A Tar Roof is an out dated system and therefore it is not installed onto many buildings anymore. If your old roof is made of tar and gravel, it is a matter of time before they will need to be replaced. Hydro Stop is a great material to install onto your roof system after you have removed the old tar. Should you wait for the old roof to leak? I would say absolutely not. It is not in your best interest to wait and see. Many business owners have been removing them asap. Please feel free to visit our site for further advice.