Water seems to be everywhere this time of year. There is the soggy ground from the snow melting, April showers pushing those May flowers, swollen rivers, and the general dampness that permeates this season. Being the weird chimney guy that I am, I usually relate things back to what I think about for 10 hours a day – chimney’s hate water. I am talking about masonry chimneys of course. There are 5 main ways that water hurts chimneys:
1. They are hard to flash around when roofing. Because chimneys are plumb to the world, and most roofs are not, water runs down the roof and into the side of the chimney. If you flashing is intact, it will simply run around the chimney and off the roof. If your flashing is compromised, it is anybody’s guess where the water will end up. Flashing should be inspected every year for damaged or dried up caulk. A chimney cricket (the cutest name in construction!) can be built to divert water around the chimney. This is the best type of remedy. You have to think like water.
2. Rain, freeze, thaw, repeat. You will see brick faces start to pop off and you will find them in your yard. Masonry products are very porous and they absorb water easily. If your brick faces are saturated and then it freezes, your chimney will soon look like the surface of M-222. Chim-Saver water proofing is the best fix for this problem. It is an ionizing water repellent that is warranted for 10 years. It is different than a sealant (ie Thompson’s) in that it breathes and lets moisture out, but repels it from going in. It is very cool stuff.
3. Inside-out. Rain falling into a chimney will eat away mortar from the inside out. The rain water mixes with the sulfur in the creosote and makes sulfuric acid. By the time it is noticed on the exterior of the chimney, the mortar is gone. Your chimney is a big pile of bricks with nothing holding it together. Every chimney should have a chimney cap – period.
4. Inside-out part 2. Many chimneys are built with multiple flues. One or two for fireplaces, one or two for furnaces, hot water heaters, etc. When a natural gas or propane appliance is vented into a masonry chimney, it is only a matter of years before the chimney will be destroyed. It is much like the rain problem described above because one of the bi-products of burning gas is water. When your furnace is running, the inside of your chimney will be dripping wet from condensation. An aluminum liner is a must for a gas appliance vented into a brick chimney.
5. Unseasoned wood. Wood should be dried to 15-20% moisture content. When the MC is higher, you lose a lot of energy turning water to steam, and then the steam turns back to water inside your chimney and brings a lot of smoke particles with it. The result is that gooey black creosote that you will see dripping at the top of your chimney. If you see this, your wood is too wet. By the way, this is the stuff of chimney fires. It burns hot and long, usually damaging your chimney and burning a wall or two in the process.
You have to be diligent to keep water out of your chimney, but most fixes are long-term and do not require a lot of maintenance. Otherwise – ashes to ashes and dust to dust.
Matt Waite - Chimney Guy Owner Black Duck Chimney MI Mechanical Contractor - Specialty Wood & Gas