The invention generally relates to compositions and methods for promoting hemostasis and sealing a wound by producing an adhesive cast. In particular, the invention provides compositions comprising clay minerals with specified particle sizes, which, when applied to a bleeding area, allow for a desired result in at least one of the following activities: stopping blood flow from a wound, forming a cohesive mass, sealing a wound, promoting coagulant activity, sorbing a body fluid, and adhering to tissue. For example, the desired result can be sealing the wound using an adhesive cast made of clay minerals mixed with blood or other wound fluids.