Problem with ceiling near chimney

My [COLOR=blue !important][COLOR=blue !important]chimney[/COLOR][/COLOR] goes up thru the middle of my ranch house. I have been having flaking and a yellow stain on the ceiling, right where it joins the chimney. I thought it was the warm air going thru a air leak and causing condensation with the cold air of the chimney. It was better in the summer, but it is starting to get cold again, and is starting to flake again. Last spring I went up in the attic and sealed the metal flashing against the chimney, but the problem comes back.
Now up in the chimney, The rafters go around the chimney, but has a 1-11/2 inch space around the chimney, ..some (half around) has the metal flashing against the chimney, that I sealed. But, the other section, just goes all the way to the cellar.
Since the rafters (wood) does not go all the way around, I think the air is still mixing and causing condensation.
Can I box in the chimney with 2x4s or 2x6s and throw insulation inside, and then seal that up?? Or will that cause more problems.
I am getting frustrated.
I will try to post pics.
Thanks, Barry

Welcome to the site.
I think you have found the problem and I am not sure how to fix it. This is also a firestop problem as a fire in the cellar would have a free run to the attic.
There might be better ideas but I think you could fit a non combustable material tight to the chimney and fire seal it and then insulate, (concrete board) and then do the same at the cellar.

Yep maybe concrete board sealed in with Fire Foam.

Where would I put the concrete board??..on the ceiling around the chimney??..that is the concrete board you use for shower walls, correct??

I believe 'Old Dawg from another sister site has your best answer...

You have three possible scenarios going on. You have a leak from the crown of the chimney where the flue exits or you have a flashing issue around the base of the chimney either step flashing or counter flashing improperly installed or you have water leaching through the mortar joints of the brick. Caulking from the inside should never be done. You are not preventing water intrusion, you are trapping water. Insulating the chimney is a waste of money and time. Make sure you have a proper vent system to get rid of moisture and address the water issue from the source. That will be outside.

And then this...

If it's a condensation issue, you should see moisture collecting on the bottom of the roof sheeting. I've never encountered condensation solely on the chimney. If you see white chalking on the brick, that is effervescence and it's the result of water leaching through and leaving salt deposits.

havasu said:

I believe 'Old Dawg from another sister site has your best answer...

You have three possible scenarios going on. You have a leak from the crown of the chimney where the flue exits or you have a flashing issue around the base of the chimney either step flashing or counter flashing improperly installed or you have water leaching through the mortar joints of the brick. Caulking from the inside should never be done. You are not preventing water intrusion, you are trapping water. Insulating the chimney is a waste of money and time. Make sure you have a proper vent system to get rid of moisture and address the water issue from the source. That will be outside.

And then this...

If it's a condensation issue, you should see moisture collecting on the bottom of the roof sheeting. I've never encountered condensation solely on the chimney. If you see white chalking on the brick, that is effervescence and it's the result of water leaching through and leaving salt deposits.

Click to expand...

This might be correct but the fact that warm moist air can travel from the cellar and mix with cold air in the attic would cause condensation at this spot and this should be dealt with anyway.

Lets make this easy... stuff some fireproof Roxul brand or another.. no foam!! insulation around your area of the chimney..and be done.
This will fix the condensation from the metal firestop that is already there..

https://www.google.com/webhp?sourceid=chrome-instant&ion=1&espv=2&ie=UTF-8#q=fireproof insulation

BarryJ said:

Where would I put the concrete board??..on the ceiling around the chimney??..that is the concrete board you use for shower walls, correct??

Click to expand...

In your photos, we see a void and framing, fibreglass insulation in the void, full but not compacted. Strips of concrete board wide enough to screw down on top of the framing and fit snug to the chimney.seal that to the chimney and make sure there are no leaks anywhere from that cavity, check the gaps in the framing too. The same should be done in the cellar for fire stop.

nealtw said:

In your photos, we see a void and framing, fibreglass insulation in the void, full but not compacted. Strips of concrete board wide enough to screw down on top of the framing and fit snug to the chimney.seal that to the chimney and make sure there are no leaks anywhere from that cavity, check the gaps in the framing too. The same should be done in the cellar for fire stop.

Click to expand...

Neil??.. I dont see any insulation against the chimney? That is where I see some metal firestop, caulked with firecalk.
If you do not stop the temp Differential on that piece of metal, you don't fix the issue.
If there is no water leaks from above this spot.. that should be the problem you are having.
Also. if you do not have an Exterior chimney cap, water may be finding it's way through the interior of the chimney, and scaling... I think someone already mentioned this though..

inspectorD said:

Neil??.. I dont see any insulation against the chimney? That is where I see some metal firestop, caulked with firecalk.
If you do not stop the temp Differential on that piece of metal, you don't fix the issue.
If there is no water leaks from above this spot.. that should be the problem you are having.
Also. if you do not have an Exterior chimney cap, water may be finding it's way through the interior of the chimney, and scaling... I think someone already mentioned this though..

Click to expand...

The flashing does not close the whole cavity, they just put in enough to cover what the inspector could see from below.Is safe and sound rated for fire stop?
We don't know how hot the chimney gets.

Second photo looks like traces of effervescent.