I have never ruined an ironing board cover using starch; been starching fabrics since the 60's....is on in board covers are washable, starch washes away. Into don't use so much starch that it saturates,soaks the board. When I notice anything on my cover I take it off & launder it. If it am using a lot of fusible stabilizer products and not using my applique pressing sheet I use a sheet of freezer paper pressed to my ironing board cover; sometimes that stays on for a long and, when it becomes dirty or has build up on it I can peel it off & toss it.