Cover blocks are placed to prevent the steel rods from getting exposed to the atmosphere and to place and fix the reinforcements as per the design drawings. Once the steel is exposed to the atmosphere, corrosion starts. Sometimes it is seen that the cover gets misplaced during the concreting activity. To prevent this, tying of cover with steel bas using thin steel wires called binding wires is recommended. Covers should be made of cement – sand mortar (1:3).
Ideally, cover should have strength similar tot he surrounding concrete, with the least perimeter so that chances of penetration of water through periphery is minimized. Provision of minimum covers as per the Indian Standards for durability of the whole structure should be ensured.
Shape of the cover blocks could be cubical or cylindrical. Normally, cubical cover blocks are used. As a thumb rule, minimum cover of 2 inch in footings, 1.5 inch in columns and 1 inch for other structures may be ensured.