The bricks on my front porch have some sort of mortar that crumbles away more and more every time I pull a weed from it. You could pick this stuff away with an awl but it is not just sand that you might put between yard pavers. The depth from the top of the bricks to this "mortar" is about half an inch and growing. I believe this patio is about 12 years old. My questions are:
- What is this stuff?
- Can I add more over the top of existing?
- How can I stop it from crumbling?