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Will Flex Seal Fix a Cracked Bathtub? [ANSWERED]

Cracked bathtubs are a nuisance that nobody wants to deal with. Usually, a severe crack spells doom for your bathtub, forcing you to buy a new one. But can a product like Flex Seal save you time and money by sealing a crack in your bathtub?

Flex Seal has a reputation for doing some surprising and amazing things. But can it work for a cracked bathtub when the risk of water damage to your home is on the line?

In this article, we will answer the Flex Seal question and include other relevant information along the way, such as how to repair and prevent cracks and what causes them to appear in the first place.

Let’s get started.

cracked bathtub
Source: Affordable Bathtub Repair Co

What Causes a Fiberglass Tub to Crack

The most common cause of a cracked fiberglass tub is a heavy object being dropped on it. Of course, your tub can handle light objects like shampoo bottles being dropped on it, but something like a large 10-pound steel plumbers wrench would easily cause a crack.

Besides falling objects, an improper installation can also cause cracks in your bathtub. Your tub needs to be supported to handle the weight of a person.  If the concrete or shims underneath the tub are uneven, your tub can wobble or become unable to handle your weight, causing cracks.

Can You Use Flex Seal to Repair a Cracked Bathtub

Flex Seal creates a watertight bond and will seal a crack in your bathtub. Though Flex Seal is a great product that can seal a cracked bathtub, it should only be used as a temporary solution.

Flex Seal can adhere just fine to fiberglass, but if you have a porcelain or ceramic tub, Flex Seal products do not adhere well to these surfaces and may only seal your crack for a few days.

If you were to use Flex Seal on a fiberglass tub, it might last for a long time, but you should still view it only as a temporary solution because you don’t know when or if the product will give out.

One final note is that Flex Seal is affected by temperature and works best between 60 to 100 degrees. Therefore, the fluctuations in temperature from a hot bath to an empty bath on a cold winter night can affect the seal.

Temporary Fix for a Cracked Bathtub

Water Weld

Water weld works in a similar fashion to Flex Seal by creating a waterproof seal. Water weld is an epoxy putty that can be used on many surfaces, including your bathtub. But where Flex Seal basically works instantly, water weld takes an hour to cure fully—and getting water weld wet before it fully cures can have a negative effect on the watertight seal.

Crack Stabilizing Primer

For small cracks, there are stabilizing primers you can use. Though these stabilizing primers will not fill the crack, they will instead stop the crack from growing. Whenever you have a crack in your bathtub, it’s crucial to fix it as soon as possible because it will grow over time. Stabilizing primer helps buy you some time until you can get a more permanent solution in place.

Repair Kit

Repair kits for your bathtub can usually be found at your local hardware store. Repair kits might be a permanent solution if they are installed correctly and your bathtub is fiberglass or plastic. But repair kits don’t work as well on ceramic or metal bathtubs. Yet repair kits are convenient because they include all the materials you need to get the job done.

How to Repair a Cracked Bathtub

Fiberglass or Epoxy Resin

Fiberglass resin, which is included in repair kits for fiberglass bathtubs, is an effective way to repair this type of bathtub. Epoxy resin works for bathtubs that are not fiberglass. Using resin is messy work and takes some practice. But if you don’t mind getting messy, using resin to repair your bathtub could be a good DIY option.

Foam Insulation

Using polyurethane foam is a great way to create a waterproof seal. The only issue with this repair method is that if the crack is very small, you will have difficulty applying the foam to the inside of your tub. Expanding foam works great underneath your bathtub to give it more support and prevent cracks from ever happening.


If you have a metal bathtub, welding the crack closed would be your best option. Unfortunately, not all of us possess welding skills or welding equipment. So odds are you would have to call in a professional. But a proper weld can make a metal bathtub good as new.

Hire a Professional

Depending on the crack and the type of bathtub you have, some repairs are beyond the skills of your average DIY enthusiast. For example, fiberglass bathtubs are the easiest to repair, and in most cases, you should be able to fix them on your own. But ceramic, porcelain, and metal bathtubs are usually much more challenging to repair and may require professional assistance.

In any case, hiring someone to fix your tub will be less expensive than buying and installing a new one.

How to Prevent Bathtub Cracks

Beware of Wobbling

If you notice your bathtub buckling or wobbling, do not ignore it, these are the type of signs that point to a future crack. As soon as you notice any stability issues using expanding foam underneath your tub can get rid of the problem.

Avoid Powerful Cleaning Products

Many people desire the most potent cleaning products available. But strong cleaning products with harsh abrasive chemicals can weaken your tub’s finish leaving it more susceptible to cracks.

Be Careful

One of the easiest ways to prevent cracks is to take care while in your bath. Don’t throw or smash things and do your best not to drop anything. Also, supervise your children while their in the bath to make sure they do the same.


Can a cracked fiberglass tub be repaired?

Yes, in some extreme cases where the tub has completely cracked in half, you may not be able to repair it. But you can fix most small to medium-sized cracks in a fiberglass tub.

How much does it cost to fix a cracked fiberglass tub?

Less than you think, you will be paying an hourly rate for professional labor plus material costs, and larger cracks will take more time to fix. But generally, you should expect to pay between $100 to $300.

James B. Parker

At a young age, James' father taught him carpentry, and he was pretty much destined for a career in the construction industry. He worked as a professional remodeling contractor for some of the most prominent construction companies for several years, before deciding to pursue his passion for writing.

A vast amount of construction experience allows James to provide practical advice for those considering a bathroom remodel.

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At Loo Academy, our mission is to offer trusted advice for everything related to bathrooms (design ideas, plumbing advice, showering & bathing tips, remodeling guides, and more) — a place where we all spend a great deal of time.

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