Cement bonds and hardens in the presence of water. Therefore careful storage is imperative to avoid moisture reaching cement before use. The bags of cement should be stored in a closely packed pile, no more than ten bags high. The pile should be on a raised platform in a room with little air circulation. In rooms with open windows and doors, the pile should be covered with plastic sheeting. The same applies if the cement has to be stored outdoors. The platform must be made in such a way that moisture from the ground cannot affect the cement and the plastic sheeting has to be tied so that the wind cannot blow it away and rainwater does not affect the cement. As bagged cement ages and absorbs moisture from the air, it becomes lumpy. If lumpy cement is to be used, its proportion should be increased by half and bigger lumps be removed before mixing.