Every part of a building needs a different cover. Cover is the layer of concrete between the steel bars and the outside of the concrete. A cover block keeps this gap the same everywhere.
Common cover sizes
On many sites, people use these sizes for normal conditions:
- Slab: about 20 mm
- Beam: about 25 mm
- Column: about 40 mm
- Footing: about 50 mm
Your building drawing gives the real size for your job. Near the sea, in wet places or for water tanks, the cover is often more. Always follow the drawing and ask your engineer.
Why the size matters
- Too little cover: water reaches the steel faster, and the steel can rust.
- Too much cover: the steel sits too deep, and the slab or beam can lose strength.
Quick tips
- Use concrete cover blocks, not stones or broken bricks.
- Keep blocks at an even gap under the steel.
- Check the cover at a few places before you pour.
Need to know how many blocks you need? Use our free cover block calculator. For prices, see cover blocks price.
