Here is a diagram of what I am trying to achieve My patio is pretty much flat. Due to settling the water collects near the wall Since it is too much work to grade properly the entire patio I think that it would be good to rest the areas where the water collects and to add a french drain between the patio and the wall. The wall is presenting efflorescence due to too much water at the base. The water goes up on the wall due to capillarity pressure.
So ..what sort of can be used between the french drain and the patio (see the picture, the edge pointed by the arrow)
Someone on another site suggested something like this