Clay for Canker sore and Fever Blisters. Clay is excellent for healing mouth sores. Swish with liquid clay 2-3 times a day. Brush your teeth a little hydrated clay on top of a little toothpaste. For bleeding gums and mouth ulcers put the dry powder clay between the cheek and gums. Saliva will cause it to adhere to the area. Sleep with it in the mouth as needed.