Spacers and chairs
The correct cover to the reinforcement is normally created by spacers placed to keep the reinforcement a set distance (cover) from the formwork surface during construction. It is important that sufficient spacers are used to maintain the correct cover and ensure that the bars remain in place during concrete placing and compaction.
Plastic spacers are made to fit particular bar sizes and give specified depths of cover. Small mortar blocks may be used, but it is important that they should be of good quality; generally they should be bought in and not made on site.
Steel spacers are available in the form of stools or continuous chairs. They are suitable for large areas, such as floors, but must have a protective coating when the structure is in a corrosive environment.
British Standard BS 7973:2001 ´Spacers and chairs for steel reinforcement and their specification´ is published in two parts;
Part 1: Product performance requirements
Part 2. Fixing and application of spacers and chairs and tying of reinforcement.