Chimney leaks frequently come from three common areas on fireplace chimneys. Chimney crown leaks, chimney flashing leaks, and brick chimney leaks. Different factors affect a chimney’s ability to resist water penetration such as the age of the chimney, the type of construction materials and its construction. In this article I’m going to reveal some specific problem areas and how you can solve your own chimney leaks.
Chimney Crown Leaks
First off, the chimney cap or masonry chimney crown. Over time, chimney crowns can crack or break off, allowing water to soak in and come inside the chase. This water can run down the chimney and absorb into the inside of your house. Additionally, crowns need to be made of concrete. However they are frequently made from mortar instead to save time and money.
The problem is that mortar is not as dense or as strong as concrete and is more likely to absorb water. If the crown is in too bad of shape, you may need to replace the crown. That can usually run anywhere between $500-$2,000.
If there are some severe cracks, but no missing pieces off the crown, my chimney sweep crews usually use a product called CrownSeal. It’s a flexible elastomeric product that you can trowel on over the surface of the crown. It fills in the gaps and seals the crown, preventing chimney water leaks. CrownCoat works even better for crowns with smaller cracks and in slightly better condition. It’s easier to apply and it dries faster. Read more about chimney crown repair in our article “Chimney Crown Repair” or our video “Chimney Crown Repair”.
Chimney Flashing Leaks
Chimney flashings are another potential source of water leaks. Where the chimney meets the roof line is a particular weak spot for water penetration because as rain water runs down the roof, it gathers and runs off right onto that joint.
Over time, as the chimney flashing deteriorates, water can gradually begin to seep into that joint and into your house, ruining drywall, causing wood rot and mold growth.
There’s a product called FlashSeal that you can apply on top of the chimney flashing to seal up this joint. There’s a mesh fabric to also apply underneath. This makes it even stronger.
Brick Chimney Leaks
The last problem area is the bricks and mortar joints. There are many different types of brick out there. The softer and more porous the brick, the more likely it’s going to leak. Mortar joints are another problem area. Many times, the mortar mix is has too much sand in it, causing it to soak up water like a sponge.
Also, many times the mortar joints are struck (packed in with a special tool) too shallow, causing water to be able to quickly absorb and pass through the thin layer of mortar. To prevent water penetration in brick and mortar joints, try a waterproofing product called ChimneySaver. It’s a breathable water repellent that you spray on your chimney with a pump-up sprayer. It actually forms a chemical bond with your masonry about 1/4″ below the surface, making the masonry repel water for 5-10 years.
If you have cracks in your mortar joints that are wide enough to stick a credit card in, you can use a product called CrackMagik. It fills in the cracks that are too large for the water repellent to fill. Most water repellents can fill hairline cracks. Any bigger cracks need to be filled either with a mortar crack chimney repair product such as CrackMagik, or for more severe cracks you will need to tuck point the mortar cracks with new mortar.
By protecting the chimney crown, flashing and brick and mortar, you’ll save yourself the expense of chimney water damage and eventual chimney replacement. Water damage causes over $1 Billion in damages every year. In most cases you can avoid this damage a little preventative maintenance once every 5-10 years.