Thread: Chimney Stains - Comments Needed

This is a chimney for a wood burning prefab fireplace. The house is 30 years old. The chimney cap is very rusted and has no overhang.

I am looking for a bit of help commenting on the dark stains on the exterior of the chimney chase below the chimney cap. Could this possibly be caused by a disconnected chimney section inside the chase?

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Looks like a combination of rust streaks and possibly soot or rust streaks and fungal growth. The metals tend to inhibit fungal development so I would be inclined to go with the soot.

I do not think that a disconnected flue trying to leak out of the metal cap flashing would cause the streaks to run down. I would expect they would streak upward.

This is not an indication of a dislocated chimney pipe. I have attached photos that depict a dislocation. What else is wrong with this chimney system?

1) soot pushing out from under the cover.
2) Termination cap at cover.
3) Soot deposits within the wood framed chase area.
4) Termination removed with soot on exterior surface due to dislocation.

“Partners in Education”

Dale,

So do you think the discoloration on the chimney that I posted is rust staining?

Time for a Level 2 inspection Bruce.

Sure looks like it, Nick.

looks more like moisture staining and the corner,stucco, appears to be failing. The metal cap should have covered the entire chimney.

The chimney chase is toast. 99% chance that the wood supporting the stucco is rotting. The cap has not protected the chase and water has entered it. I think the stains are a combination of rust, soot, and tannins from the rotting wood.

That's an interesting thought, Scott. I had not thought of tannins.

The stucco is deteriorating at the corners of the chimney chase (with the metal lath exposed) and below the chimney cap. A lot of this damage could have been avoided had the cap overhung the chase. Unfortunately the stucco color coat was installed over the cap which allowed water to flow into and behind the stucco. Poor workmanship and a lack of attention to detail.

The stains are from combustion byproducts, most likely. A more in-depth evaluation and cleaning by a chimney sweep would be in order. When was the last time the flue was cleaned and inspected? How does this chimney sit in relationship to prevailing winds?

Originally Posted by Randy Aldering

The stains are from combustion byproducts, most likely. A more in-depth evaluation and cleaning by a chimney sweep would be in order. When was the last time the flue was cleaned and inspected? How does this chimney sit in relationship to prevailing winds?

Yes, that is a possibility but!! The darn chase is falling apart! The entire things needs to be replaced.

The reason a drip edge is installed on a chimney is to prevent just such an occurrance. Water draining off the cap with creosote and carbon deposits in it runs onto and inside the chimney structure. Yes more than likley plywood underlayment deteriorated , etc, etc. Typical snowball effect.

I think we might be jumping to some conclusions. Remember that it is not the stucco that provides the weather barrier, but the paper beneath. If the moisture was making its way through the weather barrier and into the wood framing, then there would be indications of expansion (vertical cracks in the stucco finish as the upper wood expands). I do not see this evidence. I see very limited damage and the damage I see is to the stucco applied directly to the sheet metal. I would expect the stucco to fail. The installer simply used the chase cover as a stucco stop. Poor job, yes? Damage to the wood is very doubtful. I have opened thousands of these chases and truly understand these concerns. However, I do not believe this is one of those concerns.

The stains are from use and exposure. I agree that it is time to replace this cover. You should recommend a minimum 4” vertical drop that (as stated) covers the entire stucco application. I also recommend a full Level II based on the age of this unit. According to the termination cap, this system is over 25 years of age. These systems typically have a 25 year LIMITED warrantee. Its past due for a professional inspection by a certified inspector.

Fuel for thought