I just did two string blocks from taking the free classes at
www.craftsy.com. Go to online classes and look down to the left and click on quilting, the it's about the third or fourth row down. It's the free block of the month. It's on the right of the page. I think it's the first month, but I'm not sure. She has a video and walks you through the two different type of string blocks. One of them uses a backing to sew the pieces of fabric to and the other has you cut the muslin but you just use it as a guide. I think you want to do the second one. Not necessarily the pattern of that particular block, but the way she makes the block without using any backing at the end. Her classes are great! I've made 6 blocks, 2 a month, and it's free!! Check it out.