Dose lime mortar have a life span?

[michael]

Just wondered, because I’m constantly having small bits of lime mortar falling down my chimney and depositing itself in the fire place.
The building is of brick construction (including the chimney stack ) built and expanded upon between about 1817 and 1880.
The chimney is unused and is capped of at the chimney pot with a ventilated terracotta cowl. The outside of the stack has been well maintained, repointed with lime and is in relatively good condition.
I’m rather hoping that the chimney stack won’t need rebuilding in my lifetime.

 

[MatthewC]

The Romans used lime mortar in their buildings. Where it remains, it has now fully calcified so it's as hard as rock - in fact it is rock, being solid calcium carbonate. So, there is no life on lime mortar, but it must depend on the conditions.

I would guess that your chimney has not always been ventilated, but has been subject to prolonged dampness at some time in the past. Once that happens it slowly crumbles. In my house we had many areas where the plaster on the walls and ceilings was just damp mush, if it still existed, due to prolonged water ingress. Elsewhere it was no longer wet but it had nevertheless lost adhesion with the stone or lath, or was just breaking into little squares, held together by hair. I would put all that damage down to dampness at some time in the past (assuming it was properly applied originally).

Matthew
http://houseintheenchantedforest.blogspot.com/

 

[stuart45]

It's probably only the parging which gets attacked from flue acids over the years.

 

[MdB]

The little original lime mortar / plaster I've found in our house is in a very poor state. The surface layer can be okish but anything beneath the surface just falls to pieces and can easily be hoovered up. I've no way of knowing if it has always been like this or has failed over time but I can fully understand why a previous owner has removed most of it.

 

[AMc]

We have a metal lined flue above the woodburner but prior to getting the register plate it would drop small bits of chimney stack into the hearth.
The other chimneys are capped but still deposit small amounts of mortar and brick. My guess is that wind loading and slight changes in moisture cause a little erosion but there is still a hell of a lot of brickwork still there.
I would also imagine that the better faces and better bricks would be used facing out and so the quality of brick lining the inside of a chimney may be lower than you might hope.
In short I'd try not to worry about it too much.

 

[Zebra]

Similarly, my chimney mortar was in a poor state, very crumbly, and I repointed in lime satisfactorily on the outside, but of course never can from the inside (I tried - I could get up there but couldn't manoeuvre the trowel!). So bits might well fall down. I wonder whether having the chimney swept might remove any loose stuff so that it doens't fall down at random times? Can't see any real advantage of this though, if the chimney's not in use.