Tiling over Tile?

Hello,

Remodeling our small master bath and really need to save time by tiling over tile.

What steps are critical?

The tile is in good shape, floor is level. Do I need to cover with a thinset membrane or just clean and perhaps rough sand it?

Your advice is sincerely appreciated!

Norm

Clean and rough sand it. When setting the tile, use an unmodified thinset mixed with a liquid latex additive to give it some extra strength.