The reduction to the tensile failure stress caused by high-temperature incineration of basalt fibres is investigated. The failure stress of single basalt fibres and tows decreases rapidly with increasing temperature when heated above 250 A degrees C, and at temperatures typically used for incineration of waste composite materials (450-600 A degrees C) the fibre strength is reduced by more than 65%. Strength testing of single basalt fibres with sub-micron notches produced by focussed ion beam milling indicates the reduction in fracture stress is caused by thermally activated surface flaw growth. Following thermal treatment, the recycled basalt fibres were used to produce polymer matrix laminates. The tensile failure stress of laminates containing recycled basalt fibres was much lower than the original strength due to fibre weakening and the absence of fibre sizing needed to promote bonding to the polymer matrix.