Yes, it is highly recommended to wash a floor after sanding. Sanding floors often leave behind dust and debris, which can be difficult to remove without proper cleaning. Washing the floor removes this buildup and can help to prevent damage to the floor's finish. Additionally, washing a floor after sanding will help to ensure the best possible results for your refinishing project. It is important to follow the manufacturer's instructions for your specific floor and cleaning product in order to achieve desired results.