when the floor slab was cast some of the polythene membrane disappeared into the concrete. when we had a lot of rain last week we had a puddle on the floor by the low level window. The builder has coated the inside of the floor and the thermalite blocks that weren't covered by the membrane with bitumen. Is this OK? My thought was that the bitumen will eventually dry and crack or that there might be some settlement and get cracks which will let more water in. Am I wrong?