Hot Tub Shell Bubbling: What Causes It and How to Fix It

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If your hot tub shell is bubbling or blistering, you're not alone. This is a rare but alarming issue for many hot tub owners that can actually be caused by a variety of different factors.

In this blog post, we'll explore what causes a hot tub shell to blister, and some ideas for how to fix it. Plus, we'll provide some tips for avoiding the blisters coming back in future.

So, if notice bubbles appearing on your hot tub shell, read on for information on how to troubleshoot the issue.

What are hot tub shell blisters?

Acrylic hot tubs consist of a colored acrylic skin that is heated and vacuumed over a fiberglass shell. Blisters on an spa shell are caused by water getting under the acrylic material that coats the shell. The water reacts with the components of the shell, creating pressure, and causing the acrylic to expand and form a bubble.

Hot tub blisters come in all shapes and sizes. Some are as small as a dime, while others can be larger than a plate. The average hot tub blister is about the size of an egg.

While they may not look great, small blisters on a spa shell are more of an aesthetic issue than anything else. They usually appear in the corners or the footwell, so you can’t really see them unless your hot tub is empty. And these little guys don't affect structural integrity or usability—when the spa is full, they're usually not noticeable at all.

However, may people prefer to repair them. Thankfully it's not too difficult to do (more on that in a second).

How to identify blisters on your spa shell

Fortunately, blisters are relatively easy to identify:

  1. First, run your finger along the edge of the floor; if you feel any raised or uneven spots, this could be a blister.
  2. Next, check the seat back corners; these are typically where the acrylic is pulled the thinnest and blisters are most likely to form.

If you see any bulges or ripples in these areas, it's likely a blister.

What is causing the blisters in your spa?

There are a few different questions to ask when troubleshooting why your spa shell is developing bubbling or blisters.

How old is the spa?

Blisters are more common on newer spas, and are likely a result of a defect in the manufacturing process. As a spa ages, blister formation declines. This means that the older the spa, the more likely that some type of outside influence created the blister(s).

Blisters are more likely to form on newer spas, and in this case it is most likely a result of defects during manufacturing. In older spas, blisters become less common, but they are more likely to be due to external factors. Sunlight, freezing temperatures, and harsh chemicals are just a few of the common contributing causes.

If you have recently installed a new spa and notice blisters forming, it is important to contact the manufacturer first so they can determine if there is a problem with the unit.

In many cases, the manufacturer will either repair or replace the entire spa—so always check to see if you are covered by a warranty before attempting repairs yourself.

However, if your spa is older and blisters are starting to form, there are other steps you can take to help prevent further damage.

Are you keeping the spa covered when not in use?

When not in use, it is advisable to keep your spa covered. This will protect it from UV rays and other weather conditions—and helps prevent several types of problems, including blisters. A well-fitting spa cover with good insulation will also help to maintain proper water chemistry.

In addition, acrylic spas should always be kept out of direct sunlight to avoid cracking of the surface.

Are you using the right chemicals?

Different types and brands of chemicals will react differently in spa water. Also, mixing brands can sometimes lead to problems. Only chemicals designed and recommended for spa use should be used.

Check with the chemical manufacturer or your spa dealer for guidance on proper chemical use.

Various factors such as the size of the spa, the frequency of use, the number of people using the spa, and the climate will affect how often chemicals need to be added to the water. The amount of time that people spend in the spa will also affect how often chemicals need to be added.

It is important to test the water regularly and add chemicals as needed to maintain a healthy balance. Too much or too little of any one chemical can cause problems. Chemicals should always be added to the spa according to manufacturers' directions.

Always store all chemicals in a cool, dry place out of reach of children and pets.

Is your spa water chemistry properly balanced?

Maintaining the proper chemical balance in your spa is essential to ensuring a safe and enjoyable experience for all users.

Over-use or misuse of chemicals can cause a variety of problems, ranging from skin irritation to more serious health concerns. What's more, the use of non-recommended products can also lead to issues for your spa such as shell blisters.

Luckily, most pool supply retail stores offer water analysis assistance, so you can be sure that you're using the right products in the right quantities.

It's important to never let tablet chemicals set on the surface for extended periods of time. Instead, use floating dispensers to distribute these chemicals evenly throughout the spa.

By following these simple tips, you can help ensure that your spa water chemistry is properly maintained.

I also have a free printable hot tub maintenance schedule which you can download to remind you of exactly what to do.

How to fix spa shell blisters

If you've found blisters on your spa shell and it's definitely out of warranty, there is a DIY method for repairing them, which some spa owners have had success with:

  1. Prepare the surface by using a rotary tool to cut and then sand off the blistered shell. The goal is to get it smooth with no sharp edges.
  2. Apply Marine-Tex epoxy putty according to the manufacturer's instructions. You'll want to wear gloves and old clothes as this can get messy.
  3. Once it is cured, sand down any ridges until you have a smooth surface that will be comfortable to sit on.

A word of warning: this type of repair is not pretty. If your spa shell is any color other than white, the repaired patches will be quite obvious. However, it should cover the hole and prevent further leaks or blistering.

Final thoughts

So, if you're seeing bubbles or blisters on your hot tub shell, don't panic. There are a few things you can do to troubleshoot the issue and get your hot tub back up and running.

In some cases, blistering may be covered by your warranty. If not, you have an option for DIY repair at home. Finally, using a good quality cover and keeping your water balanced can help to prevent this problem from coming back.

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