The mine prop headboard (10) is used to support an inflatable grout bag (44) and is located transversely on an end of an elongate mine prop (12) which is in use installed upright between a hanging wall and a footwall in a mine working. The headboard includes a chock assembly which is composed of parallel, elongate timber chocks (14). A steel reinforcement sheet is secured to and extends over the support surface of the chock assembly to provide tensile reinforcement a grout bag is placed on the headboard and is inflated with grout under pressure sufficient to apply a compressive axial force to the prop between the hanging wall and the footwall.