New mull on top of old?

[VeritySteele]

Hello, I'm trying to repair a 1,200-page book (spine thickness, 4cms). The text block is in good condition, but the part of the mull (only 1cm wide) that was stuck to one of the boards had come adrift, which threatened to cause a split along the length of the end paper, separating it from the text block. In addition, the whole text block had erroneously been inserted into the board cover upside down, so I will be correcting that, too.
I've lifted the end papers from the boards (they won't be reusable, I'm afraid) and am wondering what to do now.
This is probably not good book-binding practice, but could I stick a new piece of mull, with perhaps a 2cm overhang on each side, on top of the old mull? I'm also thinking of inserting a 'hollow' to provide extra support. I'd then reattach the mull to the boards and apply new end papers.
I'm new to this craft, so would appreciate any advice.
Thank you.

 

[Mobile-Promise46]

You're on the right track! Adding a new mull with a wider overhang is a good fix, especially if the old one's too narrow. A hollow is a great idea for extra strength and flexibility. Just make sure it's well-sized to the spine. Once that's in place, reattaching to the boards and adding fresh end papers should give it a clean, sturdy finish.