The Chimney Crown: The Most Overlooked Part of an Arlington, TX Chimney
The crown is the slab at the top of the chimney that almost nobody thinks about, and in the North Texas sun and storms it is the first thing to fail. Here is why it matters so much and how to tell when yours has gone.
What the crown is and the job it does
Ask most homeowners what the crown of a chimney is and you will get a blank look, which is fitting, because the crown is the part of the chimney nobody thinks about right up until it causes a problem. The crown is the slab of concrete or mortar that caps the top of the masonry, sloping away from the flue opening to shed water off the top of the chimney. It is, in effect, the chimney's roof. When it is sound, it sends rain and storm runoff sliding off the top and down the outside of the stack rather than into it, protecting the masonry, the liner, and everything below from the water that would otherwise pour straight in at the most vulnerable point.
Because the crown sits at the very top of the chimney, out of sight from the ground and forgotten in the living room below, it gets none of the attention it deserves for how important it is. Yet it is the single component that stands between the weather and the inside of the chimney at the most exposed point on the whole structure. A failed crown does not just stop protecting the chimney, it actively channels water into it, which is why a cracked crown is so often the root cause behind a whole list of more visible and more expensive problems further down. Understanding the crown is the key to understanding why so much chimney trouble starts at the top.
Why the North Texas climate is hard on a crown
The crown takes the worst of everything the North Texas sky delivers, and our particular climate is unusually hard on it. Through the long, blazing summers the sun bakes the crown day after day, and that relentless heat, along with the thermal expansion and contraction of heating up each day and cooling each night, works on the concrete or mortar until it develops surface cracks. Many crowns were also poorly built to begin with, a thin layer of ordinary mortar rather than a properly formed and sloped concrete slab with an overhang, and a poorly built crown cracks all the faster under that kind of sun. Once the cracks start, they only widen.
Then the storm season piles on. The hail this region is known for strikes the crown directly, chipping its surface and worsening the cracks the sun has already started, and the wind-driven rain of a North Texas storm drives water into every crack and opening. And while the soil movement that comes with our expansive clay works mainly on the lower structure, the stresses it puts through the whole stack reach the crown too. The combination is brutal, sun-cracking, hail damage, storm water, and structural stress all working on the one component at the top that is supposed to keep water out. It is no surprise that the crown is so often the first part of an Arlington chimney to fail.
- Long summers of intense sun that bake and crack the crown
- Daily thermal expansion and contraction widening the cracks
- Hail that chips the surface and worsens existing cracks
- Wind-driven storm rain forced into every opening
- Thin, poorly built crowns that crack far sooner than proper ones
What a failed crown lets happen below it
The reason a cracked crown matters so much is that it does not fail quietly and harmlessly, it turns from the chimney's protector into the chimney's biggest water source. Once cracks open up, the rain and storm runoff that the crown used to shed instead runs through those cracks straight into the top of the masonry. From there the water spreads downward and outward, and the damage follows. The top courses of brick soak up the water and, in the occasional hard freeze, spall and flake. The mortar joints absorb it and recede. The water reaches the flue, where on a clay liner it speeds the cracking of the tiles, and it reaches the smoke chamber and the damper, rusting the metal and breaking down the masonry.
Eventually that water works its way far enough to show up where the homeowner can finally see it, as staining or dampness on the wall or ceiling near the chimney breast, a damper that no longer closes cleanly, or a musty smell from the firebox. By the time those interior signs appear, the water has usually been coming in through the cracked crown for a good while, and the repair has grown from a simple crown reseal or rebuild into a list that may include masonry, a damper, and a reline. This cascade, from a small crack at the top to a major repair throughout, is the single best argument for paying attention to the one part of the chimney almost nobody thinks about.
Spotting crown trouble and getting it fixed in time
Because the crown is out of sight at the top of the chimney, its early failure is hard to catch from the living room, but a homeowner with a careful eye can spot the warning signs from the ground or from a safe vantage. Look at the top of the chimney, with binoculars if you have them, for visible cracks across the crown or a surface that has started to crumble. Watch for pieces of concrete or mortar showing up on the roof or in the yard below the chimney. And inside, treat staining near the chimney breast, a rusting damper, or a musty firebox smell as possible signs that water has been getting in at the top. None of this replaces a real look by someone who reads these chimneys for a living, but it tells you when it is time to call.
The good news about the crown is that, caught early, it is one of the more straightforward parts of the chimney to put right. A crown with minor cracks can often be sealed before water gets deep, and a crown that has cracked further can be rebuilt properly, formed and sloped with an overhang so it sheds water the way it should for years. Done in time, before the water has had seasons to work its way down, a crown repair stops the whole cascade before it reaches the expensive parts of the chimney below. That is the real lesson of the crown, the most overlooked part of the chimney is also one of the cheapest to fix when it is caught early and one of the most expensive to ignore.
The crown is the chimney's roof, and in the North Texas sun and hail it is usually the first thing to go, taking the rest of the chimney with it if it is ignored. We will look at your crown, photograph its condition, and tell you honestly whether it needs sealing, a rebuild, or nothing yet. Call 325-222-0849.
For an honest read on your Arlington chimney, call 325-222-0849.