There can be several problems with the weathering course laid on top in the terrace. I am facing a very peculiar problem with it. In my apartment, we are seeing water dripping out the roof via the parapet-roof joints several days after rain. Water oozes out via a crack that has formed at the joint of the parapet wall and the roof RCC. Also, the dripping is happening near the roof drain vents, which happens to the lowest area of the roof-top.
Generally while constructing roof and weathering course, masons leave an inclination of level towards a corner of the roof for the rain water to drain comfortably. In our case, we are seeing water draining through a crack between the parapet wall and the roof in the vicinity of the drain vent. Since it is near the drain vent, we were suspecting the thickness of the weathering course. As there is a forced inclination in the weathering course layer, the thickness of the course near the vent should be lesser than the other areas of the roof.
When we consulted with a civil engineer, he was giving a completely different explanation for the problem. He was suspecting the iron-oxide coated shells layered on top the weathering course. He was saying rain water might have gotten into the core of the weathering course through the gaps between the iron-oxide shells. The water thus gotten inside keeps the weathering course in soaked condition for a long time. Here the core of the weathering course behaves like a sponge to absorb all the water that seeps inside. Later, the water thus absorbed percolate to the lowest side of the roof slowly, which may take weeks time (like our case). Once the amount of water reach a significant quantity at the lowest side, it tries to escape somehow. In our case, the escape vent is a crack that had formed between the roof RCC and parapet wall construction.
So what is the solution to this problem? Should we take out the weathering course completely and redo from scratch? Should we be finding the source of the problem, the places were rain water seeps inside the core of the weathering course? Should we increase the thickness of the lowest side of the roof ? All these cannot be permanent solutions or they may not be easily doable. The
solution that I have is the following. Since the water collected is trying to escape, let’s give it an easy way to escape. Finally, we don’t want the core to be soaked. So we should be placing vent pipes just above the RCC roof level and be placed amidst the core of the weathering course at the lowest side of the roof. We know that water from all the areas are reaching here percolating for weeks. If there is an easy vent out like the vent pipe, the accumulated water can escape easily instead of dripping out of a crack. If we can find potential spots in the roof for more vent holes, we may very well preserve the consistency of the core of the weathering course for a long time. But that’s going to be pretty tricky!!