Why You Need to Install a Concrete Chimney Cap
If you've been looking up at your roof lately and wondering about that slab upon top of the particular flue, you're likely looking at a concrete chimney cap . Most people don't think twice about this until they discover water dripping in to their fireplace or notice cracks in their brickwork, yet that slab associated with concrete is in fact the first line of defense for your entire chimney system. It's basically the coverage for your house's venting system, plus if it's not really doing its work, you're going to have some pretty expensive headaches down the particular road.
I've seen plenty of homeowners mistake a "mortar wash" for a real cap, and that's usually where the problems starts. An actual concrete chimney cap —often called a chimney crown—is a dense, reinforced part of masonry that sits on top of the particular chimney structure. It's meant to take the brunt from the rainfall, snow, and sunlight so your stones don't have in order to.
Why concrete beats the alternatives
You may wonder why we all use concrete instead of just slathering some leftover mortar through the bricklaying procedure on top. Well, mortar is great for holding stones together, but it's actually pretty poor when it comes to standing up to the elements on its own. It shrinks as it cures, that leads to tiny hairline cracks almost immediately. Those cracks allow in water, the water freezes, and abruptly your "cap" will be falling apart in chunks.
A poured concrete chimney cap , on the other hand, is a different beast entirely. It's made with a mix that contains larger aggregate, making it much more durable and resistant to the continuous expansion and contraction that happens with the particular weather. When it's done right, this can last decades, whereas a basic mortar wash may start failing within just a couple of years.
The importance of the "overhang"
One of the biggest mistakes I see in chimney construction is a cap that sits flush with the stones. If your concrete chimney cap doesn't hang more than the edges of the chimney, it's not doing the job properly. You want that concrete in order to stick out from least two or three ins past the brickwork on all edges.
Why? Because of something called a drip edge. When rain hits the very best of your chimney, you need it to eliminate the part and fall directly down to the roof. If the cap is flush, the water simply rolls right straight down the face of your bricks. With time, that water soaks directly into the mortar joint parts between the bricks, resulting in "spalling"—that's when the faces of the bricks start popping off. This looks terrible, plus it's a complete pain to fix. A good overhang with a small groove (the drip edge) cut directly into the bottom will keep your chimney dried out and your brickwork happy.
Building one the right way
In case you're thinking about the DIY project or even hiring someone to pour a new one particular, there are the few things that shouldn't be missed. First of all, a concrete chimney cap must be thick—usually with least three or four inches at the thickest point. It need to become sloped. A person don't want standing water sitting upon top of your own chimney; you want it to run away as quickly since possible.
Encouragement is another large one. Throwing several wire mesh or even a bit of rebar in to the concrete while it's being poured gives it the particular internal strength it needs to remain in one item. Since the chimney is constantly heating up and cooling down when you use the fireplace, that concrete is usually going to proceed. The reinforcement assists it stay jointly even if it evolves a little surface crack.
Bond pauses and expansion joints
Here's the technical bit that's actually super important: the cap shouldn't be stuck straight to the clay-based flue liner. When you pour the particular concrete right upward contrary to the flue, when that flue gets hot from a fire, it's going to expand. In the event that it's stuck towards the concrete, it'll break the cap right open.
Pros use what they call a "bond break. " They will wrap the flue in something such as foam or a thick layer associated with expansion joint materials before pouring the particular concrete chimney cap . This gives the flue room to breathe without wrecking the masonry. After that, you just fill up that tiny gap at the top with the high-quality flexible sealant to keep the water out.
Coping with cracks and maintenance
Even the particular best-built concrete chimney cap isn't completely "set it and forget this. " You ought to probably pick it up once a year—or have a sweep look in it—to check intended for cracks. Tiny breaks are normal, yet they need in order to be sealed prior to they become huge ones.
In case you catch all of them early, you can usually just brush on a breathable masonry sealant. These products are pretty awesome because they're "hydrophobic"—they literally push water away—but they nevertheless let moisture stuck inside the concrete escape. If you use a non-breathable sealer, you may in fact trap water inside, which causes more damage when it freezes.
If the cracks are usually wider than the dime, you're searching at a more serious repair. From that point, you might need to use a specialized masonry caulk or, in some instances, look into having a new cap poured on the old one particular.
The price of ignoring it
I understand, it's hard to get excited about spending money on some thing you can barely see from the driveway. But a failed concrete chimney cap is an absolute chimney-killer. I've seen chimneys where the water got in through the particular top and rotted out the firebox, rusted the impediment shut, and actually caused mold in the walls encircling the fireplace.
Fixing all those issues could cost thousands of dollars. Compare and contrast that to the cost of flowing a solid concrete chimney cap or simply keeping a good existing one covered, and the choice is pretty obvious. It's one of all those "ounce of prevention" situations that actually will pay off in the particular long run.
Choosing the correct finish
Whilst functionality may be the main goal, you can actually make a concrete chimney cap look pretty decent. Some people like the raw, industrial look of grey concrete, but you may also add pigments to the blend if you want it in order to match the color of your house or even the brickwork.
In addition there are ornamental pre-cast options. These types of are made within a store and then hoisted up to the roof. They're often really high quality mainly because the concrete is cured inside a handled environment, but man, they are heavy . If you're heading that route, make sure that your chimney structure is usually solid enough to handle the weight.
Is it a DIY project?
To be honest, it depends on how comfortable you might be on a ladder and exactly how very much you like heavy lifting. Mixing concrete on the terrain and then hauling buckets of this up a ladder is really a workout a person might not want. Plus, building the wooden "forms" that will hold the moist concrete in place while it sets can be the bit tricky when you're working in a height.
If you've obtained a low-slope roof and some fundamental carpentry skills, a person can definitely manage a concrete chimney cap project. Just don't sacrifice quality on the components. Use a high strength concrete mix, don't your investment rebar, and make sure you have a plan for how to get the moist concrete up presently there without making the huge mess of your shingles.
Wrapping it just about all up
From the end of the day, your own chimney is the giant hole within your roof, plus the concrete chimney cap will be the only thing keeping the outdoors through coming inside. Whether you're building the new home or even just trying to keep your current a single in good shape, paying interest to the condition of this concrete slab is a smart move. It's not the most glamorous part of homeownership, but keeping the particular water out is the greatest thing you can do for your chimney's lifespan. Take a peek up there this weekend—your fireplace will thank you with regard to it.