Hot Tub Wall Construction – What are the options?

There are several ways you can  go about you hot tub wall construction for your DIY project.. The designs that are available in my store  are compatible with each of the construction methods described below. In this article, we’ll focus specifically on the different types of wall construction you can choose from.

Disclaimer: I’m not a structural engineer. This article is based on practical experience, not formal qualifications. Always consult a professional if you’re unsure about the structural integrity of your build.

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Poured Form Concrete Walls

Poured form construction involves building a wooden mold (also called a formwork) and then filling it with concrete to create the hot tub’s walls and seating.

This method is popular among DIY builders because it allows for a clean, seamless finish and integrated plumbing. However, it does come with some challenges you need to plan for.

Key considerations:

• Bracing is critical. When pouring concrete, the pressure on the formwork is massive. If not properly braced, the walls can bulge or curve, ruining the final shape.
• Use strong timber and multiple supports along the outside of the form to prevent movement while the concrete sets.
• The result is a solid, custom-cast hot tub shape, which is very durable and can be fully tailored to your design.
• One major advantage of this method is that you can embed your plumbing lines and fittings directly into the walls during the pour.
• This often results in a better seal around jets and pipe fittings, which reduces the risk of leaks in the future.

If you’re comfortable working with concrete—or willing to learn—this can be one of the most rewarding construction methods, offering a professional finish and long-term durability.

Concrete Block Cavity

One of the main challenges of building a DIY hot tub or plunge pool is achieving adequate wall strength. A concrete block construction is often considered the easiest method for DIYers, but it comes with specific considerations.

When using concrete blocks, it’s important to incorporate a cavity. This cavity serves three purposes:

• Houses the plumbing
• Allows for insulation
• Contains rebar reinforcement for structural strength

Keep in mind:
This method results in a fairly wide final wall thickness. For example:

• 4” concrete block + 6” cavity + 4” block = 14” minimum total width
• Once you add a capstone, the aesthetic finish can look very polished

Inside this cavity, you’ll place:

• Plumbing lines
• Insulation materials
• Vertical and horizontal rebar

Once everything is in place, the cavity is filled with vibrated concrete to ensure structural stability and eliminate air pockets.

CMU Block

CMU (Concrete Masonry Unit) blocks are the hollow blocks commonly used in general construction. They’re cost-effective, readily available, and provide excellent strength when properly reinforced.

In this method:

• Rebar is inserted through the hollow cores of the blocks, which ties into the poured concrete base and runs vertically through the walls.
• Typically, you’ll reinforce every other core with vertical rebar.
• Optional horizontal ties can also be added to further enhance stability.

Once your block walls are up and rebar is placed, the hollow cores are filled with concrete to complete the structure.

ICF Block

Insulating Concrete Forms (ICF) are interlocking modular units made of rigid thermal insulation. These forms:

• Stack like Lego bricks to form a mold
• Are dry-stacked (no mortar required)
• Are then filled with concrete to create reinforced, insulated walls

Advantages:

• Fast and straightforward construction
• Excellent insulation and structural strength
• Ideal for both in-ground and above-ground designs

Disadvantage:

• Higher cost compared to traditional methods

ICF blocks are a great option if you’re looking for high performance and ease of use, and you’re comfortable with a higher budget.

In ground Cavity

This method is ideal when you’re repurposing an existing hole—for example, replacing a sunken plastic shell hot tub with a more permanent solution.

Here’s how it works:

Here’s how it works:

• Start with a minimum 6” (150mm) cavity around your interior wall space
• This cavity accommodates:
  • Gunite body fixtures (which require space)
  • Insulation
  • Rebar framework
• Once your plumbing and insulation are in place, the cavity is filled with concrete

A 4” concrete block is typically used to form the inner wall. The result is a strong and insulated hot tub structure that integrates smoothly into your existing space.

Which Construction Method Should You Choose?

Ultimately, the right method depends on your personal preference, material availability, skill level, and budget. Each of the construction methods outlined above can lead to a fantastic final result—your dream hot tub brought to life.

That said, every approach comes with its own set of challenges. The best choice is the one that aligns with your location, tools and materials at hand, and how confident you feel taking on the build.

Whatever method you choose, the goal remains the same: creating a reliable, well-insulated, and enjoyable hot tub that stands the test of time.

Enjoy the process—and happy hot tubbin’!

Can I Help You?

If I can help you in any way I would love to hear from you. You can get in touch using the form below.

Thanks - Andi

 

Hi, Andi here. I own Buildahottub.com and also write all of the articles and info pages on the site. Some years back now, I built my own hot tub but struggled to find the information I needed. So, once my tub was complete, I started this website to help others in their own pursuit of hot tub and plunge pools DIY building information.

Fast forward to 2025, I've helped over 1400+ DIY customers just like you all over the world build hot tubs and pools. Have a good look around the site, there are lots of resources here. Please do get in touch if I can help you. - Cheers, Andi