[Cob] lime mortar

[Kathryn Marsh]

Their properties are different Bob. Lime mortar does need more  
frequent repointing to stay watertight but will last well so long as  
the pointing is done right - i.e. it is finished so that it sheds  
water. Cement will last longer but because it is a more complete  
moisture barrier you can get all sorts of problems from condensation  
build up inside the walls to moisture going through the stone instead  
of through the mortar. This can lead to flaking of the stone. Its a  
real problem round here where many walls are built of the local  
limestone beach stone. They lasted for centuries with lime mortar  
which "breathed" but from about 1920 onwards, and particularly from  
the 60s on, people have repointed them with cement and found that  
houses which had been dry since the middle ages are now really damp.  
And more seriously that the stones themselves are breaking up as  
moisture builds up in them

kathryn

On 10 Jan 2009, at 06:19, Bob Smolen wrote:

> Last fall, I started gathering old foundation rocks for my cob  
> project. At two sites,only the 8ft stone stem wall was standing  
> where a barn once stood. It was probably 110 years or older. I was  
> able to knock down the wall by pushing on a leaning section. I did  
> not really look at the foundation but the owners commented that the  
> wall came down easy because of the mortar used in the old days. I  
> believe he said it lacked cement which means it must have been lime  
> mortar. Is this an indictment of a non cement mortar? I know the  
> wall was subjected to years of weather unprotected so  maybe  
> deterioration should be expected. On the other hand, I dont think  
> the weather would have affected cement mortar. ( I did not notice  
> the foundation wall. It may have heaved after the roof of the barn  
> was off allowing moisture under the footer causing frost heave).
> Is lime mortar as good or close to as good as cement mortar for  
> buiding stone walls?
> Thanks,
> Bob
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