Only use the sandpaper on flocked surfaces until the "felt" is removed to achieve a smooth surface. Do not use sandpaper on other types of surfaces.
On a smooth surface, you can use the patch on its own
On a more "complex" area (weld, corner, seam), a trekking mat or a self-inflating one, use the glue and the patch
Let the glue dry for 4 hours before applying the patch. Once the patch has been applied, you can reinflate the mattress immediately