 I'm not so sure if it's designed to work on walls, but I know it works on sidewalks. But they have another patching compound that's designed specifically for, like, cracked steps and stoops, and that certainly would work on a chimney. And they adhere very, very well, and that's the key. They bind with the masonry surface underneath, and that's what gives you the longevity. Because, of course, what happens is...