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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27 comments on “4 Most Commonly Used Foundation Types For an Inflatable Spa”

  1. Hi there!
    Ihave just purchased an inflatable hot tub and unfortunately... I live on a sand dune! My entire garden is sandy foundations with the odd clump of grass scattered. I would ideally like to place it outside BUT with a sand foundation and a rental house... I don't think this is an option (unless you have an insight?). HOWEVER, I do have a large garage but I am concerned about ventilation and also the garage is sued as a workshop which is less than ideal for a clear hot tub. I am a bit lost and stuck with what to do! Any suggestions?

  2. Like the previous person in 2020 i have just spent a lot of money on a patio and artificial grass. Mya daughter has bought a Intex 4 person octagon hot tub but both the patio and artificial grass area are sloped. On the grass it is 4cm over the length of the tub and on the patio it is 12 cm. I am looking for something that like the spa is portable and isn't ridiculously expensive. I have looked but there is very little on the web about how to do this can you help please

  3. We want to put this on bare ground (some grass) next to the house, but it's slightly pitched away from the house....not majorly, but enough to cause issue.

    Thinking about boxing it out and putting a layer of sand down, but haven't heard of anyone doing this. Are there any concerns you can think of doing it this way?

  4. If I'm putting an inflatable hot tub on a level concrete patio, do I still need to put something under it?

  5. What can be placed under an inflatable hot tub to stop wooden deck rotting is there a pad like the interlocking one's that are mesh like construction and act like under mattress aerators

  6. Hi, If I have a gravel base, with pallets on top - then decking board, do I need to compact?

  7. Hi. I live in rented accomodation and my landlord has just paid A LOT of money on a brand new rear garden. Unforfunately, he demolished the tiled conservatory where we had our LayZ Spa Miami. We have a lovely new paved area perfect for our hot tub, the problem is though, it isnt level. It slopes at a gentle gradient to allow for drainage. As we dont own the property we cant make any changes to the garden, so im in need of some means to create a level surface for the hot tub to sit on, but ideally be moveable. I was thinking of something like a wooden plinth or platform, fitting together in 4 sections or something like that, but i dont know if it would be strong enough. Ive also looked around the internet for some ideas but cant really find anything that doesnt involve butchering our new garden. Any recommendations?

  8. Hi we've just ordered an inflatable spa for 6 people. We are going to position it on the grass as my patio isn't wise enough. Is it ok to be put on grass or do I need to put some concrete flags down 1st

    1. Hi there! It's okay, but I would use some kind of mat or an old carpet under it to protect from rocks or sticks, just like people do with above ground pools.

    1. Hey! Not sure what hot tub exactly are we talking about, but if it's an inflatable one, I would definitely use some kind of mat between the gravel and the hot tub

  9. Hi can I use concrete paving slabs for inflatable lazy spa ? These are 5cms thick but I'm reading I should have a base which is 4 inches ? Thanks

    1. Hi Pauline! Sorry for the misinformation, we've fixed it. The 5cm pads will do just fine. While the hot tub can be heavy, the weight is evenly spread out by the water.