong it is, if they are not adequately maintained hairline cracks will most likely emerge.

However hairline cracks on fiberglass tubs can be easily repaired at home. Fiberglass is a versatile product which is comparatively easy to fix than other construction materials.

The Benefits Of A Fiberglass Tub

Down below are some benefits of using a fiberglass tub which you should know about.

  • Fiberglass tubs are famous because they are very lightweight which makes it easier to install.
  • If you want unique shapes and added features like jet, armrest, headrest, drink holder then fiberglass tub should be your first choice. These features can be combined with other materials too, but that will require extra work and extra money.
  • Fiberglass tubs are available in a variety of price range starting from 200 dollars. So you can choose a suitable one according to your budget.
  • check
    These tubs are modern and versatile. You will have plenty of options available to buy from. The maintenance is also cheaper and more accessible than other materials.

Is It Common For A Fiberglass Tub To Crack?

Fiberglass is a kind of fortified plastic, bearing many of the same properties of a plastic. The fiberglass tub is famous for its lightweight and easy installation. It is not prone to damages, and even if it happens most of the flaws are easy to repair at home.

But yes the minor damages are still a factor that ought to be kept in consideration. It is very common for a fiberglass tub to crack because of its porous nature. Upon stressing it by continuously imposing heavy weights and water penetration, hairline cracks form on the surface of the tub.

Such breaks are not severe and can be repaired easily using fiberglass repairing kit.

The Reasons For Hairline Crack

Hairline cracks seem very negligible because of its thin hair-like appearance. But if not treated promptly, the damage can get severe. A hairline crack can appear for various reasons.

The most common reason for a fiberglass tub to crack is weight and pressure. Fiberglass is porous by nature. So continuous exposure to water pairing with the weight problem eventually will weaken the material and cause a hairline crack.

Another responsible factor for this problem is bleach. If bleach or any other chemical application rate is higher than usual, it also causes a hairline crack. Accidental crack can also occur if any heavy object falls on the surface. The durability depends on the user's carefulness as well.

Purchasing Suitable Kit For Fiberglass Tub Repair

Before buying the repair kit, you have to ensure the material of your tub. There are different repair kits available based on the material. If you are intended to fix your fiberglass tub, you have to choose the package accordingly.

  • Make sure the tub is made of fiberglass before you start repairing. You can test that easily; merely tap the surface with your knuckle, wooden spoon or any other material which will not be heavy on the tub.If it is fiberglass, it will produce a hollow, non-metallic sound. The surface will also feel very flexible.
  • Select the closest matching color for the kit you intend to buy. It is comparatively easier to match the standard colors like white, almond, off white. Most of the packages come with a tinting product which can be mixed to get the desired color.
  • Purchasing tools separately can be costlier and time-consuming. Better to look for the kits which come as a package and includes all the necessary tools such as sandpaper, fiberglass cloth, paintbrush, mixing container, stirring utensil, protective gloves, etc.

Hairline Crack Fixing Process

Want to know how to fix the hair line crack? Down below is everything you need to know about the process.


  • Household cleaner
  • Rag or sponge
  • Sandpaper
  • check
    Fiberglass repair kit
  • check
    Paint brush
  • Scissors
  • Fiberglass cloth

The Process 

Follow this process step by step to have a smooth repairing session.

Step 1

Apply your preferred household cleaner on a rug or sponge and clean the damaged area. It is a must to make sure that no stain or dust is left behind. Otherwise, adhesives won't stick properly. Wipe the wet area and let it dry.

Step 2

Sand the area around the cracked line lightly using sandpaper. Brush away the dust.

Step 3

Paint the crack line with the fiberglass adhesive using the brush that comes with the kit. A small paintbrush can also be used. Try to cover the inside of the crack and also adjacent 1 inch to the damaged area. Allow the adhesive to dry completely.

Step 4

When it’s dry, fill the crack with a fiberglass filler using a putty knife. If there is any excess filler coming out of the crack line, scrap it away using the same knife. Let it dry once again.

Step 5

Sand the patched area using sandpaper. Keep sanding until the level of the repaired part matches the surface of the rest of the tub. Brush away the sanding dust.

Step 6

Mix the epoxy gel that comes with the repair kit and paint it on the affected surface using a paintbrush. Apply it on the adjacent surface as well. Then cut a fiberglass cloth according to the size of the painted area and press the fabric on it gently with your hand.

Make sure that it has been placed smoothly and no air bubble has been introduced. Then apply the second coat of epoxy gel on it.

Step 7

In the last step apply the sealer or finish coating that comes with the kit. Brush it on the repaired area and let it dry.

So by following the above mentioned 7 steps, hairline cracks on fiberglass tub can be easily fixed at home with a minimum cost. The fiberglass repair kit is widely available in any hardware shop.

Struggles with Mismatched Patch

It is a sad truth that in most of the cases your repaired area will not precisely match with the rest of the surface. Even if you gain expertise, still it's not possible to make it look completely like before. The main struggle is to match the original color of the tub.

However, if you are too worried about it, you can directly contact the manufacturer of your tub. If you know the brand, then it is not difficult to reach them online. Some of the brands supply one extra can of the same color upon request.


Fiberglass tub serves as a cost-friendly and durable alternative to traditional metal and ceramic tubs. Tubs with too little base support or subject to hulking use might develop cracks over time.

If left unaddressed, the hairline cracks can spread to the side and floor of the tub and ultimately damage the whole tub. As mentioned throughout the article, such cracks can be repaired swiftly at home.

The only trick that you can implement is - whenever you see a crack, immediately go for action no matter how big or how small the crack.

Leave a Comment

This site uses Akismet to reduce spam. Learn how your comment data is processed.