6. Is waterproof stucco superior to
weather- resistant stucco?
No, absolutely not! Why not? Because no building can be kept waterproofed. Water always finds its way past a face seal, especially where there are penetrations through the stucco, such as windows, doors, deck intersections, compression joints. Our instructor at the Building Envelope Professional course at Simon Fraser University put it this way.
30 miles an hour of wind driven rain puts a pressure on the wall equivalent to one inch of water in a swimming pool. If you have 60 miles an hour of wind driven rain then it is like 2 inches of water in a pool. "Now, how often do you get rain in Vancouver?" he asked He was from the United States but he knew that it rarely stopped raining in Vancouver. He said, "Ok….now let's take the wall that you are designing, or building, or repairing or analyzing and lay it flat on the ground. Let's pour 1 inch of water onto the wall until it covers every part of it…a full one to two inches deep." "Will water get inside???" he asked. Well obviously everyone answered, "Of course." "So stop building, repairing, and designing walls to keep water out…because you can’t! Start building, designing, and repairing walls to let water out because it is going to get in!"
So waterproof, face sealed stucco will let water passed its face and once it does remember….it is waterproof from both sides. That means that water that gets in will stay in, because the face is sealed with a waterproof coating. Oh yes they say it is breathable….and it does have a measureable breathability factor on some kind of a scientific standard (after all, you can suffocate a person with a "breathable" pillow!)….but it's not enough…it might discharge a bit of moisture vapor common to an occupied home…but it will never discharge liquid water. It will build up and it will rot your wood!