What is a spacer?
A spacer (also called a cover block or chair) is a small device that holds reinforcement at the correct distance from the formwork, ensuring the required concrete cover is achieved. Without spacers, the reinforcement would rest against the formwork and be insufficiently protected.
Why are spacers important?
The concrete cover — the layer of concrete between the reinforcement and the outer surface — protects the steel against:
- Corrosion — moisture and oxygen cannot reach the steel
- Fire — the cover insulates the reinforcement during a fire
- Carbonation — the concrete shields the steel from chemical attack
The required cover varies from 20 mm (internal) to 50 mm or more (external, aggressive environments).
Types of spacers
- Plastic clips — the most common type, available in various sizes
- Concrete blocks — small precast concrete cubes or cylinders
- Wheels — plastic wheels clipped onto the reinforcement bar
- Spring clips — metal clips for suspending top reinforcement
- Continuous spacers — plastic strips or rails for supporting mesh reinforcement
Applications
- Floor slabs — spacers beneath the reinforcement mesh ensure the correct cover
- Walls — spacers between inner and outer reinforcement layers keep the mesh in position
- Foundations — spacers are used in pile caps and foundation beams
- Precast — in the factory, spacers are precisely placed for consistent cover
Related terms
- Reinforcement
- Concrete
- Concrete cover
- Formwork
- Rebar
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