Keeping moisture out of your home is a battle on many fronts. While the most obvious reasons for water damage are leaks in your roof or leaking pipes, a lot of water can make it into your house in a less obvious way. That is why vapor barriers are important. A vapor barrier consists of a thin sheet of polyethylene plastic, paint, or in some cases, even paper sheets. It keeps moisture from getting into your home, but only if it is installed correctly. If you use the paint, you need to make sure it covers the surface completely, and any scratches that you happen to make in the paint will need to be re-covered.
The plastic sheets, on the other hand, can be nailed in place, but when installing them, caution needs to be exercised, since they can rip easily, especially the thinner variants. There are sturdier variants that are made specifically for installation on a rough surface.