How To Repair a Hairline Crack in A Fiberglass Tub

If your fiberglass tub is used frequently, does not have the proper support, or is hit by a heavy object, it is likely to develop hairline cracks with time.

Also, cleaning using harsh materials will wear it out and lead to cracks of some sort. If these cracks are not repaired properly, they will develop into bigger cracks which may even break the bathtub apart. 

You can repair a crack in a fiberglass tub yourself using a fiberglass repair kit, which can cost as little as $50.

If the crack is too big in the tub surround, you may need to get a professional to fix it for you. This will cost between $80 and $150 (sometimes even more). You can always replace your fiberglass tub with a shower.

The other type of crack on your bathtub is a stress crack that is caused by heavy objects damaging the surface but not going deep inside the bathtub. There is also the spider crack which looks like a spider in that there is a hole in the middle then hairline cracks going in different directions.

All these types of fiberglass cracks can be fixed with the guide in the following sections. With the right fiberglass repair kit, you can fix these cracks as soon as they appear to avoid damaging the whole bathtub.

A typical fiberglass repair kit will have the following items:

  • Hardener
  • Colorants
  • Thickener
  • Mixing container
  • Stirring tool
  • Polyester resin
  • Fiberglass mesh
  • Sandpaper in various grits
  • Protective gloves.

Besides the repair kit, you will also need the following items:

  • Paintbrush
  • Sandpaper (fine)
  • Scissors
  • Cleaning sponge
  • Household cleaner

Given that there are chemicals involved in this process, you need to have the proper ventilation in the work area to avoid getting choked. Also, you need chemical-resistant gloves for this job.

Before you begin the repair process, you need to check whether the crack is superficial or has gone all the way to the bottom of the tub. If the case is the latter, you will need the services of an expert. If it is the former, read on.

The Cost Of Fixing A Cracked Bathtub

A professional plumber is likely to charge you between $80 to $150 an hour for such repairs. However, your own kit will only require $50 or less.

How To Repair Cracks In A Fiberglass Bathtub

Here is a step by step guide to repairing the hairline crack on your fiberglass bathtub. Always use the right colorants which match your tub color.


Use the household cleaner and the sponge to clean the area around the crack. Make sure there are no sediments left on it after the cleaning. Afterward, rinse it with water then dry it with a dry piece of cloth.

Pro Tip: at times, ¼ holes are drilled at the end of the crack to stop it from extending further. This ‘stop-drill’ hole should only be attempted when one is a professional and familiar with it.


Take a piece of the sandpaper then slowly sand the area surrounding the crack. With a soft brush, brush away the dust to leave a clean (but slightly rough) area.


Using a soft brush like the one found in the fiberglass repair kit, paint the area with the crack and an inch around it as well.

Apply as much adhesive as possible without using too much of it then let it dry as per the instructions of the repair kit.


Get hold of a putty knife and fill the crack with your fiberglass filler. After that, remove the excess putty by scraping the surface of your tub.

Ensure that, even with the putty, the repair area is still flush with the rest of the surface of your bathtub. Let the putty dry as directed by the repair kit instructions.


Using the fine-grit sandpaper, sand away any excess material from the surface of the crack to ensure the crack and the rest of the surface are flush with each other. Brush away the dust from the crack area.


With the instructions from the repair kit, mix the epoxy gel coat to a good consistency then use a paintbrush to apply it to the cracked area. Ensure the gel covers the whole crack and an inch around it as well.


Before the epoxy gel drys up, cut a piece of fiberglass cloth the size of the area to be covered and place it on the crack using your hand.

To eliminate any air bubbles below this cloth, use your putty knife by running it across the cloth. Ensure the cloth is also flush with the rest of the bathtub surface.

When sure of the look and feel of the cloth, apply a second epoxy gel coat.


As the last stage, apply a coat of sealer to the area of the crack and wait for it to dry. If you have a buffing compound with you, apply it to restore the glossy finish of the tub surface.

If, as per the directives of the repair kit, the sealer is dry enough, you can fill the tub with water and have a bath. However, if your bathtub has too many cracks, or they keep recurring, you need to have it refinished to avoid breaking it apart.

If that does not work as well, consider a new tub. This process also applies to the repair of a bathtub made of acrylic.