I'm preparing to lay tile in a small basement bathroom over concrete, which previously had vinyl tile with black mastic adhesive. The previous tile had been down for quite a while so the mastic may contain asbestos and I don't want remove it by sanding or anything too aggressive. I've scraped off the high points, so it is a smooth surface, but it is still black in color. What is the best way to prepare this so the thinset will adhere properly? For several reasons, putting down cement board isn’t an option.
You could have a look at Sika rapid dpm, it can be used as a primer to isolate old adhesive residue, but i'd check with sika first, just to make sure it's suitable
