Most expensive chimney repairs start at the top, where water gets in. Caps and crowns are the cheapest protection your chimney has, and the parts most often neglected. Ace Chimney Service fits and repairs both across Crystal Lake and McHenry County.
Two different parts, two different jobs
They get spoken about together and confused constantly, so it is worth being precise.
The crown is the slab across the top of the masonry. It should be cast concrete, sloped so water runs off, and it should overhang the brickwork with a drip edge so runoff falls clear rather than tracking down the face. Its job is to shed water off the whole structure.
The cap sits over the flue opening. It keeps rain out of the flue itself, screens out animals, and arrests sparks. Its job is to protect the opening.
A chimney can have a perfect cap and still be soaking up water through a failed crown — which is why both get checked together.
How crowns fail
A great many crowns were never built properly to begin with. The common shortcut is a thin skim of mortar troweled flat across the top instead of a proper sloped concrete slab. Mortar is not designed for that exposure. It cracks within a few years, and once it does, water runs directly into the space between the flue liner and the masonry.
From there the damage is hidden and steady. Water in that void freezes, expands, and pushes the masonry apart from the inside. The first thing most homeowners notice is a damp patch on the chimney breast or white staining on the outside brick — by which point water has been getting in for a while. The masonry repairs that follow cost many times what recasting the crown would have.
What we install
- Stainless steel caps — single and multi-flue, with mesh sized to keep animals out without restricting draft
- Recast crowns — properly sloped, reinforced, with an overhang and drip edge
- Crown sealing — flexible waterproof coating where the slab is sound but showing hairline cracks
- Stainless chase covers — replacing rusted galvanised covers on factory-built chimneys
- Top-sealing dampers — closing the flue at the top, which seals far better than a worn throat damper
We fit stainless rather than galvanised as a matter of course. Galvanised steel is cheaper and rusts through, and on a component whose entire purpose is keeping water out, that is a false economy.
Why this is worth doing before winter
Water already inside the masonry when the first hard freeze arrives is what does the damage. Every freeze-thaw cycle drives the deterioration further, and northern Illinois delivers dozens of them between November and March. Getting the top of the stack sealed before that starts is the single most cost-effective thing you can do for a masonry chimney.
Cap and crown condition is assessed as part of every inspection, and we photograph what we find rather than simply describing it.
Call (815) 320-0883 or book online. We are open 7am to 7pm, seven days a week, and pricing is on our pricing page.
Frequently Asked Questions
What does a chimney cap actually do?
Three things: it keeps rain out of the flue, it stops birds and animals nesting inside, and its spark arrestor screen stops embers landing on the roof.
What is the difference between a cap and a crown?
The crown is the sloped concrete slab across the top of the masonry that sheds water off the structure. The cap is the metal cover over the flue opening itself. They are different parts and they fail differently.
How do I know if my crown is cracked?
From the ground you often cannot. Signs that show up indoors are damp patches on the chimney breast, white efflorescence staining on the exterior brick, and mortar deteriorating near the top of the stack.
Can a cracked crown be repaired or must it be replaced?
Fine hairline cracks can be sealed with a flexible crown coating. Once the cracks are wide, the slab is spalling, or sections have broken away, sealing it just hides the problem and it needs recasting.
Why do animals get into chimneys?
An uncapped flue is a warm, sheltered vertical shaft — ideal for chimney swifts, squirrels, and raccoons. A cap with proper mesh prevents it entirely, and costs far less than removing a nest and sweeping afterwards.
What is a chase cover?
On a factory-built chimney enclosed in a wood-framed chase, the chase cover is the metal lid over the top. Galvanised covers rust through and leak; stainless steel ones do not, which is why we fit stainless.
My cap is rusted. Does that matter?
Yes. A rusted cap sheds rust stains down the masonry and eventually fails altogether, letting water straight into the flue. Replacing it is one of the cheapest pieces of chimney protection there is.
Do gas fireplaces need a cap?
Yes. Gas appliances still need the flue kept clear of rain, debris, and nesting, and the exhaust is corrosive enough that water sitting in the flue causes real damage.
Published: July 24, 2026