Seen that Black Stuff in Your Chimney? That’s Glaze & you Should Know What it Is
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  • Seen that Black Stuff in Your Chimney? That’s Glaze and It’s Important to Know What It Is

    Seen that Black Stuff in Your Chimney? That’s Glaze and It’s Important to Know What It Is


    If you have a fireplace in your home, there’s a good chance you’ve heard all about the dangers. You might already know about the potential hazards of carbon monoxide poisoning, and you’ve probably even read up a bit about creosote. If you see black buildup in your chimney and you’re not sure what it is, it could be glaze – and that could be a problem. Here’s what every homeowner with a fireplace should know about chimney glaze.

    What Is Creosote, Anyway?

    Most homeowners who have and use fireplaces know that creosote is dangerous, and unfortunately for many, that’s where their knowledge ends. Specifically, creosote is a byproduct of the combustion process; it is released and travels up through your chimney with each fire you light. Over time, creosote builds up, and the more of it that lines your chimney interior, the more flammable it becomes. When you call a professional chimney sweep to clean your chimney, their primary concern – even above aesthetics – is removing the buildup of creosote.

    Three Levels of Creosote Buildup

    Creosote is an interesting compound in that it can change forms over time the longer it builds up. There are actually three different levels that every homeowner should know about.

    • Level 1 – At this level, creosote is powdery, sooty, and relatively easy to remove. Chimney sweeps can simply brush it away.
    • Level 2 – By level 2, the creosote has moved past this powdery phase and become a hard, glossy substance that must be chipped away from the chimney liner in flakes. It is much more difficult to remove now, so rather than a typical brush, chimney sweeps rely on power tools to get it off.
    • Level 3 – Level 3 is the worst and most dangerous creosote level. By this point, the creosote has built up to the point that it becomes thick like tar, and it may even start to drip like honey as it warms up. This is known as “glaze” and it creates a serious fire hazard in your home.

    What Makes Creosote Glaze?

    There are a couple of different things that can cause creosote to glaze inside your chimney. The first, of course, is the failure to clean your chimney regularly as you light fires. Over time, the buildup changes form and texture, ultimately resulting in level 3 buildup. Glaze also occurs when creosote accumulates in the chimney before all the previous layers have had the chance to dry. Things that can cause this include a flue that isn’t the right size, burning green and/or unseasoned wood, and allowing fires to smolder at low temperatures for long periods of time.

    How to Remove Glaze

    Homeowners should never attempt to remove glaze on their own; at this point, the substance has dried to the liner and must be removed with chemicals – often very acidic chemicals that are dangerous to handle without the proper tools and experience. In the very worst cases, it may be necessary to completely remove and replace the chimney liner. This may seem like overkill, but it is important to remember that creosote can damage the liner itself and destroy the underlying chimney masonry, too.

    Ideally, the best way to handle glaze is to prevent it in the first place. Scheduling regular cleanings once a year (or every 36 or so fires), burning only completely dried and properly seasoned wood, and putting out any fires promptly rather than allowing them to smolder are the best prevention tips.  Contact us today to schedule your next chimney service appointment.


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