When you actually have a REAL problem, you'll know it, because water will start leaking out of the shell. At that point, it's time to drain the spa, let it dry, and patch the crack with a fiberglass repair kit.... the same type used to repair boats and cars, available under the "Bondo" trade name.

How do you know if you've got a reinforced fiberglass shell? If you can see the shell underneath the skirt, and the shell doesn't flex with pressure applied by hand, then it's probably fiberglass reinforced. You can also tell by looking at the lip edge of the shell. Usually on this type of shell, the edge of the shell material will be at least 1/4 to 1/2" thick. Upon close examination, you will be able to see a thin layer (the surface acrylic) and a thick greyish looking layer which is the fiberglass.

Other types of spa shells may not fair so well. Some of them are made with only a thin acrylic layer form, and supported by "full foam insulation". In other words, the foam completely fills the spa cabinet. These shells are pretty fragile and do not have the durability that a fiberglass reinforced shell does.

In this case, getting the cracks to stop cracking any further is extremely important, because once a crack in a shell like this gets more than say 3-4" long, it really loses a lot of its ability to keep from contining to separate, even if patched and repaired.

The best solution with a shell like this is to "hole stop" the crack. Drill a small hole, (approximately 1/16" diameter) at the very tip of the crack.

For short cracks of less than 3", a 1/16" bit should do fine. If more than 3" use a larger bit, preferably a 1/8" diameter. The larger hole allows for more expansion and contraction that a longer crack is likely to endure, without fracturing again.

The round hole will create an area of structural integrity by virtue of its round shape, and it shouldn't crack any further, unless of course, stress is continually induced here, or if the plastic material has aged such that it just won't hold anymore. 

Once the hole is drilled, it's time to fill the crack and hole with any type of a good plastic sealant material, such as "plumbers GOOP", plastic cements that are thick bodied that have "filling" characteristics, and in some instances, even 100% silicone caulk will work. 

Prepare the area for the sealant by cleaning it with denatured alcohol.  Only apply the alcohol in the immediate area of the crack, about 1/2" on either side. Let it dry for about 4 minutes and then apply the sealant over the cleaned area, with an overlap of about 1/8-1/4" on either side of the crack. 

To repair a shell in this manner may take a couple of attempts, including draining, drying, and refilling the spa to test for watertight integrity. But in the end, it's still a lot cheaper than replacing the entire spa, which is usually the only other solution to the problem.

If you have ever repaired a spa shell crack and have discovered other ways of fixing them, please email us here and let us know! We'll try it out and if it works, we'll get your submission included here with this page.... Thanks