Lime mortar + bad weather = house falls down?

[sarahj]

See this link:

http://news.bbc.co.uk/1/hi/england/tyne/7607127.stm

is there cause for concern for anyone else?

 

[MdB]

Interesting question. Does set lime mortar weaken when it gets wet?

I've had a quick google and can't find the answer. I would assume not and that there is something else going on in this collapse. The obvious question is why did it get wet?

 

[Nemesis]

It was repointed about four years ago - in cement.

Cement = trapped mosture = saturated walls. Also = wall falling onto neighbour's BMW.

The coping stones possibly also were not totally sealed (flat stones laid edge to edge, and probably not laid as would be done now on a lead sheet to satisfy building regs) and water could enter the wall from above.

http://www.chroniclelive.co.uk/north-east-news/todays-evening-chronicle/tm_headline=pensioners-home-wrecked-in-floods-aftermath&method=full&objectid=21709492&siteid=72703-name_page.html

Note also the flues running through the wall, making another weak point.

 

[Pford75]

Does set lime mortar weaken when it gets wet?

Not commenting on the couple's house in question, I believe that lime mortar does weaken when it gets wet.

Forum regulars will have been bored to tears over recent months with the rebuilding of my flint wall. However, more recently, another section of the wall has been suffering. A developer on the other side of the road has disconnected pipe which ran from the storm drain on the highway. The resulting impact is that every time it rains, we have a huge (and I mean huge) puddle. This covers one side of the carriageway and is sufficiently deep that it is deeper than kerb height and covers the footpath.

Every vehicle passing through (and there are probably 500ish a day) sends a splash of water over a section of the flint wall. This has occurred for apx. 6mths+ whilst Highways have been navel-gazing and trying to work out what to do. The latest consequence is that several flints have dislodged themselves and the mortar has returned to the consistency of wet sand. It would be relatively easy to remove flints from the waterlogged section with my fingers! So, I'm now waiting on a response from the County Council...since I can't repair the damaged section until the drains are fixed.....and i'm also going to be asking the developer to repoint the section of waterlogged wall. Incidentally, the next panel along (which has not been soaked), the mortar is hard and the flints are secure.

 

[Lime]

I suspect that the lime - sand mix may have something to do with being soft too.
From the pictures it looks as though the chimney stack came down first pulling the skin of the wall with it.
Perhaps it was the wind that caused the fall?

 

[biffvernon]

There is absolutely no reason why lime mortar water should be damaged if it gets wet. That's why it's been used for building houses in rainy countries.

 

[Nemesis]

The houses in question are built in a system (as with other houses in the area) of an inner skin of rubble and an outer skin of dressed stone. The mortar is in general soft and the inner rubble has more mortar, the outer stones are quite well dressed and fitted (softish sandstone) so have very little.

The inner 'gap' is filled roughly as the building is erected, with mortar.

Flues run through the walls, making weak points. Over time, what mortar there was in the flues gradually vanishes. The tops of the walls (I know Theresa Street) have flat coping stones as covers, rather than having the slates run over to cover the walls.

Water can easily get down between the gaps in the coping, which in turn can saturate the walls. Hard cement pointing won't allow it to escape, although it may be that damp would appear on the inside too.

While the chimney could have fallen, in general they are built as a separate item, not as one with the gable, with a coping stone running under the gable side and built from large thin section sandstone regular blocks (at times replaced with brick, and often reduced in height when gas fires became the norm). If they fail, they tend to simply fall away from the building. Not a frequent happening, mostly gravity and habit hold them together.

 

[Gareth Hughes]

It was repointed about four years ago - in cement.

Andrew Howard, from Gateshead Building Control, said: “It was a freak accident caused by the non-stop recent rain saturating the lime mortar in the wall.

“The mortar will have just got heavier and heavier until the whole wall collapsed under the weight.

Badly misreported by both the BBC and the local paper, on the basis of a (presumably) off the cuff quote.

I await the first Listed Building Consent application to replace lime with cement because lime makes your house fall down. (to accompany the various queries about replacing thatch with tiles because "thatch catches fire")

 

[Schoolmarm]

Does set lime mortar weaken when it gets wet?

The latest consequence is that several flints have dislodged themselves and the mortar has returned to the consistency of wet sand. It would be relatively easy to remove flints from the waterlogged section with my fingers! So, I'm now waiting on a response from the County Council...since I can't repair the damaged section until the drains are fixed.....and i'm also going to be asking the developer to repoint the section of waterlogged wall. Incidentally, the next panel along (which has not been soaked), the mortar is hard and the flints are secure.

I feel that your mortar hasn't set and has, in fact, just dried out.

 

[Welsh Builder]

Nemesis is 100% right.

Re-pointing in lime would have save the wall. Re-pointing in cement has trapped moisture and caused it to fail.