I would probably go ahead and wash the back, but not the top. When you've got it quilted and wash it, it may have a little shrinkage, but that kindof gives it a vintage look. I always wash my fatbacks, but I don't usually prewash my fabrics, and have not had any problems (knock on wood!) so far. I'd be afraid the top would ravel too much and maybe even come unsewed. Good luck whatever you decide.