4 Most Commonly Used Foundation Types For an Inflatable Spa

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Last updated: 
June 21, 2022
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So you are now prepared to install your portable hot tub. You understand the benefits of having a tub in the house, you have done your research and have found the right choice that you deem perfect for you.

Now you should abide by the following 3 rules of thumb:

  • Your tub must not be close to any power line. Never place your hot tub near an electric outlet
  • The foundation under the hot tub must be very strong
  • The foundation has to be level

These are the 3 most commonly used foundation types for a hot tub:

1. Grass


The grass is definitely one of the most used surfaces under a blow-up hot tub. And why not? If not contaminated with broken glass or wooden sticks, it makes an awesome cushioning material.

However, the ordinary ground is not such a good insulator. Try to use a ground cloth or an air mat under the hot tub, both for heat insulation and puncture protection.

2. Concrete pad

concrete pad

This type of foundation is recommended whether or not your tub is an outdoor one or an indoor one. Your concrete pad must have the following characteristics;

  • It must be level. This is to avoid any kind of settling after you install your tub.
  • The thickness of your concrete pad must be adequate to support the weight of the hot tub. While the hot tubs can be heavy, the weight is evenly spread out by the water. 
  • The size of the pad should be at least the size of the tub.

While the following two characteristics have nothing to do with the construction of the foundation, they are equally important:

  • You should have constructed your concrete and ensured that the concrete would have dried before the delivery of your tub. This is important because you can immediately install your tub and start making use of it right away.
  • If you find any or all of the construction characteristics stated above to be intimidating, you can call on any home improvement service provider in your neighborhood.

3. Crushed gravel or stone

crushed gravel

This type of foundation is recommended especially if your tub is to be situated outside.

This foundation must have the following characteristics;

  • It must have a minimum thickness of 4 inches
  • You must construct a frame around it to keep the foundation perfectly in place
  • it must have a proper channel for drainage so that your tub would be durable

The following recommendation has nothing to do with the foundation but it is also important;

  • Try to install low-level showers around the tub. This is to ensure that you can wash your feet before entering the tub which will prevent dirt in the tub.

4. Ready-made synthetic tub pads

hot tub pads

Check out these pads on Amazon.com

These are recommended for either outdoor or indoor tubs. They have the following advantages over the other types of foundations;

  • There is no need to pour concrete or work out any other thing like that.
  • They are lightweight and less expensive
  • They are quick and easy to set up
  • They require little to no maintenance

Their pieces interlock. This means that…

  • You can easily dismantle the pad if the need arises. For example, in case you want to move out of your present location to another one.
surface to use under hot tub, wooden tiles
Always be careful what’s underneath your hot tub, do not place it directly on surfaces that might damage it!

Stay Away from Slopes

First and foremost, the area on which you place your hot tub needs to be completely flat. If you place it on a surface with even a slight slope, the tub’s structural integrity will be compromised, and it is likely that it will collapse if filled with enough water.

To keep this from happening, pay close attention when you fill the tub. If you notice that water starts to flow more to one side, or if the walls start to bulge in a certain direction, you will need to move the tub to another location.

Firm Surface under the spa

Firm is the Way to Go

In addition to being level, the surface beneath an inflatable hot tub must also be sturdy and firm. Once filled with water, the tub will weigh quite a lot, and this weight will shift around as people get in and out of the tub. You should thus avoid muddy or sandy surfaces that might not provide the support an inflatable tub needs. Opt for placing your tub on the pavement, or a concrete deck.

tile floor

Consider Water Drainage

Water drainage is another important consideration. Splashing will happen when people use the tub, even if it’s unintentional, and you need to be able to deal with spills with minimum fuss. You also wouldn't want to have some difficulty when the time comes to empty the tub. For this reason, it is usually best to keep your tub on a surface where water drains easily.

This usually means setting up your portable hot tub outdoors, but an indoor area that meets this requirement will also be suitable. If you believe your hot tub is leaking check out how to find the leak.

Use a Mat for Additional Protection

Whatever surface you settle on, it is best practice to lay a cloth or ground mat underneath the portable hot tub. In addition to protecting the bottom of the tub, this will also minimize water damage to the surface it is on.

mat under hot tub

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