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Choosing the Right Substrate for Cast-In-Place Concrete Worktops Choosing the Right Substrate for Cast-In-Place Concrete Worktops

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Choosing the Right Substrate for Cast-In-Place Concrete Worktops

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Choosing the Right Substrate for Cast-In-Place Concrete Worktops
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Choosing the Right Substrate for Cast-In-Place Concrete Worktops

When embarking on a cast-in-place concrete worktop project, one of the most common questions we encounter is about the substrate. The substrate serves as the base layer on which the concrete is poured, and its selection is critical for ensuring the durability and stability of the finished worktop. In this blog post, we’ll explore the best practices for choosing and working with substrates, focusing on why cement board stands out as the top choice.


What is a Substrate in Concrete Worktops?

The substrate is essentially the foundation for your concrete worktop. It supports the wet concrete during the pouring process and remains in place to provide structural stability once the concrete has cured. A good substrate needs to be dimensionally stable, strong, and durable, ensuring that it can handle the weight of the concrete and any additional stresses it may face over time.


Why Cement Board is the Best Substrate

Cement board is our recommended substrate for cast-in-place concrete worktops, and here’s why:


1. Dimensional Stability

• Consistency and Reliability: Cement board maintains its shape and size regardless of changes in temperature and humidity. This dimensional stability is crucial to prevent warping or bending, which could compromise the integrity of the concrete countertop.


2. Durability

• Indoor and Outdoor Use: Cement board doesn’t degrade over time, making it suitable for both indoor and outdoor applications. Its resistance to moisture and environmental factors ensures longevity and minimal maintenance.


3. Structural Strength

• Support During Pouring: Cement board is structurally robust, capable of supporting the weight of wet concrete without bending or flexing. This strength ensures a level surface during the pouring and curing processes, which is vital for achieving a smooth, even finish.


4. Versatility in Design

• Hidden Substrate: When designing your formwork, you can create a lip that conceals the cement board. This allows for a seamless and aesthetically pleasing edge on your finished countertop.


Thickness of the Cement Board

The thickness of the cement board is another important consideration. Typically, a thickness of 6mm or 12mm board is recommended. This range provides adequate strength and support while being manageable to work with. Thicker boards offer more robustness but may be heavier and harder to handle, especially in larger installations.


Keeping the Substrate in Place

One of the advantages of using cement board is that it can stay in place after the concrete has cured. This permanence simplifies the construction process and ensures ongoing support for the concrete worktop. The cement board’s compatibility with concrete means it will not react adversely or degrade over time.


How to Install Cement Board as a Substrate


1. Preparation

• Measure and cut the cement board to fit the dimensions of your countertop area.
• Ensure the supporting framework beneath the cement board is level and securely attached.


2. Installation

• Lay the cement board on the supporting framework, ensuring it is level and stable.
• Secure the cement board with screws, ensuring they are flush with the surface to avoid interfering with the concrete pour.

3. Formwork and Pouring

• Build your formwork around the edges of the cement board, creating a lip if desired to hide the board.

Prime the cement board so that is doesn't suck moisture out of the mix.
• Pour the concrete onto the cement board, spreading it evenly and working it into the formwork to achieve the desired thickness and finish.

4. Curing and Finishing

• Allow the concrete to cure as per the mix instructions.
• Once cured, remove the formwork. The cement board will remain hidden beneath the concrete lip, providing continuous support.


Choosing the right substrate is a crucial step in creating a durable and beautiful cast-in-place concrete countertop. Cement board stands out as the best option due to its dimensional stability, durability, structural strength, and ease of installation. By following these guidelines, you can ensure that your concrete countertop project is built on a solid foundation, resulting in a high-quality and long-lasting finish. Whether you’re crafting a kitchen countertop, a bathroom vanity, or an outdoor bar, cement board as a substrate will help you achieve professional and reliable results.
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