Core Cutting :- A core to be tested for strength shall not be removed from structure until the concrete has become hard enough to permit its removal without disturbing the bond between the mortar and the coarse aggregate. Normally the concrete shall be 14 days old before the specimens are removed. It is preferred the concrete should be 28 days old for drilling cores A core is usually cut by means of a rotary cutting tool with diamond bits. The concrete core drilling machine is portable, but it is heavy and must be firmly supported and braced against the concrete to prevent relative movement which will result in a distorted or broken core, and a water supply is also necessary to lubricate the cutter. Hand-held equipment is available for cores up to 75 mm diameter.