Your chimney proudly defends your home like a warrior as it battles the ravages of wind, fire and rain with a badge of courage. With its sheer strength and tenacity, a well-built brick masonry chimney can last nearly a century leaving many homeowners to wonder, “Why should I waterproof my chimney?”
The majority of masonry chimneys are built with bricks or stone bonded with mortar, a cement material, to form a sturdy and practically impenetrable structure. But like most structures, water is a mortal enemy that can bring down a chimney like a falling deck of cards. “All masonry chimney construction materials, except stone, will suffer accelerated deterioration as a result of prolonged contact with water,” according to the Chimney Safety Institute of America (CSIA).
This is because bricks are composed of clay which is a soft and porous material. During the brick-making process a waterproof hard outer shell is baked in to prevent the bricks from soaking up water. But its continued exposure to periods of heat and cold, wind, rain and snow can take a beating that can eventually begin to pierce the outer layer of the bricks. Without waterproofing the chimney tiny holes will begin to form in the brick surface like a sponge that will gradually grow larger allowing water to penetrate the flue and damage other chimney components.
In addition, excessive exposure to moisture will also soften the mortar. Left untreated it will eventually melt away where you may notice large gaps between the bricks or stone masonry that will also enable water to leak inside the chimney. In extreme cases where chimneys have not been maintained for years it is not unusual to spot missing bricks and mortar. The chimney may also begin to lean as the foundation shifts due to its weight. This can also damage the structure of the home as the chimney pulls apart from the flashing material attached to the roof.
As a result, chimney masonry should be protected from exposure to water. That’s why many chimney professionals recommend homeowners apply a waterproof sealer to protect the chimney from water damage. It’s important to bear in mind that the waterproof coating will wear over time and gradually lose its effectiveness. So for optimum performance, waterproofing should be re-applied every five years.
However, it is highly recommended homeowners have a chimney inspection before waterproofing a chimney to determine the extent of repairs, if necessary, to spalling or missing bricks. Chimney deterioration may require tuck pointing work to replace missing mortar and will need to be completed before waterproofing.
Also, homeowners can extend the life of masonry chimneys by avoiding high pressure power washing. The high water pressure can crack the brick’s hard surface and damage the effectiveness of waterproofing. The exterior of masonry chimneys should be cleaned using a low pressure hose and a mild detergent.