I make string blocks all the time. My suggestion would be a light sashing between the blocks. Another suggestion which I haven't tried yet would be to use a plain color to make HST out of the blocks and put them together. Making these blocks are so addicting and I always have a pile of them done. What do you use for your foundation? I started out using paper but did not like tearing all the paper off the back so started using muslin, as flimsy as I could find. Really like the result. Have fun.