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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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Housing - Renovation: Pointing / Decaying Masonry

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    Can anyone help? I am new to the forum and have little to no knowledge of masonary repairs.
    I live in a c200 year cottage in Chester which was re-pointed in 2003. I have noticed on my south facing wall that the mortar below the backdoor threshold has totally decayed / crumbled. I think when it rains that the water collects at the back door and hence makes the mortar weak? It appears that the mortar that has crumbled is below the PVC damp sheet but in a few areas it appears the mortar above the pvc membrane is wet.
    How can I repair this issue? Is it normal for the mortar to decay below the damp proof PVC Membrane line as I guess with the house being so old the mortar is a lime mix? If so, what does this mean about the condition of the foundations?
    Any help / advice truly appreciated.
    • CommentAuthorRoger
    • CommentTimeAug 2nd 2007
     
    Hi.

    You probably want to have a look at http://www.periodproperty.co.uk/discussion_forum.htm where there is a great deal of expert comment on this subject.

    Roger.
  3.  
    Where you will probably get comments like:
    It sounds as though there was something wrong with whatever was used in 2003 as the repointing should have lasted a very long time. A 200 year old house would certainly have had lime mortar - Ordinary Portland Cement not having been invented. Repoint with a 1:3 mix of hydrated lime and sharp sand above the dpc. Below the dpc you might be justified in using a hydraulic lime. Definately no cement.
  4.  
    Thank you for your help. Just for the sake of clarity. Given the house age of 200 years and therefore lime mortar has been used, does this mean the foundation mortar is decayed / crumbled? What sort of foundations did houses of this age get built on? Should I be concerned?
    I have not noticed any crack / subsidence but when I went to mount and external light about half way up the wall when I drilled into the mortar it was very easy (not damp) unlike when you drill cement mortar it is harder to drill. Is this because the mortar is a lime mix and therefore easy to drill?
  5.  
    Yes, lime mortar is very easy to drill holes in. 200 year old houses often had little that a modern Building Control Officer would recognise as foundations but, curiously, they stay up for 200 years. One of the many advantages of lime mortar is that it doesn't crack when there is some movement in the building. The calcite crystals can break and recrystallise within the mortar so that significant movement can be accomodated without threatening the building's structural integrity. So don't be concerned that your house has no foundations as they are really only required when building with cement.

    Cement is such useless stuff in comparison with lime.
  6.  
    Thank you again. Great help and a great site.
    Cheers

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