Revisions log for Answer #948

Fiber cement boards should not be glued.

The back side will pick up moisture from the wall and deteriorate over time. That's what a vented gap is for, to dry condensation from the wall.

In the picture you have a gap of about 2-3 cm. Make a frame out of wood and put Cedral there so that its top goes under the window sill of the glazing. Only the ventilation gap will not be 4 cm, but 2. For such an area it is quite acceptable. Or make a normal plane, and redo the upper sill. It's pretty simple).

Under the porch, on the other hand, you were a little hasty with the last tile.

Your best bet is to tile where there are steps with glue, or something else. And the porch, where the glazing – do fiber cement.