Chimney and fireplace symptoms
The inside of my chimney looks black, shiny and tarry
Black, glassy creosote is third degree glaze, fuel for a chimney fire, and in Portland we usually trace it to smoldering fires in a cold flue. Keep the fireplace or stove cold until the glaze is removed and a camera checks the flue.
Updated
What to do right now
Do not light another fire in that fireplace or stove until the glaze has been removed and a camera has looked at the flue. Glaze is concentrated, flammable tar sitting in the flue. If the chimney ever roars or throws flame from the top, get everyone out of the house, then call 911.
Likely causes, most common first
Glaze is a record of how the fires were burned, and these are the habits and flue conditions that write it.
- Most common
Slow, smoldering fires with the air shut down
The sign: Overnight loads in a stove or insert, lazy dark smoke from the chimney top, and door glass that browns over within a day of cleaning.
The fix: Chemical treatment and rotary tools strip the glaze, and the visit ends with a plain talk about hotter, shorter burns. Creosote Removal, from $449
- Common
Firewood that was never dry
The sign: Logs that hiss and bubble at the ends, steamy white smoke, and a woodpile split this summer or left uncovered in the rain.
The fix: Switch to wood dried under a roof for at least six months, then keep the flue swept so new deposits stay at the flaky stage. Chimney Sweep, from $249
- Common
A cold exterior chimney or a flue far too big for the appliance
The sign: Glaze thickest near the top of the flue, a brick chimney on an outside wall, or a small stove venting into a fireplace-sized flue.
The fix: An insulated stainless liner matched to the appliance keeps flue gas warm enough to leave as smoke instead of condensing as tar. Chimney Liner Installation, from $1999
- Common
An insert pushed into the fireplace with no liner above it
The sign: Tar dripping from the connector joints, a pool of hardened creosote on the smoke shelf, and a surround that hides the connection.
The fix: We pull the insert, clean the connector, smoke shelf and flue, and correct the connection so the next sweep can reach everything. Wood Stove and Insert Sweep, from $279
- Less common
Years of use with no one looking
The sign: A stove that came with the house, no memory of the last sweep, and a flue nobody has seen the inside of.
The fix: A Level 2 camera inspection measures how thick the glaze is and whether the tiles under it have already cracked. Chimney Inspection, from $129
Two minutes of safe checks
With the fireplace cold, these checks tell soot from glaze and show what has been feeding it.
- Shine a flashlight on the firebox walls and up past the damper: dull, flaky black is first degree soot, while a hard surface gleaming like black glass or dried tar is glaze.
- Look at the stove door glass or the insert surround: a brown film that returns within a day of cleaning means the fires are smoldering, and the flue is seeing the same smoke.
- Split a piece of your firewood and press a fingernail into the fresh face; wood that dents and feels cool inside is wet, whatever the stack looks like outside.
- Confirm a working carbon monoxide alarm is on the same floor as the stove or fireplace, because a flue choked with glaze sends combustion gases back the other way.
Why a sweeping brush will not take glaze off
Glaze is tar baked onto clay tile or steel, and bristles slide across it the way they slide across a varnished floor. A sweep is built for the flaky and crunchy stages, not this one.
| Degree | What it looks like | How it comes out |
|---|---|---|
| First degree | Dry, flaky black soot | Brushes out as black dust during a sweep |
| Second degree | Crunchy, tar-edged flakes | A stiffer brush or a rotary head |
| Third degree (glaze) | A continuous shiny skin, often with tar pooled behind it | A chemical modifier that turns it brittle over days, then rotary chains and scrapers down to the tile, often across two visits |
How Portland fires end up glazing a flue
Picture a wood stove or insert set into an older brick fireplace, venting into a cold, oversized and often unlined flue. The smoke cools and condenses before reaching the top.
East side neighborhoods such as Richmond, Sunnyside, Montavilla and Woodstock carry many of those chimneys, and an insert slid into one without its own liner is the surest glaze maker we know. The smoke shelf fills with tar first, then the flue above it.
Out in Sandy, Canby, Scappoose and Forest Grove, where a stove heats the house, the long, closed-down overnight burns of a wet winter do the same work. Dry wood and a hot morning fire each day help, though they will not remove what is already there.
What removing glazed creosote involves
The job runs in four parts, and the fireplace stays out of service until the last one is done.
Camera first
A Level 2 camera run records the glaze from smoke chamber to cap, measures its thickness and looks for cracked tiles or open joints under it. The images are yours, and they decide whether a liner is part of the answer.
The treatment
A creosote modifier is applied to the glazed surfaces and left to work, turning the tar into a crumbly layer that tools can bite into. The fireplace stays cold meanwhile.
Mechanical removal
With the opening sealed and a HEPA vacuum running, rotary chains or whips and hand scrapers take the broken glaze off the tile, the smoke chamber is cleaned, and the smoke shelf is emptied of pooled tar.
Stopping it coming back
The camera goes up again to confirm bare tile. Then the cause gets fixed: an insulated liner for a cold or oversized flue, a proper connection for an insert, and a change in wood and burn habits we walk through with you at the hearth.
Glazed creosote: common questions
Is black shiny creosote in my chimney the same as stage 3 or third degree creosote?
Yes. Shiny, tar-like or glassy black buildup is what the trade calls third degree or glazed creosote, the stage after flaky soot and crunchy flakes. It forms when smoke condenses on a flue that runs too cool, and it calls for removal work rather than a routine sweep.
Can I burn a creosote log or sprinkle powder to get rid of glazed creosote myself?
Not on a flue that is already glazed. Those products can soften light deposits, but lighting fires in a glazed flue to burn one is the risk you are trying to avoid, and whatever the product loosens still has to come out mechanically. Leave the fireplace cold and have the glaze removed.
Why is my flue glazed when I burn every day and get it swept every year?
Because glaze forms between sweeps, and a brush leaves it behind. Daily smoldering fires lay down tar faster than a yearly visit removes soot, and each sweep takes the flaky layer off a glaze that keeps thickening underneath. Hotter, shorter burns with dry wood turn the deposit back into the kind a sweep can handle.
Does shiny black creosote mean I have already had a chimney fire?
Not by itself. Glaze is unburned fuel sitting in the flue. A flue that has burned looks different: the creosote puffs up into gray, honeycombed or popcorn-like masses, the damper may be warped and tiles may be cracked. Seeing both the shine and the puffed material means a fire already happened, so book a Level 2 inspection.
Why is creosote dripping down the inside of my chimney like tar?
Dripping creosote is third degree creosote in liquid form. Smoke is condensing on cold flue walls faster than the next fire can bake it dry, so it runs down and pools on the smoke shelf or behind an insert. It is flammable where it sits, and the fix is removal plus a warmer flue, usually an insulated liner.
Will a stainless liner stop glazed creosote from coming back in my flue?
It helps most when the cause was a cold or oversized flue. An insulated stainless liner fitted to the appliance warms quickly and keeps smoke above the temperature at which it condenses as tar. It cannot overcome wet wood or fires that smolder all night, so liner and burning habits work together.
Related pages
Areas we cover for this
Calls about glazed creosote come in from Raleigh Hills and Garden Home, Tigard, Alberta Arts District and Concordia and every other part of the metro we serve.
Ready to book a sweep?
Call with what the fireplace is doing, or text a photo of the opening and one of the chimney top, and we will name the service and its posted price before we come out.