The Complete Guide to Concrete Bases for Hot Tubs


Hot tubs can weigh in excess of three tons when full of water and people, which is why you need a base that’s strong enough to support the weight for years to come. My complete guide will explain:

  • The pros and cons of laying a hot tub base
  • When you might want to consider a concrete alternative
  • Requirements and considerations when preparing to lay a concrete slab

Pros and cons of a concrete base

A concrete pad is one of the best and most popular choices for a hot tub base. Most hot tub manufacturers and stores recommend a concrete slab for its strength, durability, low maintenance, and long lifespan.

However, some people dislike concrete for its poor aesthetics and its ability to crack in certain conditions. Because everyone’s circumstances are different, it’s important to select the right base for your needs. Here are the advantages and disadvantages of laying a concrete slab.

Pros

Level – Creating a perfectly flat and level surface is an absolute necessity for all hot tub bases. A level base ensures that the weight of the hot tub is distributed evenly. Cracks can occur in the hot tub shell in areas where there is a lack of support. Creating a level surface is easy to do with a concrete slab.

Drainage – Creating a slight gradient is also easy to do when laying concrete. A slope ensures proper drainage, allowing the water to run off instead of pooling.

Long-lasting – Concrete can last anywhere between 30-100 years when installed correctly. This is likely to be a job you’ll only need to do once in your life.

Durable – Concrete is by far the strongest and most durable base for a hot tub. Concrete is incredibly sturdy and resistant to most natural environments and chemicals.

Cost-effective – Concrete isn’t the cheapest option available, but its long lifespan makes it a great investment that works out to be very economical over time.

Hidden electricals – Another benefit of concrete is that you can run the electrical conduits through the concrete before it’s poured. Setting your hot tub over unsightly cables is more aesthetically pleasing and much safer.

Combine with patio – Many homeowners opt to have the concrete slab poured as part of their existing patio, which retains the look and feel of your beloved backyard.

Cons

Fixed location – Not being able to relocate your spa is one of the biggest drawbacks of laying a permanent concrete slab, so ensure you find the perfect location for your hot tub before you pour.

Cracks – If you live in an area of the country with huge fluctuations in temperature, it can result in cracks forming the concrete. Concrete expands as it heats and contracts as it cools. If the concrete cannot expand or contract, it will likely crack. This is one reason why a concrete slab should be installed away from direct sunlight.

Aesthetics – A concrete slab in the middle of your yard isn’t the most aesthetically pleasing of sights. However, there are solutions such as these attractive interlocking wooden flooring tilesOpens in a new tab. to help it blend in with its surroundings.

Curing – The concrete slab needs 28 days to cure in order to provide maximum strength. You’ll need to factor in this time before the delivery of your new hot tub.

Expensive – Hiring a professional to lay a concrete slab can be pretty costly if you’re not able to do it yourself.

Concrete base alternatives

A hot tub does not have to sit on a concrete base. There are numerous alternatives, such as gravel, decking, pavers, and prefabricated synthetic pads.

Hot tubs can also be installed in the ground by preparing a concrete vault. Each hot tub base has its advantages and disadvantages over concrete.

A concrete base isn’t the right material for everyone. Here are some of the pros and cons of alternative bases.

GravelLaying a gravel base is pretty easy and shouldn’t require hiring a professional. Gravel is inexpensive and great for drainage. It’s also self-leveling, so you don’t have to worry about cracks appearing in your hot tub’s shell.

Decking – Sitting a hot tub on a wooden decking certainly looks the part. The downside is that hiring a professional to build a deck is pretty costly. If you already have a wooden deck in place, then it’s likely to require reinforcement so that the deck can support the weight of your new spa.

Pavers – Designing your own layout using pavers of different colors, shapes, and sizes is both aesthetically please and inexpensive. Better still if you can place your new spa on an existing patio. However, pavers are prone to sinking due to the immense weight of a hot tub. Ensure that the ground is level and that there’s even support to prevent damaging your spa.

Synthetic pads – These are interlocking squares of 2-inch plastic that have been specially designed to support the full weight of a hot tub. Several benefits of synthetic pads include good drainage, low cost, and portability. However, they should only be used temporarily in situations where a permanent fixture isn’t possible.

Concrete pad requirements: Preparing for your concrete base

Before you can get to work laying your new concrete slab, there are several things you must take into consideration:

  • Pad dimensions, thickness, and slope
  • Selecting the right concrete mix
  • Cost: DIY vs professional
  • Curing conditions and time
  • How to find the right location

Pad dimensions, thickness, and gradient

There are three fundamentals you need to get right when you lay a concrete slab to avoid issues such as cracking and pooling water.

Pad dimensions

The concrete pad’s dimensions should be at least the size of the spa. Most concrete slabs typically measure 8 feet by 8 feet. However, if you own a large hot tub, you’ll likely need to pour a slab that’s 10 feet by 10 feet.

Thickness

A solid cement slab that can safely support a fully-loaded hot tub must be no less than four inches thick. For maximum strength, I recommend a depth of six inches.

Do not excavate the ground deeper than six inches as the concrete slab requires the soil beneath to be solid enough to ensure stability.

Make sure that the surrounding area has been completely cleared of any bushes or trees. This is to ensure that there are no roots growing beneath the concrete, which could cause significant problems later on.

Gradient

The concrete slab should slope 2/3 inch per 10 feet (15mm per 3m). This gradient is to allow the water to run off, preventing pooling beneath the hot tub.

Selecting the right concrete mix

The ideal concrete mix should be a ready-mix that’s crack-resistant and has a compression strength of 4000 PSI.

I recommend QUIKRETE ProFinish Crack Resistant Concrete MixOpens in a new tab. as it meets all these requirements. Some of the benefits include:

  • Significantly reduced cracking from drying shrinkage
  • Air entrainment for improved freeze-thaw durability
  • Eliminates the need for wire mesh in typical slab-on-grade applications
  • Greater impact resistance
  • Superior workability

Cost

The price to lay a concrete slab is going to vary significantly depending on whether it’s something you can do yourself or whether you need to hire a contractor.

DIY

Here is a concrete quantity and cost comparison of laying a concrete slab yourself. The total price is based on each 80-lbs (32.6kg) bag of concrete costing $6.17 in 2022.

DimensionsPoundsKilogramsNo. 80-lbs bagsPrice
8′ × 8′ × 4″2,8371,28736$223
8′ × 8′ × 6″4,2561,93054$334
10′ × 10′ × 4″4,4332,010.556$346
10′ × 10′ × 6″6,6503,01684$519

You can use this handy calculatorOpens in a new tab. to work out exactly how much concrete mix you’ll need for your project.

Note: An 80-lbs (36.2 kg) bag yields approximately 0.60 cubic feet (17 L).

Professional

According to HomeAdvisor.com, a concrete slab typically costs between $4 and $8 per square footOpens in a new tab. ($6 on average), including materials and labor. For an 8-foot by 8-foot slab that’s 6 inches deep, this works out to $1,440. For a 10-foot by 10-foot slab that’s 6 inches deep, the cost is $1,800.

Here is a cost comparison for hiring a professional to lay a concrete slab based on the data compiled by Home Advisor.

DimensionsAverage priceLowest priceHighest price
8′ × 8′ × 6″$1,440$960$1,915
10′ × 10′ × 6″$1,800$1,200$2,400

Unless you know you’re capable of laying a concrete foundation, I think it’s worth the cost to have it professionally laid for peace of mind.

Curing conditions and time

Curing is one of the most important steps when laying a concrete slab. Failure to cure properly can ruin all your hard work as the concrete’s strength and durability will be significantly compromised.

To ensure the concrete has adequate hydration for proper curing, the ideal weather conditions are ample moisture with moderate temperatures and wind.

If the weather is too hot, dry, or windy, the increased water evaporation hinders the hydration reaction, which can result in cracking and other issues. If the temperature is too cold, the hydration process is slowed considerably.

The Concrete Construction website states that, in order to achieve optimum strength, concrete should be cured at 55°FOpens in a new tab. (13°C) for the first 28 days.

Of course, maintaining the perfect conditions is impossible. But ensure that the concrete is cured in moderate temperatures between 50-90°F (10-32°C) for a full month before installing your new hot tub.

It’s best to have the concrete base cured before delivery so that the hot tub can be put into its final resting place upon delivery. Attempting to move a hot tub after delivery is going to be difficult.

How to find the right location

Shade – Do not place your hot tub in direct sunlight. Although it might sound pleasant, the intense heat can be pretty uncomfortable when you’re trying to relax and can cause cracks in the concrete. The sun’s UV rays also burn up the sanitizing chlorine in your spa, meaning you’ll have to balance the water more often.

Distance – Try to keep your hot tub as close to your home as possible. Studies show that the nearer a hot tub is, the more use it gets. Think about having to traipse across your yard after a nice warm soak on a cold winter evening.

Electrical – The further away your hot tub is from the main breaker box, the more expensive it’ll be to wire it in. For safety, hard-sided hot tubs need to be connected to a ground fault circuit interrupter. You must never use an extension cord with your hot tub.

Water source – Try to keep your hot tub as close to a water source as possible. You’re going to have to drain the water every three months and perhaps perform regular top-ups between times. Again, the closer the water, the more likely you are to keep up with the routine.

Drainage – Locating your spa near your private sanitary sewer system makes life easier when it comes to emptying dirty spa water. Draining spa water onto your lawn is possible as long as you follow certain steps.

Access – Ensure that you have access to all sides of your hot tub that have serviceable equipment so that you can remove the panels when necessary. If you’re planning on installing a cover with a lifter, you’ll also need to factor in adequate clearance space.

Privacy – The last thing you want while trying to relax is to have your neighbors peering through a window at you. Installing a fence or planting a wall of greenery around your spa not only provides privacy but also helps to absorb sound.

Delivery – Take measurements to ensure that your hot tub has enough room to get through on the day of delivery. If access to the backyard is impossible, you’ll have to pay for the hot tub to be lifted over by crane, which will set you back a few hundred dollars.

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