My chimney leaks badly during a heavy rain; I have been unable to find a person who can tell me how to solve the problem. As I have unvented gas logs, I had the top of the chimney sealed.so it is not leaking from the top. Since I have been unable to find the leak, is there a product on the market that can be painted or sprayed on the outside of the chimney to prevent leaking? If not, do you have other suggestions? I have also thought of covering the chimney with some kind of cement or covering the present chimney with a prefab chimney. Please help! Thanks.