Anyone know the current BRE stance on mixed OPC and lime mortar?

They were dead against it a few years ago.

I can't find my copy but I believe its this one, dated 2005
http://www.bsi-global.com/en/Shop/Publication-Detail/?pid=000000000030139915

Jon said >It may be worth your while reading about the subject if it interests you.

Here are a few of the online articles I've read over the last few years. Perhaps everyone should follow Jon's suggestions and do a little reading before continuing this debate.

Graham O'Hare, Lime Mortars and Renders: The Relative Merits of Adding Cement; http://www.buildingconservation.com/articles/cement/cement.htm
Peter Ellis, Gauging Lime Mortars; http://www.buildingconservation.com/articles/limegauging/limegauging.htm
Bob Bennett, The Development of Portland Cement; http://www.buildingconservation.com/articles/prtlndcmnt/prtlndcmnt.htm
Jonathan Taylor, Lime: The Basics; http://www.buildingconservation.com/articles/limebasic/limebasic.htm
John Ashurst, The Technology and Use of Hydraulic Lime; http://www.buildingconservation.com/articles/lime/hylime.html
Ian Constantinides, Traditional Lime Plaster: Myths, Preconceptions and the Relevance of Good Practice; http://www.buildingconservation.com/articles/plaster/plaster.htm
Ian Pritchett, An overview of buildinglimes; http://www.ihbc.org.uk/context_archive/54/overviewlimes_dir/overviewlimes_s.htm
Mike Wye, Hydraulicity in lime mortars; http://www.ihbc.org.uk/context_archive/63/limemortars/hydraulicity.html
Pat Gibbons, Pozzolans for Lime Mortars; http://www.buildingconservation.com/articles/pozzo/pozzo.htm
English Heritage, AC1 Smeaton project on historic mortars durability; http://www.uvm.edu/histpres/203/eh/RESEARCH1.HTML
Jeanne Marie Teutonico et al., The Smeaton Project: Factors Affecting the Properties of Lime-Based Mortars; http://www.jstor.org/pss/1504464 (sub required)



And in case you miss it, here are a couple of paragraphs from Graham O'Hares' paper which just caught my eye:

"DISADVANTAGES (of guaging lime with OPC)

•the rapid setting time limits the time available to the user in which to work with the gauged mortar
•some cements contain appreciable amounts of soluble salts, in particular potassium sulphate, which may become a source of salt damage to stonework
•the use of cement tends to lead to the user treating the gauged lime mortar as if it were a fully hydraulic lime or cement. Too much reliance on the initial chemical set leads to neglect of the importance of the longer term carbonation of the non hydraulic component present
•the danger that segregation occurs, whereby the cement separates from the lime as the mortar dries and hardens.

"Segregation is a major hazard of gauging lime mortars with cement. As the mortar sets, the cement colloid tends to migrate into the pores of the lime mortar as they form, clogging them and leading to a greatly reduced porosity. If the proportion of cement is high enough, segregation is much less likely to occur, but the resulting mortar will be hard. If the cement proportion is low, the mortar will be less hard, but segregation is more likely to occur. The resulting mortar will be seriously weakened, with a poorly formed pore structure leaving it very susceptible to frost damage and deterioration, even after carbonation of the non hydraulic lime present has taken place.

"The Smeaton Project, a research programme commenced by English Heritage indicates that a 1:1:6 mix, containing a 50 per cent cement binder, is unlikely to segregate, while a 1:2:9 mix, containing a 33 per cent cement binder, is almost certainly at risk. Until recently it was considered good practice to gauge lime mortars with as little as 5 per cent cement, just enough to impart a chemical set but not enough to make the mortar appreciably harder. However all of the Smeaton Project test samples containing less than 25 per cent failed.

"Given the possible hazards of segregation, an un-gauged lime mortar relying solely on carbonation is likely to be more resilient in the long run than one gauged with a small amount of cement. This will require care in its application and careful nurturing to ensure that it carbonates properly. If a chemical set is required, a safer alternative would be to use an hydraulic lime. In these the hydraulic components are so closely associated with the non hydraulic that segregation does not occur. These tend to be hard and impermeable, but not usually as hard as a 1:1:6 mix. Brick dust is a cheap and highly effective pozzolanic additive, providing a useful alternative to cement."

Posted By: biffvernonJon said >It may be worth your while reading about the subject if it interests you.

And in case you miss it, here are a couple of paragraphs from Graham O'Hares' paper which just caught my eye:

"DISADVANTAGES (of guaging lime with OPC)

•the rapid setting time limits the time available to the user in which to work with the gauged mortar
•some cements contain appreciable amounts of soluble salts, in particular potassium sulphate, which may become a source of salt damage to stonework
•the use of cement tends to lead to the user treating the gauged lime mortar as if it were a fully hydraulic lime or cement. Too much reliance on the initial chemical set leads to neglect of the importance of the longer term carbonation of the non hydraulic component present
•the danger that segregation occurs, whereby the cement separates from the lime as the mortar dries and hardens.

"Segregation is a major hazard of gauging lime mortars with cement. As the mortar sets, the cement colloid tends to migrate into the pores of the lime mortar as they form, clogging them and leading to a greatly reduced porosity. If the proportion of cement is high enough, segregation is much less likely to occur, but the resulting mortar will be hard. If the cement proportion is low, the mortar will be less hard, but segregation is more likely to occur. The resulting mortar will be seriously weakened, with a poorly formed pore structure leaving it very susceptible to frost damage and deterioration, even after carbonation of the non hydraulic lime present has taken place.

"The Smeaton Project, a research programme commenced by English Heritage indicates that a 1:1:6 mix, containing a 50 per cent cement binder, is unlikely to segregate, while a 1:2:9 mix, containing a 33 per cent cement binder, is almost certainly at risk. Until recently it was considered good practice to gauge lime mortars with as little as 5 per cent cement, just enough to impart a chemical set but not enough to make the mortar appreciably harder. However all of the Smeaton Project test samples containing less than 25 per cent failed.

"Given the possible hazards of segregation, an un-gauged lime mortar relying solely on carbonation is likely to be more resilient in the long run than one gauged with a small amount of cement. This will require care in its application and careful nurturing to ensure that it carbonates properly. If a chemical set is required, a safer alternative would be to use an hydraulic lime. In these the hydraulic components are so closely associated with the non hydraulic that segregation does not occur. These tend to be hard and impermeable, but not usually as hard as a 1:1:6 mix. Brick dust is a cheap and highly effective pozzolanic additive, providing a useful alternative to cement."

Biff, rather a selective quotation that, perhaps you need to take Jon's advice as well To put your quote into context, this, from the same 'paper'

''There are, as one would expect, both advantages and disadvantages in gauging non hydraulic mortars with cement to make them hydraulic.

ADVANTAGES

•it imparts a chemical set which occurs before full shrinkage occurs, thereby reducing the risk of cracking

•layers may be built up more rapidly, without the need to wait a long time for one to set fully before applying the next

•it hardens rapidly, thereby providing protection from rain before carbonation has been completed. This helps to beat the inclement British weather

•being an artificial substance manufactured under closely controlled conditions, it is reliable and predictable in use

•it is available in a choice of colours, useful when it is necessary to match the colour of an existing mortar or render. ''


The other references you offer seem to relate to historic buildings, and I do agree with you in that the wrong kind of OPC mix can be detrimental to historic fabric.

However, this does not mean that it is unacceptable to use OPC persay. Indeed the British Standards and BRE guidance indicate that OPC is suitable for use as in my previous posts.

I would be very interested to read publications which contradict BRE GPG18 regarding the use of OPC for RENDERING in buildings other than those of significant historic value. ie. those which are listed.

By the way, I have been using combined OPC and Lime mixes for more years than I care to remember. My experience tells me that the recomandations in BRE GPG18 work very well in practice.

Posted By: Mike George

Biff, rather a selective quotation that, perhaps you need to take Jon's advice as well<

Of course it's selective. I selected it from one of the ten papers I linked to for no better reason that, as I said, it caught my eye, and it seemed relevant particularly for folk who didn't want to wade through hours of reading.
As for taking Jon's advice, if I didn't have a hide thicker than the average mastodon, I'd have been insulted by such patronising nonsense. I have, of course, read every word of each of those papers over the last few years. Yes, I'm mostly interested in historic buildings, but that includes building new stuff in such a way that it stands a chance of becoming historic one day. Lime has stood the test of time and proved up to that job. And it doesn't result in so much CO2 pollution.

I just don't see why one should want to defend OPC. It's one of the many practices that makes the modern building industry such rubbish. What is it with you guys?

"OPC is a necessity", but you haven't said why, other than speed of build, and as I admitted, for strength in steel reinforced beams and suchlike, most of which we can probably do without.

" I'd have been insulted by such patronising nonsense."

It wasn't meant to be patronising Biff. Time is short for all of us. The subject discussed was carbon and the relative embodied carbon impacts. The numerous articles you have posted seem to be on the technical use of mortars.

As a leading proponent of lime on this forum it seems to me that it would be in your interest to read about this subject as this argument will impact adversely on the case for using lime: I had it cited to me yesterday in the Pub by a young engineer. He didn't, of course, realise that I wrote all the original technical arguments that were being quoted to him.

Repetition:

ADVANTAGES

•it imparts a chemical set which occurs before full shrinkage occurs, thereby reducing the risk of cracking

•layers may be built up more rapidly, without the need to wait a long time for one to set fully before applying the next

•it hardens rapidly, thereby providing protection from rain before carbonation has been completed. This helps to beat the inclement British weather

•being an artificial substance manufactured under closely controlled conditions, it is reliable and predictable in use

•it is available in a choice of colours, useful when it is necessary to match the colour of an existing mortar or render. ''

Wow, first you advocate a reference to justify your stance, quoting the bits you like. Then, when faced with the bits you don't like, you manage to spin them into something that you do. I bow to your masterfull interpretation.

I'm going to let someone else have a go now, [that is until something new is forthcoming] Also a final thought regarding the pole results so far. If they are like this on the Green Building Forum, imagine what they would be like on Wimpratt.com

Thank you. OPC is faster than lime. That's it.

Thanks Jon, Will have a look at that.

I think like many high CO2 emitting building materials OPC has its place, and where possible, and within budget constraints alternatives should be used if possible.

The post, post modern eco-age is going to be, I beleive one of a mix of new technologies and compromise unless there is enough pressure to pursuade governments to legislate against the vested interests of the giants of the construction materials manufacturing industry.

OPC however is one of the worst of all CO2 emitters, or as a colleague of mine states "with portland cement you get the double whammy on emissions, 1st from theenergy required to extract and process it and then from the CO2 relased by the clay in the manufacturing process". What sadens and worries me most is the deep conservtism of the building industry and the resistance to change I have encountered. OPC is the tip of a very large iceberg of ignorance, emissions in the construction industry does not stop at the materials and wastage but goes deep into the luxury lifestyles and SUV vehicle builders seem to favour as symbols of their commercial success.

Perhaps from this recession will emerg a better educated environmentally conscious and aware building industry ready to embrace rather than resist the new legislation that lies in wait for it in 2016.

LIME

The discussion, earlier in this thread, regarding the reabsorption of CO2 by lime and cement is RED HERRING and completely irrelevant - the CO2 emitted in the extraction processes, the heating and finally the transportation far exceeds any reabsortion.

Just select the 'text' option below the typing window

http://www.geopolymer.org/science/cements-concretes-toxic-wastes-global-warming