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Old 01/13/11, 10:46 PM
therunbunch's Avatar
Join Date: Oct 2009
Location: East Texas
Posts: 2,352
How to seal up hole in chimney where...

How to seal up the hole in chimney where the wood burning stove thing used to vent through...???

The house we are renovating has 2 chimneys. One is completely dead.. has nothing hooked up to it for the past half century. The 2nd.. currently has furnace (in the basement) hooked into it and vents upward and outward.

The home inspector told me we needed to concrete up those holes (now covered with round, about the size/shape of a dinner plate, cover) to make sure no fumes or carbon monoxide could escape into the room.

I guess they used to have wood burning stoves hooked up at them. I have the concrete.. just have NO idea how to mix it and definitely no idea how to concrete these holes up! I'm not too worried about the one in my dining room as it is not hooked up to anything and if I push concrete too far into it and it falls down the chimney base there is nothing it can really ruin. However, the one in our family room has the furnace hooked into it and I want to be sure no material falls down into that one.

How do I seal these things up? A friend of mine suggested putting some bricks in the holes and then concreting.. I should mention that once you move the cover plate.. it is like a metal or aluminum tube or whatever in the wall (about 8 inches in diameter) and then the drop off that goes down to the basement (through the chimney) or up to the roof. I hope someone understands my ramblin'!
A closed mouth gathers no foot.
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Old 01/14/11, 12:09 AM
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Join Date: Sep 2007
Posts: 24
You really should have it done by a certified Chimney Sweep. Check the CSIA website to find one in the area.
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Old 01/14/11, 12:11 AM
Bearfootfarm's Avatar
Join Date: Jul 2006
Location: Eastern North Carolina
Posts: 45,398
A friend of mine suggested putting some bricks in the holes and then concreting.
That would work, but you need "mortar" instead of conrete.

The difference is concrete has rocks in it, and mortar doesn't

The easiest way to mix it would be to get a "mixing tub" from Home Depot, Lowe's, etc, and a small masonry trowel.
Mix the mortar with just enough water so it's about the consistancy of mashed potatoes, and use the trowel to put about an inch in the bottom of the opening, a little wider than your brick, then lay a brick lengthwise in the mortar, pushing it down a little to set it in.

Keep the end of the brick back from the edge of the opening about 1/2 to 1 inch.

Fill in around and on top of the brick with more mortar, or pieces of brick and repeat the process with more bricks. Don't worry about how it looks as long as the openings are sealed.

When you get near the top you may have to use pieces of brick to fill in odd spots.

Once you get it closed off, use the trowel to throw mortar onto the ends of the brick to fill up the gap at the end, and then smooth it off evenly.

When its nearly set, you can brush it with a paint brush and some water to get a very smooth finish

Take your time and it won't be as complicated as it sounds
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Last edited by Bearfootfarm; 01/14/11 at 12:14 AM.
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Old 01/14/11, 02:40 AM
Join Date: May 2006
Location: north central wv
Posts: 2,321
Are you sure you will never want to hook a wood stove or anything else to it? If it is drawing it will never leak anything into the room. Sam
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Old 01/14/11, 03:43 AM
||Downhome||'s Avatar
Born in the wrong Century
Join Date: Jan 2009
Location: Michigan
Posts: 5,431
as a former furnace installer you need chimney cement, leave the the cap it should be a cap at least, same as you would use to cap off a duct pipe of the diameter.

the cap you have should look something like this
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Old 01/14/11, 10:25 AM
Join Date: Dec 2002
Location: East TN
Posts: 6,977
I'm guessing this is a brick chimney with a clay liner???

If the chimney is brick with a liner you should fill the hole with brick. You can't just shove cement or mortar in a hole that big as it will just fall in. I would do all I could to do it correct and not mess up 2 good chimneys.
I would get a few similar bricks and cut them to fit. Butter them with mortar and stcak in the hole. When they are in and dry you can go back and fill the joints nicer or smear mortar over them to finish.
"Education is the ability to listen to almost anything without losing your temper or your self confidence"
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Old 01/14/11, 01:05 PM
Join Date: Jun 2002
Posts: 5,964
I disagree with covering over the hole in the "dead" chimney. (I would make sure the top is covered - to keep precipitation, birds, insects, etc out), but your "dead" chimney could be a great hiding place for your valuables.

As for your other chimney, as long as the cover is in place, I can't see where fumes would be a problem.
Michael W. Smith in North-West Pennsylvania

"Everything happens for a reason."
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Old 01/14/11, 04:08 PM
Join Date: Dec 2010
Location: Central Oregon
Posts: 6,327
If it is not a huge hole, there is an expanded metal mesh that is made for mortar. You fasten that over the hole and cover it with mortar.

They will sell it an any place that sells brick or stone facing.
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Old 01/15/11, 10:55 AM
Join Date: Jul 2007
Location: Western New York
Posts: 2,026
Dead chimney - I'd hang a work light from the top & stick my head in the vent hole or a mirror or a video cam and do a quick inspection. If it's in good shape I'd save the chimney. A wood stove is a great add on for resale and a awesome homesteading tool.

~~ pelenaka ~~
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