Step 12: Glue the paper into the covers
Smear some white glue (or rubber solution glue) in two stripes down the middle edges of the cover boards being careful not to get any glue on the spine board.
Then place the bound paper wad so that it is centrally resting on the spine board and ONLY the thing cotton "wings" are glued to the cover boards.
The spine should NOT be glued to the bound paper wad, although you should make sure that it IS glued to the cover boards right up to their edges, because this is the join that makes the book strong and stops the page block falling out of the cover.
It is best if you wait for this part to dry before moving on to the next step. It is probably a good idea to leave the book lying on its back with the paper was supported by to food cans while it dries, because, if you leave it to dry closed, bits of it might stick together that you don't want sticking together.