Used this product plus a 1 gallon chimney cap repair with a brush and 1 gallon masonry water deflector on a large 3 foot wide, 5 foot long and 4 foot tall chimney that was built and started in 1970. to chip the brickwork a bit, it has leaked in the past and was repaired many years ago. All products were easy to apply and more than adequately covered the entire chimney with two coats. Even in heavy rain I didn't notice any problems. Will be used as needed in the future, but expect a long service life. Hoping to use the extra flashing product left around some skylights. Just follow the instructions and you can't go wrong.