Although gravel is a common base for hot tubs, you should not put an inflatable hot tub on gravel directly—especially not on loose gravel. You must construct a frame around it to keep the gravel flat and even, and will need an extra layer of protection to achieve a smooth surface like pavers, or a spa pad.
Let's take a look at why you might choose to put your inflatable spa on gravel, how to do it safely, and then consider some potentially better options.
What are the requirements for an inflatable hot tub base?
Here's what Lay-Z-Spa, one of the leading inflatable spa manufacturers, have to say:
A smooth, flat, even surface that is capable of uniformly supporting the entire filled weight of your Lay-Z-Spa plus the weight of the users.
So, if you're thinking of putting an inflatable hot tub in your backyard, don't just head out and place it on gravel.
Gravel won't provide a smooth surface on its own: a sharp piece of gravel will likely be uncomfortable once you're using your spa, and could even puncture its soft vinyl base.
What are the benefits of a gravel pad for a hot tub?
In general, gravel serves as a good option for an outdoor hot tub base due to its ability to provide proper drainage for any rainwater or overflow from the tub itself.
Plus, unlike concrete, gravel forms a solid foundation that won't crack over time.
It's also relatively easy to install, and generally a pretty affordable option when compared to concrete.
How to use an inflatable spa on gravel safely
1. Build a gravel pad
If you're planning to use gravel, the following steps will give you a rough idea of what's required to build a level and secure gravel pad:
- Choose a site the same size or larger than your hot tub, ideally at the highest point in your yard, and not on too much of a slope
- Dig up the topsoil in the area where you want your hot tub to go
- Build a frame around the perimeter using pressure-treated lumber
- Calculate how many cubic yards of gravel you'll need, accounting for at least 4 inches of gravel
- Pour the gravel into the frame, then level the surface and tamp the gravel to compact it (this will stop it shifting around)
Site Preparations produced a very detailed guide on how to build a gravel base. It's for a shed, but the basic idea is the same:
As you can see, building a gravel foundation is not a small task, and you may feel more comfortable hiring a professional if you really want to go down this route.
2. Add an extra layer on top of the gravel
Once you have your gravel pad ready—or maybe you already had one from a previous hot tub—it's still not a good idea to place an inflatable hot tub directly on it due to the rough surface. It might be fine for sheds or hard-sided hot tubs, but not for inflatable spas.
An insulated ground mat like the CosySpa Floor Protector is a great option. It can help with insulation and minimizing the loss of heat through the base of your spa, as well as adding protection to the bottom from any sharp gravel:
You can also just place another type of standalone hot tub base on top of the gravel pad to provide a protective layer between the gravel and your inflatable tub, like a plastic spa pad.
Alternatives to gravel for an inflatable hot tub base
Unless you already have a gravel base, building one is generally not going to be necessary for an inflatable spa. Let's look at some simpler options.
Pavers are a great option for an inflatable hot tub base.
They are long lasting and very sturdy, plus there's a lot of variety in styles so you can pick some that will perfectly complement the look of your home.
However, be sure to go for smooth pavers that can be interlocked to create a flat, level base for your inflatable spa.
In most cases, you'll want to lay your pavers on top of a level concrete slab. If you don't want the hassle of installing concrete, you can get away with sand plus base panels, or gravel, to provide a sturdy base instead.
Once your pavers are laid, you'll then need to sweep sand in between the joins to secure them in place.
Pre-made spa pad
This option is great if you don't want to tear up your back yard, or are planning to move the hot tub around at some point. It's also generally a lot cheaper than gravel or concrete, and very quick and easy to set up.
Spa pads usually come in several interlocking pieces. They are made from plastic, but strong enough to carry the weight of any hot tub full of water and bathers.
They're also resistant to chemicals and temperature, so no need to worry about overspill from your tub, or leaving them out year-round.
They don't have to be placed on top of gravel or concrete either; you can use a hot tub pad directly on grass or dirt, or to protect your patio or deck—the surface just needs to be level.