Could you use a cotton batiste fabric for a foundation? I've been saving strings for quite some time. I have a bunch of batiste (or "lawn") that has seemed too thin to use as a backing. I have a couple of old telephone books, too. However, the thought of ripping all that paper off sounds daunting.
Here's a picture of a string quilt I want to make. It's on her home page
bkay
great string quilt