I am remodeling a bathroom in a 100 year old house. The bathroom was remodeled approximately 50 years ago. Ceramic tile was laid over the original tile, a beautiful one inch octagon shaped tile. The second layer is coming up without damage to the original and I would like to restore the original. However, there are considerable amounts of of very hard mortar remaining. Is there any way to remove this mortar without damaging the original tile surface?