Bob's Pools and Spas

Dear Bob,

We own a large fiberglass hot tub (we don't know the age as it was already here when we bought the house 7 years ago). There is a large crack on the bottom running between two of holes where the air bubbles come out. First of all, what is the best way to patch a crack in fiberglass? Second, do you think water is actually leaking of the hot tub or just going down into the air channel?

Thanks in advance for any help,

First of all this is a very common question when people see cracks. Let me make you feel easier about it right away. 90% of the time they DO NOT LEAK.

The reason for this is due to the way fiberglass hot tubs are made. The inside of the spa is usually not fiberglass at all, it is acrylic. Acrylic is a very hard thin sheet of material that is heated to just the right temperature so it will melt. The melted sheet is then "vacuum formed" into the shape of a spa. It only takes minutes for the acrylic to cool, but when it does it becomes hard again. It is only 1/16" thick and is almost like a giant eggshell. If you dropped it on the floor it would shatter into thousands of pieces. In order to give the shell strength, the shell is turned upside down and several coats of fiberglass are sprayed onto the back. This builds up the material making it very hard and strong. When the fiberglass dries, holes are drilled through the shell for the jets and plumbing. The spa shell is usually 1/4" to 1/2" thick at this point, and will last years.

However, the acrylic is still only 1/16" thick, and is subjected to many extremes while in use over its life. Some common problems are cracks (long or short, sometimes only one and sometimes thousands in one spa), blisters or bubbles (small raised spots on the surface), and cobalt staining (the stains produced from the fiberglass resins behind the acrylic).

All of these problems can be repaired at a cost, but that depends on a lot of factors such as the following.

If there is only one crack that is very noticeable in a new spa, it is probably worth fixing. This would be like a scratch in a new car.

If there are several cracks because the spa is getting old, don't worry about fixing them. You may spend more to repair it than its worth.

If there are blisters, they should only be repaired if they crack open and create a safety hazard where someone could get cut from a sharp edge. Some spas can have 50-100 blisters, but don't need to be repaired because they don't cause a problem other than aesthetics.

So after all that is said, here are your answers:

First, I have never seen a spa that leaked through a crack in the acrylic. Once in 15 years I have seen a crack in the fiberglass that actually caused the acrylic to crack and it leaked. The factory missed a small spot when they applied the fiberglass backing so the acrylic was the only thing preventing a leak and after 10 years, it cracked and the spa started leaking. This is very rare, and other than this one spa out of hundreds I have seen with cracks. it the only one I have seen that actually leaked.

Second, to repair the crack in acrylic, you should drill a very small hole at each end of the crack, only 1/16" of an inch deep.

Be careful, you don't want to drill a hole all the way through the spa shell!!! Only drill the acrylic. If the crack is between two air channel holes, don't worry about drilling the crack. The holes at the ends of the crack will help prevent the crack from getting bigger.

Next, use a waterproof bondo filler or a fiberglass filler found at auto stores. You only need a very small amount, just enough to fill the crack. Sand the area of the crack and a small amount around the repair area smooth with wet dry sand paper.

At this point the crack is gone but the repair will look worse than the original crack! The best acrylic repair companies will strive to match paint a close as possible, and this is the hardest part of the repair. If you have a solid color spa, like white, it's no problem. But if the acrylic has a marble color to it, the color match can be difficult.

A few things to think about..........if it's an older spa and has a crack, what are the odds that another crack will develop somewhere else?

And, with the age of the spa, is it worth the time and energy to repair a cosmetic problem?

My personal opinion is this: If the spa is in great shape and you don't want to see the crack, fix it. If the spa is older and you only use the spa at night with the lights off, don't worry about it! Test the chemicals and jump in.

Thanks, I really appreciate your advice! I went ahead and drained the tub so I could see just how bad the crack had gotten and i have attached a picture just in case it might change your opinion. The crack is worse than I had realized, but from what you tell me I hope the damage is just cosmetic. Thanks again

Chad

WOW!

Thanks for the excellent picture.....

When looking at the photo, at the 9 o'clock position, just above the finger in the picture. Is the acrylic and fiberglass cracked? or just the acrylic?

This is what I would do if this were my spa, and the fiberglass is not broken:

I would remove all the loose pieces of acrylic all the way to the edge of the crack. Be sure to remove all of the acrylic that has seperated from the fiberglass underneath, all the way to the edges of the blister. Examine the fiberglass to be sure that it is not cracked.

Find a couple of dowels that you can stick in the air channel holes. You dont want to fill the holes with the filler material. Apply filler to the area as smooth as possible. Allow the filler to harden somewhat before removing the dowels. when the filler is dry you can sand smooth and paint grey. (Easiest color to match!)

If the fiberglass is broken also, you will need to use a sheet of plastic of some kind with a string to provide backing for the material. The photo looks like the fiberglass is broken, but there are two layers of fiberglass here. After the spa is made and fiberglass is sprayed, they will drill holes through the spa, and cover the backside of the holes with more fiberglass, except there is a pocket created for air to flow into. This is the actual "air channel". The air channel is filled with water except when the blower is on. When the blower is off, water runs back in the channel. This is why in the photo, it appears to be broken all the way through the fiberglass, but the spa is still probably not leaking.

This is a serious repair that you may want to call a professional to do the job. It is also beyond the scope of email directions. I am still at a loss as to how this crack came about. If you had not told me it was seven years old I would think something was dropped on it. It looks like someone dropped a bowling ball in you spa! Has this slowly become worse, or did you buy the house with the spa in this current condition?

[TheSpaGuy] Thanks, Bob.

Table of Contents

Back to Top