Does glue down flooring adhesive need to be removed before laying porcelain or ceramic tile?

From my experience, It is recommended to remove as much existing glue as possible then apply a sealer just for this purpose available at your local hardware store or tile shop. This creates a positive bond and will ensure a long lasting tile installation.

Take note that if your glue down flooring is glued down well and is not loose or coming up they make a couple of products that prep this flooring which allows tile installation to be applied right on top. I have not personally used this as I am an old school type of installer however I hear that these products work well.

StraferX