The tiles are becoming loose on the steps to my home and need to be replaced. As I pull some of them off I discovered this black sheet under the tiles. It smells tarry and has a texture between fabric and chewing gum. It's somewhat sticky and in places it's very stretchy. Some parts are really easy to pull off of the concrete base, and in other places it sticks incredibly well. This material seems to be only present in that right-hand low plateau, not anywhere else.
- What is this sheet made of?
- What is its purpose? Why is it here?
- Should I use a similar sheet again?
To add some details, the base is made of solid concrete and it was built only 5 years ago. The tiles are coming loose not because the mortar is poor but apparently because the concrete was surface treated somehow and that treatment is coming off.
I can very easily remove most of the vertical tiles with just two fingers, and the back side of the tile has its glue firmly attached and also a thin layer of this other, darker color which comes off completely from the concrete. You can see it best in the vertical part on the top left of the third picture above. The horizontal tiles are stuck much better but not everywhere.