I'm about to take on my first floor tiling job. I'm using Hardibacker board. Most areas are a plywood subfloor. A few places are vinyl flooring. My thin-set mortar says unacceptable surfaces for adhesion include vinyl floors. Since I'm going to nail down the hardibacker anyways, can I still use the mortar over those areas for adhesion, or do I need to get a different adhesive for those small areas that are vinyl? House was built in 1985 so I understand I'm not to remove the flooring.