A flashing for concrete board siding includes a substantially rigid panel, a guide protrusion, an interior protrusion and at least one strip of adhesive double-sided tape. The guide protrusion and interior protrusion are integrally formed with the panel at opposing ends. The at least one strip of adhesive double-sided tape is on an exterior face of the panel. In an embodiment, a channel separates two or more strips. Some embodiments include at least one groove disposed between two or more strips. Further, a method of installing concrete board siding to a structure includes fastening a first piece of cement board siding to the structure, providing an embodiment of the flashing disclosed herein, positioning the interior protrusion on the top edge, adhering a second piece of cement board siding to the least one strip of adhesive double-sided tape and fastening the second piece of cement board siding to the structure.