Hot take: a 20 minute demo at the Nashville bindery meetup fixed my sagging text blocks
I went to the small bindery meetup in Nashville back in March, mostly to swap scrap paper and complain about glue. A woman named Dana was showing her coptic stitch journals and I noticed her text blocks sat dead flat with no gap at the spine. She said the trick was rounding and backing the block just a hair more than I was, then lining the spine with a strip of airplane linen instead of the kraft paper I had been using. I tried it on two practice blocks that night and both opened flat at the first page, which never happens with my usual method. Last week I rebound a 400 page novel for a customer and she sent a photo of it lying open on her kitchen table with zero spine sag. If anyone else backs their blocks with linen, what weight are you using?