Block Chimney Repair

we're golden · 08-28-2009, 09:36 AM

I have a cinder block chimney that I believe was built in the mid 70's. I can see cracks in not only the seams, but also running through the blocks themselves. In the spring after the heavy rains, and entering the house after it has been closed up for the week, there is a strong ash smell. Can anyone recommend a product that I can apply that would seal the exterior of the chimney? Any help would be appreciated.

SIKSUKR · 08-31-2009, 08:18 AM

That strong ash smell probably has little to do with the condition of the chimney.My chimney is in great shape and I have the same issue on cold spring rainy days.What's happening is that heavy cold air is sinking down your flue.When heat is generated in the room with the chimney,the air will rise up the flue and you will have no smell.I used to have a much more frequent issue because of the negative pressure my forced draft furnace vent would cause from sucking the air out of the house.Easiest place to come in was down the chimney even with the damper closed.I did away the forced draft even after allowing for make up air right next to the furnace.Hardly have noticed any ash smell anymore.

we're golden · 08-31-2009, 11:04 AM

Thanks SIKSUKR that makes perfect sense!In your second to last sentence you said you did away with the forced draft by allowing for make up air right next to the furnace. How did you do this?

SIKSUKR · 09-01-2009, 12:02 PM

What I was refering to was the direct vent system on my furnace.Instaed of the usual chimney vented outlet,more and more systems have gone to a forced draft direct vent,meaning the exhaust can be vented right through the wall.It has a fan that creates the draft that is missing without the rising of hot air up through a chimney.That fan is sucking air out of the house which makes the pressure in the house lower(negative) than the outside(positive).Pressure wants to equalize so it finds a way to get into the house.The easiest way especially in the more modern well insulated homes today,is through a Chimney,even with the damper closed.What I did when I still had my forced draft system was to cut a vent in the wall next to my furnace and installed a small heat register louvered diffuser so the make-up air would come in right there and not through my chimney.The diffuser louvers could be adjusted to satify the make-up requirements.Not the most efficient way but it worked.Ultimately I removed the forced draft because of the noise it created(it was below my bedroom)and installed a metal insulated chimney.Works great.

08-28-2009, 09:36 AM	#1
we're golden Junior Member Join Date: Apr 2008 Posts: 13 Thanks: 10 Thanked 2 Times in 1 Post	Block Chimney Repair I have a cinder block chimney that I believe was built in the mid 70's. I can see cracks in not only the seams, but also running through the blocks themselves. In the spring after the heavy rains, and entering the house after it has been closed up for the week, there is a strong ash smell. Can anyone recommend a product that I can apply that would seal the exterior of the chimney? Any help would be appreciated.

08-31-2009, 08:18 AM	#2
SIKSUKR Senior Member Join Date: Apr 2004 Posts: 5,075 Thanks: 215 Thanked 903 Times in 509 Posts	That strong ash smell probably has little to do with the condition of the chimney.My chimney is in great shape and I have the same issue on cold spring rainy days.What's happening is that heavy cold air is sinking down your flue.When heat is generated in the room with the chimney,the air will rise up the flue and you will have no smell.I used to have a much more frequent issue because of the negative pressure my forced draft furnace vent would cause from sucking the air out of the house.Easiest place to come in was down the chimney even with the damper closed.I did away the forced draft even after allowing for make up air right next to the furnace.Hardly have noticed any ash smell anymore. __________________ SIKSUKR

09-01-2009, 12:02 PM	#4
SIKSUKR Senior Member Join Date: Apr 2004 Posts: 5,075 Thanks: 215 Thanked 903 Times in 509 Posts	What I was refering to was the direct vent system on my furnace.Instaed of the usual chimney vented outlet,more and more systems have gone to a forced draft direct vent,meaning the exhaust can be vented right through the wall.It has a fan that creates the draft that is missing without the rising of hot air up through a chimney.That fan is sucking air out of the house which makes the pressure in the house lower(negative) than the outside(positive).Pressure wants to equalize so it finds a way to get into the house.The easiest way especially in the more modern well insulated homes today,is through a Chimney,even with the damper closed.What I did when I still had my forced draft system was to cut a vent in the wall next to my furnace and installed a small heat register louvered diffuser so the make-up air would come in right there and not through my chimney.The diffuser louvers could be adjusted to satify the make-up requirements.Not the most efficient way but it worked.Ultimately I removed the forced draft because of the noise it created(it was below my bedroom)and installed a metal insulated chimney.Works great. __________________ SIKSUKR

08-31-2009, 11:04 AM	#3
we're golden Junior Member Join Date: Apr 2008 Posts: 13 Thanks: 10 Thanked 2 Times in 1 Post	Thanks SIKSUKR that makes perfect sense!In your second to last sentence you said you did away with the forced draft by allowing for make up air right next to the furnace. How did you do this?