Water Leaks in Masonry Chimneys

  Water  leaks in masonry chimneys. 

  There are many places a masonry chimney can leak. I have the best results addressing the chimney as a whole, (unless there is something obvious  like a flashing  that  has pulled away from the chimney.)

  I don’t like to attempt to solve leaks on chimneys with no rain cover. It doesn’t make sense to look for avenues for water penetration when there is a very large, uncovered hole at the top of the chimney.

  The flashing is a common point of entry for water. It should be secured to the sides of the chimney facing the roof and sealed 100% watertight with a high grade of caulking or sealant. Roof cement, silicone and vulcum are often used for this purpose.

If the roof slopes toward the chimney and the pitch of the roof  is steep or the chimney is wide,  the roof should have a hump or “cricket” built against the chimney to divert water away from it.

The cement crown should be free of cracks and should slope away from the chimney. Though flashings can be installed under a concrete crown, the most cost effective and waterproof products are flexible crown resurfacing agents. Properly applied, they create a 100% effective water barrier.

The sides of a masonry chimneyare usually brick, stone stucco or cinder block. They should be checked for cracked or deteriorating cement joints and defects within the brick, block, stone or stucco. These defects must be rectified professionally and completely.

The porosity of each type of brick, each type of stone and each type of cement varies, however. all of these materials  can be a source of water penetration. I suggest applying a very large amount of siloxane water repellent to virtually all leaky chimneys, (after a few days of dry weather is best.) Lots of water can soak through a masonry chimney and lots of water leaks are eliminated by applying water repellent. Siloxane is the best, because it lasts up to 10 years and penetrates the deepest, yet allows for chimneys to dry out because water vapors can pass through, while liquids, like rain water, cannot.

We frequently get calls to fix leaky chimneys that have been repaired unsuccessfully in the past.  A keen eye, careful, meticulous repairs )caulking, tuckpointing, etc.)  a very heavy application of water repellent, crown resurfacing and a rain cap, solve the vast majority of even the most persistent water leaks.

It is the workmen’s attention to detail and the thoroughness of  this approach that will make the difference.

Dave Myers,  CEO 301chimney (and 36 years of repairing chimney water leaks)