Does a Hot Tub Have to Sit on Concrete?

Imagine coming home to a bubbling, relaxing hot tub in your backyard. If you are considering investing in a hot tub the first thing you need to consider is where you are going to position it and does a hot tub have to sit on concrete?

No, a hot tub does not have to sit on concrete. Although a concrete slab is the best and strongest base for a hot tub there are alternatives to concrete. Decks, gravel beds and paving can be suitable for a hot tub to sit on. What’s important is the surface is strong enough to take the weight of the tub, water and the occupants. A full spa pool with 1000 liters of water and 4 persons weighs as much as a motor vehicle. So never install a hot tub on a timber deck or balcony that isn’t rated to take the weight. You run the risk of the structure collapsing and endangering people’s lives.

What’s the Best Base for a Hot Tub?

Does a Hot Tub Have to Sit on Concrete?

No.

However, concrete is the best base for a hot tub because it is very strong and durable.

Before purchasing and installing a hot tub you need to select the right position that will take the weight of the hot tub. Don’t forget a hot tub is filled with water and people which weigh a lot. A full spa pool with 4 persons weighs as much as a motor vehicle. So please ensure the base under the tub is solid and will not give way under the weight.

Ask the hot tub supplier for estimates of the total weight of the hot tub with water. Then add on the weight of four persons to give the total estimated weight. You may be surprised at just how much a hot tub weighs.

I recommend to place the hot tub outside on a concrete, paver or solid gravel surface that is level with good drainage and near an outside power supply.

Do not install a hot tub on a raised timber deck or a balcony as those structures will not take the weight and may collapse and endanger people’s lives.

Never install a hot tub on bare ground or grass. The ground will sink unevenly under the weight of the hot tub and cause the tub to become unlevelled. An unevenly supported hot tub can twist, crack or split and leak water.

Alternatives to concrete include:

• Gravel beds that have been compacted and levelled.
• Paver laid over road base, bedding sand or concrete.
• A spa pad that is designed to take the weight of a hot tub.
• A reinforced deck or balcony that has been built to a building engineer’s specification.

Concrete Base for Hot Tub

I recommend to place the hot tub outside on a concrete slab that is level and near an outside power supply.

Important things to know about concrete:

• Concrete must be at least 100mm (4 inches) thick to be strong enough to support the weight of a full hot tub. Slabs less than 100mm tend to crack over time.
• The concrete slab must contain a sheet of steel reinforcing mesh to hold the slab together.
• Concrete is a mixture of gravel, sand, cement and water.
• Concrete cures with a chemical reaction between the cement and water.
• It takes 28 days to fully cure concrete.
• All concrete must be fully cured before any weight is placed on the concrete slab.
• If concrete dries too quickly it will crack or develop stress fractures.
• Keep the concrete damp for the first few days with a hose to prevent it drying out too quickly. Cover the concrete to keep off the sun.
• When concrete has been kept damp and dried slowly it will be much stronger.

How to Prepare the Ground for a Concrete Slab

The preparation of the subsurface is the most important aspect of laying a concrete base for a hot tub. The ground must be properly prepared before concrete is poured otherwise the concrete may develop cracks and other problems. The subsurface must be level, compacted and have adequate drainage to support a concrete slab. If the ground has poor drainage and becomes wet it will move and flex causing cracks in your concrete. The concrete slab may tilt or become uplifted making it unlevelled.

Remove the grass and top soil layer of the ground to expose the natural ground level. If your site contains fill soil you need to dig deeper to reach more solid ground. Do not pour a concrete slab on fill soil as it will move around and develop cracks.

Dig down 75mm (3 inches) so that your 100mm (4 inch) thick concrete slab will be 25mm (1 inch) above the finished ground level. The concrete slab should be slightly above the ground level to allow water runoff and prevent the concrete slab becoming damp.

Level the site and compact the ground with a mechanical compactor. This is a machine with a motor that vibrates a metal compactor plate. Run the machine over the site to thoroughly compact the ground.

Pour a layer of fine drainage gravel about 25mm (1 inch) thick. Smooth the gravel across the site. Your concrete slab will sit on the drainage gravel protected from ground water.

Now you are ready to pour concrete that should last a long time without cracking or moving.

Paver Base for Hot Tub

Pavers are a great option for the base of a hot tub. They are available in a wide range of colors, sizes and finishes. Pavers can be made from clay, concrete or stone. You may already have a paved area in your backyard that you can use to locate the hot tub.

Many people prefer pavers because if you ever have to access electrical, drainage or plumbing under the ground you can simply lift up the pavers. Try that with concrete!

Laying pavers under a hot tub is similar to laying a paver driveway for your motor vehicles. The pavers must be able to handle the weight of the motor vehicle or hot tub.

The ground preparation under the pavers is the most crucial part of the process. Firstly, excavate the ground to remove top soil and the loose surface layer. Next lay down a road base material and mechanically compact it to form a solid base. Lay down paver bedding sand and smooth it over before you lay down the pavers. Finally, sweep jointing sand into the fine gaps between the pavers to hold them in place and finish the job.

Now the pavers are down you can use the site immediately.

No waiting for concrete to cure!

Gravel Base for Hot Tub

Many people simply use gravel underneath their hot tub.

Gravel is the budget-friendly alternative to a concrete slab. However, prepare the ground in the same way as for a concrete slab so the hot tub won’t move or sink.

Wood Deck for Hot Tub

If you have a timber deck and want to position the hot tub on the deck you need to consult with a building engineer. The engineer will determine how to strengthen the deck to support the weight of the hot tub.

Usually for this type of structure you need a building permit from your local council. The permit not only gives you the permission to modify your deck be ensures the deck meets the latest building code. And this is important when you want to sell your house. A home buyer will perform a council permit search and will not purchase a house that has illegal building work.

Another option is to cut a hole in your deck and place the hot tub through the hole on a concrete slab. This is a great option when the height of your hot tub is higher than the height of the deck above the ground. This will usually avoid the need for a building permit.

A building contractor will be able to quote on the deck modifications.

Other Requirements

The spa pool requires power to run the pump and heater so you need to locate it near a power supply outlet. Ensure the outlet is protected and able to be splashed with water.

When using a spa pool there will be some water splashed from the spa on the ground around the spa so ensure you locate it where water will not be a problem. You will want to ensure that there is some type of drain near the hot tub so you can empty the water into a drain.

Hot tubs must be emptied and refilled several times a year so adequate drainage is necessary. You also need to be near a water supply tap to top up or refill the hot tub.

Read our post on How Often Should You Change Your Hot Tub Water

Conclusion

Does a hot tub have to sit on concrete? Not necessarily but concrete is my first choice with pavers second choice.

The most important thing to consider when buying a hot tub is where you are going to locate it and on what surface?  You not only need a solid surface to take the weight of the tub but a power supply, water supply and adequate drainage.

If you have any questions or comments fill out the comments section below and we will get back to you as soon as possible.