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It's funny, we know that parging the interior of the flue is the Lexus way of doing it but in reality that's not always the case.

This is fireplace country - most homes here, new or old, have some kind of fireplace. Yet, it's extremely rare to see a fireplace throat or flue parged around here. I'd bet I only see it about one in every 2,000 fireplaces. Probably 30 - 40% of them - being more than 50 - 60 years old - don't have any tiles lining their flues either. Most don't have spark arresters or bonnets on them either.

Don't hear much about chimney fires though and, despite our famous dry climate, don't see a whole lot of damage being done by rain due to no covers. Do see a lot of damage caused by cracked/eroded crowns and full permeation of stacks though.

Regional differences/customs are interesting, aren't they? I should think that if I were to relocate to another part of the country I'd end up going through a rough patch wherein the way things are done in the new location seem pretty alien and incorrect to me.



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Back in 89 when I last worked in masonry, the smoke chamber was never parged on the interior and we never filled the cores either. The top most brick were positioned to support the clay flue around the full perimeter. We worked fast though, 2 laborers would set and load scaffolding the day before, then 1 laborer and 2 brickies would build from the basement to the cap and tear down the scaffold in about 7 hours.


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I might be mis-stating this, but NFPA would "condemn" anything that wasn't parged. The guidelines are rigorous and stringent.

If a sweep made a comment that it was dangerous, they would have the NFPA backing them up. If we said it was OK, we would be standing there with our pants around our ankles.

It becomes a problem when a sweep says it's bad, or when there's a house fire. Either way, you lose if you don't point it out first.

We're not in the business of taking bets or determining probabilities.

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  • 4 months later...

Hey guys. I might be late on the reply but i just picked up this site today. I see lots of bad bricklayers build the chamber/throat this way and it's sick. All those corbels are a nice place for cesote to stick and hang = chimney fire. This can all be fixed by people learning how to build a tree out of some plywood and 2x12. I'll post some pictures later on what this looks like if anyone is interested. I promise you end up with a nice smooth chamber/throat every time.

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  • 2 weeks later...

Around here, there are some chimney inspection guys that will "fail" a chimney/fireplace inspection for a corbelled throat. I guess it then becomes an issue.

Around here 99.9% of the chimney inspectors will fail any and every chimney long before they even get out of their trucks.

This from the NJ edition of the 2000 IRC;

R1003.8 Smoke chamber. Smoke chamber walls shall be constructed

of solid masonry units, hollow masonry units grouted

solid, stone or reinforced concrete. Corbelling of masonry

units shall not leave unit cores exposed to the inside of the

smoke chamber. When a lining of firebrick at least 2 inches (51

mm)thick, or a lining of vitrified clay at least 5/8 inch (15.9mm)

thick, is provided, the total minimum thickness of front, back

and side walls shall be 6 inches (152 mm) of solid masonry, including

the lining. Firebrick shall conform to ASTM C 27 or C

1261 and shall be laid with medium-duty refractory mortar

conforming to ASTM C 199. Where no lining is provided, the

total minimum thickness of front, back and sidewalls shall be 8

inches (203 mm) of solid masonry. When the inside surface of

the smoke chamber is formed by corbeled masonry, the inside

surface shall be parged smooth.

I don't have older additions so I don't know when it came into play, and not long back, this town adopted the code, that town still hadn't...

That being said, I very much share Mikes opinion on it. Very, very rare to see it parged, so the only time I will really "talk about it" is when I see evidence of a need to change it, like scorching/soot staining on the face of the fireplace, really horrendous creosote build up or deterioration I think I can attribute to the lack of parging.

If I remember correctly this is one of Bill's favorite rants, no comments Bill?

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  • 4 weeks later...

I did a house this morning for a client/friend who owns a Chimney Services company. I asked him about this specific issue, and since the cores are seldom filled around here, he said he didn't make an issue of it when he initially began his business.

Until that is . . . one of his customers had a chimney fire that spilled out and burned the mantel. The cause? Built-up creosote in open core bricks like in John's photo. Ever since, he's busted every fireplace he's seen that has open-core bricks inside.

The remedy is to apply refractory concrete, which apparently is a major pain in the arse, depending on how the damper is situated.

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