Do you have to rough up the old flooring ?
Maybe. If the old vinyl tile is flat, then yes. If it is dimensional (has any type of raised surface), then you would have to use a flooring patching compound to level it (a lot of work). Also, you have to make sure the old vinyl tile is clean. Glue will not stick to a dirty surface. I would think it would be easier to get thin plywood, nail it down and put the vinyl tile on that.......
I tile, every day of my life, and while I'm not at all a fan of vinyl tile, you didn't state PEEL and STICK. Obviously the adhesives on Peel and Stick are inferior and as answer 1 suggests the tile can creep on any substrate. You also don't state any texture on the current tile, certainly to float anything over it is no less a task and challenge as it would be to remove the tile. For one thing a peel and stick needs almost a glass like finish for its inferior adhesive to be even modestly effective. That would relate to roughing up as well. Then there is the issue of how you might define Rough Up? I offer my opinion/ s First of all if it's peel and stick, I'd not bother, but if I bothered, my usual; course of action is a water based contact cement on both the substrate and the bottom side of the tile. That method can be used on non adhesive backed tile as well, but there are many viable/valid tile mastics on the market. A final note, no matter what tile or method you choose. DO NOT use the existing tiles as a guide to install new. If you choose to floor over though I cannot imagine doing so, you will be better served to displace seaming the new tile, (offset) at the seams, from the existing. Steven Wolf Just my two sense
You certainly do need to rough it up, you may also need to seal or prime it - I have seen new tiling 'creeping' over old, when the glue hasn't really been suitable. The best thing is to get recommendations from the tile manufacturer for the right adhesive for this situation (probably a solvent based one).
