I have a small about concrete building, housing a hydro turbine, it is all mass concrete including the roof, but there are one or two small damp patches where the roof meets the wall and I would like to stop this asap. Does anybody have a similar problem and what are the well proven remedies, I have used a water sealant for different areas around the farm, but on looking up professor google the lifespan of the stuff I have used previously has been pathetic, trouble is it doesn't show it's shortcomings until it's too late. I want something that will last for years.