A rebar spacer is a small support device — made of plastic, concrete, or sometimes steel — that holds reinforcement bars at the correct position inside formwork before and during a concrete pour. Spacers ensure that the finished concrete element has the right amount of concrete cover over the reinforcement, which is essential for durability and structural performance.
Why Spacers Matter
Reinforcement steel must sit at a precise depth within the concrete. If the bars rest directly on the formwork or shift during pouring, the concrete cover becomes too thin. This exposes the steel to moisture and eventual corrosion, dramatically reducing the lifespan of the structure. Spacers solve this problem by creating a fixed gap between the formwork (or subgrade) and the rebar.
Types of Rebar Spacers
There are several common types, each suited to different situations:
- Plastic clip-on spacers: The most widely used type for slabs and walls. They snap onto the rebar and come in various heights (20 mm, 25 mm, 30 mm, 35 mm, etc.).
- Concrete block spacers: Small precast concrete blocks tied to the rebar with wire. Preferred in aggressive environments because they do not create a path for moisture, unlike some plastic types.
- Steel chairs: Wire supports used mainly for heavier reinforcement in larger structural elements. Common on commercial projects.
- Wheel spacers: Circular plastic spacers that clip onto bars and roll into position. Useful for long runs of rebar.
Application
Spacers are used in every type of reinforced concrete work: floor slabs, foundations, walls, beams, and columns. For DIY builders working on a strip foundation or concrete slab, plastic clip-on spacers are the most practical choice. Place them at intervals of roughly 50-80 cm along each bar, and make sure the spacer height matches the required concrete cover specified in your structural drawings. Always check that the rebar has not shifted after pouring begins.
Related terms
- Concrete cover
- Reinforcement
- Formwork
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