There are a lot of people out there that make the mistake of assuming that, as long as they waterproof the inside of their basement walls, their home will be protected. However, it is important to learn why you should hire a contractor for exterior waterproofing as well. Here are some of the reasons you will want to do this. You Stop The Water From Entering Your Foundation Wall Interior waterproofing, without the exterior treated as well, will still allow water to penetrate through the wall.