Pointing with lime

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Sheena Smart

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I live in a 150+ year old granite house which had suffered from poor cement pointing from a previous owner. As water had been penetrating the gable end I set out to have this re-pointed using lime as everything I had researched heavily supported the use of lime on a granite building. I am also conscious of the environmental impact of using cement. Having found a builder who agreed to point in lime and with my having provided the lime it has now transpired that he has been lobbing cement in along with the lime which is not what was agreed. When challenged he suggested he didn't believe it would do any harm but also revealed he had never worked with lime before even though this was a pre-requisite and fundamental part of our agreement. To say I'm disappointed would be an understatement but wonder if anyone can advise on problems, etc with mixing lime and cement and whether this interferes with the very qualities lime provides on a granite building and whether anyone has experienced similar problems?
 
You shouldn't put portland cement with hydraulic lime. The key thing with mixing is to mix it up in the mixer for about 20 minutes, then leave it for about 20 to fatten up, then mix up again for a few minutes.
 
problem I have is that he has mixed cement through the lime and I just don't know that it's going to be fit for purpose! He totally ignored me when I said I didn't want cement being used and lobbed it in the mixer although that was 2 days in, I was at work when he started the pointing. I don't know whether I should stop him from doing any more work??! Do you know what problems I may have with cement having been added to the lime??
 
As above the cement is unnecessary, but whether it will damage the granite is impossible to say for certain. I have certainly known granite and limestone stone walling pointed for many years in hard sand:cement where no damage resulted. On the other hand I do know one or two that showed signs of damage after less than 20 years. The fact is it depends on many factors that all need to come together. You say the granite was previously pointed in sand:cement. How long was that in place for and did it cause physical damage?
 
Builders not schooled in the art of lime tend to think of it as just something you add to cement mortar. Do you know what ratios he used? May be less problem with granite than with a soft limestone.
 
Limewash said:
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I spoke with the builder today - he claims he used one-part cement to 3 parts lime, I also suggested he cease work and we reconvene at the start of the week to see how we move forward and he has agreed this is sensible. I have also e-mailed Scotlime.org to try and get an understanding of the overall benefits of lime mortar. For my part it was primarily longevity and also aesthetics as part of my property still retains some original lime pointing which would be in excess of 150 years old - that in itself I felt presented a strong argument for its use. I am also trying to understand why builders prefer to use cement compared to lime - it continues to baffle me.

The cement pointing I am seeking to eradicate was possibly poorly done originally and while I cannot be sure when this was done as it was before I owned the property but would suggest it had started to crack within around 20 years. Unless a lottery win is heading my way I cannot afford to undertake this work again within 20 years or so.
 
Apart from aesthetics, the main issue of lime or cement pointing is that stonework joints ideally need to breath to allow water to permeate and evaporate from the surface. That's not to say cement doesn't breath at all - it does - but lime mortar is more breathable so allows this process more freely. In severe conditions hard cement pointing can cause physical damage to the stone itself. Water tries to permeate around the edges of the pointing and through the edges of the stones, which in some types of stonework can cause the stones to deteriorate quite rapidly. Note that pointing is really considered to be sacrificial in these circumstances - i.e. it is better for the pointing to deteriorate quickly than the stones!

Granite is less susceptible to this type of damage and the fact that you have had cement pointing for many years with no apparent physical damage probably means you won't suffer this problem. So you did the right thing and it is disappointing that it hasn't gone to plan but this isn't going to cause major damage to your stonework.

Incidentally, many people ask whether they should remove old cement mortar. EH advice is that this usually causes more damage than it solves and they normally advise against it. Of course your mortar won't be that hard yet so it might be slightly different but even so, I'd only consider it if it really does look awful and it comes out very easily without the use of machinery. Otherwise my advice is as before, continue with lime mortar but leave what's been done and don't over worry about it.
 
Firstly many thanks to everyone who's offered up advice thus far. I followed the advice above and e-mailed Scotlime who very kindly responded today and offered advice on my situation.

My overriding concern I suppose is 2-fold - firstly I entered into a contract with a builder who agreed to point the gable end in lime mortar which I provided, this is a breach of contract. As I am now aware of the fact he has used cement if I were to accept this modification and experience problems in the future I would likely have difficulty pursuing the builder at a later date. I therefore think my only way forward is to have what has been done removed and replaced with lime as was originally requested as, at the end of the day, it's my money and I'm the one who has to live with it - not the builder.

From my experiences of cement pointing on lime I am not convinced it works. When the cement pointing was removed the lime behind was damp and claggy and I firmly believe this was because moisture had no means of escape. I'm not a builder but it makes sense to me that this is why I was experiencing so many problems with dampness on the internal plasterwork.

I accept people appear to have differing views regarding cement but from what I can gather the property (apart from the east facing gable end which still retains its original lime mortar which is likely around 150 years old) was pointed in cement around 20 or so years back and had started cracking and showing signs of wear a few years back - for me that's not a durable product. While the former cement pointing was from a previous owner so cannot comment on how the work was done - I'm not sure I'm prepared to take the risk.

I cannot be sure how my builder will react when I advise on my decision but think I have to take the view that he has created a material breach of contract which must be rectified at his expense in order to fulfil his contractual obligations to me.

I am quickly learning that nothing is 'simples' when dealing with the building trade!!!!
 
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