Bar Chairs in Concrete: Sizes, Spacing, and Standards for Reinforced Construction

What Are Bar Chairs?

Bar chairs are small supports used to position rebar or mesh reinforcement within formwork at the correct depth. They stay embedded in the concrete after pouring and prevent the steel from shifting during placement. This ensures consistent cover, uniform load transfer, and long-term structural integrity.

Types of Bar Chairs and Their Uses

Different types of bar chairs are designed to suit specific construction needs:

Plastic Clip-On Chairs:
The most common type for slabs and footings. They're lightweight, durable, and resist corrosion.

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Concrete Bar Chairs:
Used in fire-rated or exposed structures where non-combustibility is required.

Metal Bar Chairs:
Provide maximum strength and stability for high-load or precast applications.

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Combination/Top-Deck Chairs:
Used for top layers of reinforcement or dual-height configurations.

For reliable reinforcement support, explore Form Direct's Bar Chairs - Accessories.

Understanding Bar Chair Sizes

Bar chair sizes refer to the height of support they provide to reinforcement. Dual measurements like 50/65mm or 75/90mm indicate two usable heights, depending on which side is placed down. For example, a 50/65mm chair provides either 50mm or 65mm cover depending on orientation. Choosing the right height for your bar chair also ensures proper cover and compliance with AS 3600:2018 durability requirements.

Bar Chair Spacing: How Far Apart Should They Be?

Proper spacing ensures even load distribution and prevents reinforcement from sagging during the pour. As a general rule:

• One chair per square metre for standard mesh reinforcement.
• Closer spacing (0.8m or less) for thicker slabs or heavy rebar.
• Edge and corner reinforcement may require additional chairs to prevent movement.

Compliance and Australian Standards

Incorrect spacing or undersized chairs can result in reinforcement drifting off-cover, leading to cracking, reduced durability and failed inspections. To remain compliant:

• Use chairs tested to AS/NZS 2425:2015.
• Follow cover requirements in AS 3600:2018.
• Refer to NCC provisions for residential slabs and footings.
• Ensure all chairs used match the reinforcement plan and engineering drawings.

Need Reinforcing Accessories That Meet Australian Standards?

Bar chairs play a critical role in maintaining correct reinforcement cover and ensuring compliance with Australian building standards. Choosing the right type, size, and spacing supports structural performance, prevents premature deterioration and ensures the pour meets durability requirements.

Form Direct supplies a full range of compliant bar chairs, deck rails and reinforcing accessories for residential, commercial and industrial projects.

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FAQs

What are bar chairs in concrete?

Supports that hold reinforcing bars or mesh at the correct level within formwork before and during concrete pouring.

Do bar chairs stay in the concrete after pouring?

Yes, they remain in place permanently to maintain reinforcement position and cover.

What size bar chairs should I use for a 150mm slab?

Typically, 65–75mm bar chairs provide the right cover for 150mm slabs, depending on project design.

How many bar chairs per square metre do I need?

One per m² is standard for mesh slabs, but closer spacing may be required for heavy rebar.

What is AS/NZS 2425:2015?

An Australian standard specifying the requirements and testing procedures for bar chairs used in reinforced concrete structures.