What Is Pool Forming?

Pool forming is the process of building a temporary structure that shapes the walls, steps, and features of your pool while concrete is poured and cured. Think of it like a mold: the forms hold the steel reinforcement in place and give the concrete its final shape until it hardens.

Without solid forming, concrete can shift, sag, or leak through gaps, leaving weak spots or structural defects. This is especially important for pools on sloped yards or hillside properties, where forms carry extra pressure and weight.

Why Proper Pool Forms Are Critical to Your Pool’s Strength

When concrete is sprayed or poured, it’s incredibly heavy. If the forms aren’t installed or braced correctly, they can bend, crack, or even collapse, leaving you with a major cleanup and the need to start over from scratch.

Poorly secured forms can also allow steel reinforcement to shift during vibration from shotcrete. That leads to hollow spaces, known as honeycombs, which weaken the structure and shorten the pool’s lifespan.

Bottom line: Strong, well-built forms aren’t an option; they are one of the most critical steps in ensuring your pool is safe and built to last.

Types of Pool Forming Materials: Wood vs. Aluminum vs. Plastic

Builders use various materials for pool forming, each with its own pros and cons.

Wood Forms (Most Common and Flexible)

• Advantages:
  
  
  • Easy to cut, shape, and adjust on-site, especially when freeform shapes like round spas need to be built

• • Ideal for custom features like steps, benches, or irregular pool shapes

• • Readily available and cost-effective

• Drawbacks:
  
  
  • Can swell, warp, or degrade in humid/wet environments if the wrong type of wood is used

• • Requires the right lumber grade to avoid collapse
  • Bracing the wood properly is often overlooked, and it can also help avoid costly mistakes.

Wood remains the top choice for most builders because it allows full customization. Unlike prefabricated aluminum or plastic forms, wood can be cut and braced to fit virtually any design.

Aluminum Forms

• Advantages:
  
  
  • Strong, lightweight, and reusable

• • Resistant to moisture and rot
  • Can be used to form floors on different elevations
    
    
• Drawbacks:
  
  
  • Comes in prefabricated sizes, limiting design flexibility

• • Higher upfront cost compared to wood

• • Harder to adjust or modify on-site
  • Need storage location

Aluminum forms are often used for larger commercial projects or when speed and reuse are priorities, but they’re not ideal for pools with custom features.

Plastic / Composite Forms

• Advantages:
  
  
  • Lightweight and easy to transport
    
    
  • Resistant to rot and swelling in wet climates
    
    
• Drawbacks:
  
  
  • Typically limited to standard pool shapes.
    
    
  • Less durable under high concrete pressure compared to wood or aluminum

Plastic or composite forms can make sense in very humid climates where wood deteriorates quickly, but they don’t offer the same flexibility for custom builds.

Which Plywood Is Best for Pool Forming?

Not all wood is created equal. For pool forming, plywood is typically the best option, but the type you choose matters.

• Hardwood Plywood: Made from birch, maple, or oak. Strong, durable, and smoot,h but usually more expensive.
• Softwood Plywood: Made from pine. More affordable, suitable for structural use, but less decorative.
• Marine Plywood: The best choice for pools. Built with waterproof glue and durable veneers, it resists rot and swelling in high-moisture environments.
• Exterior Plywood (CDX): A general-purpose option that holds up against some moisture but not as long-lasting as marine grade.

Plywood Grades to Know

• Grade A: Smooth, sanded, with minimal defects.
• Grade B: Sanded, with minor repairs or knots.

For pool forming, structural strength is more important than appearance. That’s why marine-grade plywood is often the best investment for safety and durability.

How to Prevent Pool Forms from Collapsing

Even with the right material, installation is critical. Poorly braced forms can collapse under the sheer weight of concrete. Imagine baking a cake: if the pan is flimsy, everything spills over and creates a mess.

To prevent collapse:

• Use the right lumber grade (preferably marine plywood)
• Ensure forms are braced and secured to handle vibration during concrete spraying.
• Double-check that the steel reinforcement is tied firmly to the forms.
• Hire experienced builders who understand slope and soil pressure challenges.

A small mistake here can cost thousands in lost material, labor, and time, making form quality one of the most essential investments in your pool.

Build Your Pool on a Strong Foundation

At the end of the day, your pool is only as strong as the forms that shape it. Choosing the wrong material or setting it up incorrectly can lead to collapses, honeycombs, and thousands of dollars in wasted materials.

The good news is, by understanding the role of pool forming and the strengths of wood versus alternative materials, you’re now in a position to avoid these costly mistakes. Remember: wood, especially plywood, remains the most versatile option for both standard and custom pool designs, such as steps and benches.

Your next step? Talk with your pool builder about which form material they recommend for your soil and slope conditions, and don’t be afraid to ask how they’ll secure the forms against collapse.

Ready to take the next step? Contact us today for a pool design consultation and get expert guidance on building a pool that’s safe, durable, and customized to your vision.