We have a large outdoor courtyard in South Texas - so it gets a lot of sun & is very hot during the day.

The porcelain tile has been installed over a concrete patio. There is a joint where two different concrete pours meet -- there is no reed bar securing the two sections of concrete. It appears that moisture is seeping through this joint/seam, so the tile is not securing properly.

We are repairing this section of tile, and are having difficulty locating a product that will seal the concrete and give us a secure base to install the new tile. I thought we might be able to find a type of 'rubber membrane' that will move as the seam moves from the heat and is resistant to moisture

Does anyone have any suggestions thanks!