Well, I applied this specific material on the ceiling of a detached house on an island that had never been painted before, after sanding it with sandpaper because it had some "green spots". Since the terrace had scratches and small puddles, I first applied a diluted coat and the next day I went up to brush the puddles where the roller couldn't reach. I noticed that due to the temperature (heart of summer, after all), the material was still sticky and small flakes would come off when I left something on the terrace. The photo was taken after only one coat had been applied, and I decided to apply the second coat after 3-4 days to be sure. After one coat on a 40 sq.m area and the next day, considering the shortcomings I mentioned earlier, I still had 1/4 of the barrel left, so I will definitely need a second one, which I believe will be enough to apply even a (semi-finished) third coat! I cannot comment on water permeability because that will be evident over time, but it seems like there is a slight drop in temperature inside the house! And I was surprised that in a second small barrel that I used with the material and a little water I had added, if I didn't lower it every three minutes due to the heat, it would form a skin on top. Overall, I think it dries quickly when it's bare! I am currently satisfied!