preparing to tile floor
upon removing the old tile I found a blackish substance that didnt adhear to the old tile and was told that it was probably an oil base coating that was applied for a vynal floor that must have been there in the past. How do I get that off the floor to get ready to install travertine floor tile with thinset so it will adhear to the concret floor. It was suggested to sand the floor to open up the pours of the concrete floor so the thin set will stick. Is that my best option?