Abstract: A device for storing and mixing a plurality of paste components which, when mixed, form a hardenable composition, includes a base plate and a cover. The base plate has an upper planar surface bearing two or more non-self-leveling pastes and adhered thereon in spaced apart areas and. The cover is adhered to the upper surface of the base plate around the pastes and defines a chamber for the pastes. No portion of the cover contacts the pastes. The cover is removably affixed to the base plate, to allow exposure of the pastes for mixing together on the upper surface of the base plate.