The spine area of the new spine cloth should be reinforced with an acid-free paper, or several layers of acid-free bond paper.
The spine inlay should be the same width as the text block spine and the height of the book boards, not the text block. It is a common mistake to cut the spine inlay the same height as the text block, which is shorter than the book boards.
Cut a spine inlay the width of the text block spine (original measurement A)
and longer than the height of the book boards. It will be trimmed later. The
grain of the spine liner must be parallel to the spine of the text block.
Double check the width of the spine inlay paper by laying it against the text block spine. It should fit the spine from shoulder to shoulder without curving into the joint area.
Trim the spine inlay to the correct height. Remember it should be the height of the cover boards, not the text block.