All About Chimney Water Damage (and How to Fix It)

Chimney Water DamageChimneys, especially big heavy-duty masonry types, are often seen as indestructible and without need for care or upkeep. While this is somewhat true, the experts here at Chimney Sweeps of America want you to know all the facts about chimney water damage. With this information, you can avoid issues, spare your wallet and simply enjoy a cozy night by a properly working fireplace.

Now, most chimneys are hardy and don’t require a lot of effort on your part to keep performing without any major issues. However, a chimney that’s improperly protected from the elements and doesn’t receive occasional maintenance can end up suffering expensive chimney water damage.

Plus, some issues such as flue obstructions, loose masonry materials, and lining systems damaged by the weather can pose a dangerous threat to your home and everyone who lives under your roof.

Masonry Chimneys

Let’s quickly clarify what we’re talking about when we say masonry chimneys just in case you’re unsure if you chimney falls into this category or not. Masonry chimneys consist of materials such as brick, stone, flue tile, mortar, concrete, concrete block, as well as a few metals such as cast iron and steel.

If you have a masonry chimney, it will have been built with some combination of these materials. As we mentioned, water under the right conditions is incredibly powerful and nearly all these materials will at some point or another succumb to its effects, often sustaining heavy and costly chimney water damage.

The Force of Water

How do you end up with thousands of dollars in chimney water damage? Let’s think back to high school science. Water in its liquid form takes up a certain amount of space. When water freezes, it takes up more space and therefore must expand. Water is strong, and this process is remarkably challenging to contain, so if water has managed to penetrate even the strongest of masonry materials, start watching for cracks to appear when the temperature drops.

If water has gotten inside your masonry materials and begins freezing, thawing, and refreezing again, this constant expansion and contraction will cause the chimney to quickly begin deteriorating. The only exception to this is stone. However, keep in mind that stone is held together with large amounts of mortar so even if you have a stone chimney and think you are safe, the mortar is susceptible to the force of water so you are not out of the woods at all and still should think about proper weather protection.

Water also causes problems for the metal parts of your masonry chimney. Both cast iron and steel can rust in the extended presence of water which will begin weakening and eventually destroy any metal parts of your chimney.

Still not convinced that water can be so harmful? Here’s a handy list of chimney water damage:

  • Cause the damper assembly to rust
  • Cause the metal or masonry firebox assembly to deteriorate
  • Leave water stains on the ceiling and walls
  • Clog up the cleanout area
  • Cause any adjacent wood to rot
  • Ruin wall coverings
  • Cause the exterior mortar to decay
  • Stain the exterior or the chimney
  • Cause the flue lining system to crack or deteriorate
  • Cause the chimney to settle
  • Cause the hearth support to collapse
  • Or cause the entire chimney structure to collapse

As you can see, water is a heavy-duty force, and the dangers should not be taken lightly. One additional, annoying fact is that if you have a wood burning chimney, water can mix with the creosote and create a nasty smell that can fill your home.

Now that we’ve got all the bad news out of the way, it’s time for some good news. Chimney water damage is preventable, and the steps you should take are not necessarily expensive, especially once you compare it to the cost of rebuilding or repairing your chimney.

Chimney Caps

A chimney cap, sometimes called a rain cover, is a very popular and relatively inexpensive method for preventing chimney water damage. As part of the basic design of a chimney, it has a large opening (the flue) at the top. Some chimneys have more than one of these. Rainwater can easily get into this opening and start wreaking havoc as soon as freezing temperatures arrive. A chimney cap is an effective method to prevent water from entering the flue.

It has some other great side benefits as well. Sometimes, small animals or birds will get inside during the summer. They can cause clogs and their own brand of damage, but a correctly designed chimney cap will keep them out also. Another important function is it prevents any live sparks from escaping your chimney and landing on your roof or any other nearby combustible materials.

There are a few requirements that chimney caps should meet to be effective and well-designed including a design to be easily removable so that it can be properly inspected and cleaned. Plus, for obvious reasons, it should be made of a corrosion resistant, durable, and sturdy material.


If your chimney is located on the downhill slope of your roof and water runoff is always being thrown against it, installing a cricket to divert water is a good way to prevent issues. This deflector will direct runoff away from the chimney and help prevent any leaks into your home. If your chimney is over 30 inches wide or you have a very steep roof, a cricket is highly recommended.

Products to Prevent Chimney Water Damage

Most masonry materials are very porous, which means they will quickly wick water and moisture into the interior of the chimney. To prevent this, there are several waterproofing products you can buy and apply to your chimney. Always use products specially designed for this and not paints or clear sealers. These products might block moisture, but they also prevent vapors from escaping. A product specifically designed for waterproofing a chimney will protect it without trapping vapors inside the chimney.

We hope that this information about chimney water damage has been helpful. Of course, if you need help protecting this valuable structure, the experts here at Chimney Sweeps of America are here to help. If it has been a while since the last time your chimney had a checkup, give us a call today and we will make sure everything is in proper and safe shape!

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