Water Leaks around Brick Chimneys
      What are the Causes and Cures?

                by Joe Mehaffey

Many homeowners have problems with water leakage  associated with brick chimneys.  This can manifest in a number of ways such as:
1) Water runs down the flue.
2) Water runs down the brickwork inside the house or attic.
3) Exposed chimney brickwork gets damp and white lime deposits form on the surface of the brick.  In this case,  the water may/may not run out.  It can be that the brick just gets damp when it rains.

There can be a number of causes for this.

1) It may be that the flashing around the chimney is inadequate,  worn, corroded,  or that it was improperly installed in the first place.  This is USUALLY verifiable fy the simple test of running a low pressure hose around the chimney to roof intersection and see if any water comes inside.  If you see any water at all repairs are needed.

2) It may be that the top of the chimney is cracked or loose and that water is entering at the top and running down inside the chimney and coming out anywhere along the way.  How can this happen you ask?  Aren't chimneys SOLID brick.  The answer is yes and no.  Chimneys are usually solid brick but sometimes concrete blocks or other solid filler materials are used INSIDE the chimney and the outside is brick veneer.  Sometimes the inside of the chimney is built up of brick that are "just thrown in" and haphazardly filled in with mortar.  While this is usually structurally OK,  it can leave channels, cracks and crevices where water can migrate from the top of the chimney all the way down.  These crevices can, in the aggregate, hold many gallons of water and you may have a big rain one week and the chimney brick inside your house can stay damp for weeks.. There are a sevaral answers to this problem.  a) In a new chimney installation insist that the bricklayers use great care to COMPLETELY fill the interior with brick and mortar so that there are no cracks and crevices to begin with.  This will likely take the average crew an extra half day on a typical chimney.  b) Have the brick masons use hydraulic cement for mortar for the last 5 feet or so of the chimney near the top.  Hydraulic mortar is non porous and if placed solidly will not allow water penetration.  c) If the chimney is already built then a) and b) are not practical.  In such case,  have the entire top of the chimney covered with a lead coated copper sheet cover.  This will act as a roof on the chimney.  This will prevent water from entering the top of the chimney in the first place through cracks in the mortar and brickwork.  This is also a good time to put a bird screen and cap on the flue if you do not already have one..

3) Many "fashionable" brick used these days is rough and  porous on the surface.   If you find you have a leak around the flashing and the flashing is just glued flat to the brick (NEVER the proper way) instead of  the stepped flashing being slipped into a one inch slot (previously filled with silicone caulk), then you may as well get ready because this flashing WILL eventually leak.  The flashing should be either copper (good) or lead coated copper (better) or lead (best) if it is in contact with brick.  Aluminum flashing (frequently used) will usually corrode in as little as 5 years in contact with wet masonry.  Copper flashing will usually last 20+ years,  lead coated copper 75 years and lead 250 years.  All these times assume PROPER installation by a craftsman versed in his trade and not just the local handyman.  Some roofers may propose "sealing" your porous brick with some kind of paint product.  This cannot HURT,  but most paint products will fail quickly.  One product which I have used for about 5 years that seems to be holding up well is "Lifetime" Silicone waterproofing sealant.  I have used this product on concrete and on brick and it works very well and seems as good at five years as when new.  If it will go the claimed 20+ years, I cannot say.

If your leaking chimney is positioned so that a good bit of water impacts the "up the roof" side of the chimney,  you should have a "cricket" in back of the chimney.  The cricket is a small "roof" type structure that causes water flowing toward the chimney from upwards on the roof to divert to either side of the chimney and not impact right into the chimney and it's associated flashing.  Crickets can be added after the house is built if necessary,  but they are best and most cheaply installed at the time a house is constructed.

If you have lightning rods installed in your house while it is being built,  you can have the masons bury the wire to the lightning rod protecting the chimney INSIDE the chimney structure as they build it.