A grout plug 10 for plugging a drill hole 20 in a mine. The plug 10 comprises an elongate sleeve 12 of porous material adapted to be received in a drill hole 20 and a volume of dry grout material 14 in particulate form. The plug 10 also comprises a liner 16 of water-soluble material, the liner 16 being provided within the porous sleeve 12 for containing the grout material 14 within the porous sleeve 12 in its dry form. In use, when the plug 10 is exposed to water the liner 16 dissolves and the water mixes with the grout material 14 to form a slurry which can seep through the porous sleeve 12 when the plug 10 is tamped into the drill hole 20 to block the drill hole 20 when the grout material 14 cures. A related clay plug is also described having a central core of substantially solid material of low permeability which forms a substrate against which the clay material may cure.