Gap Between Shoe Molding And Floor . There are instances when you need to fill the gap between floor and trim, but you don’t want to use shoe molding. Both shoe molding and quarter round cover the gap between the baseboard (a larger piece of trim) and the floor. insulation Easy way to temporarily insulate gap between hardwood from diy.stackexchange.com The gap between the old and new floorboards should be closed or low enough just to keep cold air out. Fill any holes with wood putty. Considering how important shoe molding is, what are the main types that you should be aware of?