I love precuts, but its impractical to prewash them. After you piece your quilt you could wash the top and backing in a product called Retayne. It sets the dyes so that there is no bleeding. I just finished a quilt made with a batik charm pack of all different colors and black kona cotton. Washed the top with Retayne prior to taking it to the LA. Not one run or streak from the batiks or the black! Woohoo!