It is not a great idea to do plastering after roof slab concreting and proper cutting as plastering and concrete do not create a ‘harmonious’ bond. This may lead to cracks on the roof and then leakage too.
Kerala has become a leading market for roofing sheet material in the last decade and a half. Millions of houses, buildings, education institutions and towers have secured ‘shelter’ under the roofing sheet. However, it cannot be assumed that the roofing works of all these buildings are not proper. People do not know whether to blame the engineers or contractors or the materials and methods of concreting for the leakage.
It is a known fact that concrete does not absorb water much. Thousands of buildings that do not leak even without having waterproofing applications are the best example of this. A few coats of white cement application over the roof slab prevent heat inside the house. However, no one knows why it can’t prevent leakage.
Nb: All the dams in the world leak as all the sides of the dam are not equally sturdy to contain the immense pressure of water. Anticipating such leakages, the water is often allowed to flow downstream to lessen the impact. This is one of the most advanced design techniques for dams.