Rebar for Hot Tubs and Pool Construction Explained

rebar for hot tubs and plunge pools

Imagine soaking in a steaming hot tub or cooling off in a refreshing pool on a hot summer day. What you might not realize is that beneath the sparkling water lies a crucial element contributing to its strength and longevity: rebar.

Rebar, short for reinforcing steel bar, is a hidden hero in the world of concrete construction, including DIY hot tub and swimming pool builds. It adds vital tensile strength, which concrete lacks, allowing it to withstand the pressure of water and resist cracking.

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Why Rebar Matters

Concrete is fantastic for compression, meaning it can bear weight pushing down on it. However, it’s weak in tension, meaning it can crack or break when pulled apart. This is where rebar comes in.

Studies by the American Concrete Institute (ACI) show that properly placed rebar can significantly increase the tensile strength of concrete structures [ACI source]. In layman’s terms, it acts like a skeleton within the concrete, providing the internal support needed to handle the hydrostatic pressure of water in your pool or hot tub.

Rebar for DIY Projects: Concrete and CMU Blocks

While shotcrete and gunite require specialized equipment and techniques, there’s good news for us DIY enthusiasts. Rebar plays a vital role in both concrete and cmu block construction methods for hot tubs and pools.

  • Concrete Pools: Rebar creates a strong foundation for poured concrete walls and floors. The specific size, spacing, and design of the rebar cage will depend on the pool’s size and depth. However, for most of our hot tub and cocktail pool builds a spacing of 12” center to center is sufficient.

  • Here’s where positioning becomes crucial. For walls, vertical and horizontal rebar should be placed in a grid pattern throughout the concrete, ensuring even distribution of strength. The rebar should be positioned near the center of the concrete wall, typically 2-3 inches away from each edge, to maximize its effectiveness. 

  • CMU Block Pools: CMU blocks are pre-cast concrete blocks that interlock to form the pool’s walls. While they offer some inherent strength, rebar further reinforces the structure, especially along the curves and corners where stress is concentrated. Similar to concrete walls, rebar should be placed horizontally within the block cavities to create a continuous web of reinforcement and vertically through each of the blocks at 12” centres which is quite straight forward on an 8 x 8 x 16 block.

  • Block Cavity Rebar Positioning – if you are using solid blocks, then you may opt for a double skin block cavity construction method. Normally, the plumbing would be housed in the cavity along with the rebar and then concrete filled for strength. One thing to note here is that it is easier to put the plumbing in place FIRST before the rebar so that you can tie in the rebar to the plumbing for support but also so the rebar doesn’t block or get in the way of the plumbing. Again, in general air for 12” center to center but you can make allowances for the plumbing.


Rebar: The Foundation and the Risers

Think of rebar not just as reinforcement within the walls, but also as the base upon which your pool or hot tub structure rests. A properly designed rebar mat should be placed beneath the concrete floor. This mat will be tied to the vertical wall rebar using hooked extensions or stirrups, creating a unified structure that can resist movement and cracking.

Choosing the Right Rebar

Not all rebar is created equal. Here’s a quick guide for DIY projects:

  • Material: Standard steel rebar is sufficient for most residential pools and hot tubs. However, for areas with high chloride content in the water (like near saltwater environments), consider using epoxy-coated rebar for added corrosion resistance.

  • Size and Spacing: Rebar diameter typically ranges from #3 (9.5mm) to #5 (15.9mm) for these projects. Spacing between bars is crucial and should be determined by a structural engineer based on your pool’s size and design.

Rebar Strength: Yield Strength vs. Tensile Strength

There are two main ways to measure the strength of rebar: yield strength and tensile strength.

  • Yield Strength: This is the amount of stress a rebar can withstand before it begins to deform permanently. Think of it as the point where the rebar bends instead of springs back.
  • Tensile Strength: This is the maximum stress a rebar can take before breaking.

The specific yield and tensile strengths of rebar depend on its grade. Rebar grades are designated by a number representing the minimum yield strength in thousands of pounds per square inch (ksi). For instance, Grade 60 rebar has a minimum yield strength of 60 ksi.

Important Note: When discussing rebar in construction projects, yield strength is typically the more relevant value.

Strength of #3 Rebar

Most #3 rebar in the United States is made from Grade 60 steel. According to the American Society for Testing and Materials (ASTM) standards, ASTM A615 [ASTM source], Grade 60 rebar has a minimum yield strength of 60,000 psi.

Grounding and Bonding Your Rebar Grid: An Essential Step for Safety

While rebar provides the structural muscle for your hot tub or pool, it plays another crucial role – safety. Here’s where grounding and bonding come in.  Grounding connects the rebar cage to the pool’s grounding system, which in turn ties into your home’s grounding electrode or you can have a separate one for the pool or hot tub added.

This helps dissipate any stray electrical currents that may leak from equipment, preventing them from energizing the pool structure and potentially causing electrical shock. 

Bonding connects all metal components around the pool or hot tub, including the rebar, plumbing pipes, handrails, and light fixtures, to the grounding system. This creates a uniform potential throughout the metal components, further minimizing the risk of electrical hazards.

Following proper grounding and bonding procedures as outlined in electrical codes (like the National Electrical Code – NEC) is essential for a safe and enjoyable swimming or soaking experience. Remember, consulting a qualified electrician is crucial to ensure your hot tub or pool’s electrical system is up to code and properly grounded.


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Thanks - Andi


Hi, Andi here. I own 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.

Today, I've helped over 1000 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

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