- Thread starter Craig
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In concurring with NT I offer the following extract taken from an artical written by Ian Pritchett in 1997
The whole of this paper can be found at the following link
http://www.ihbc.org.uk/context_archive/54/overviewlimes.htm
The whole of this paper can be found at the following link
http://www.ihbc.org.uk/context_archive/54/overviewlimes.htm
Thats interesting - thank you. I am just about to read the article.
I checked out my old building technology books from the 1870s and they dismiss lime stucco as being outdated and recommend a straight portland cement mix for all work (though they note that it can be expensive as men tend to work it too long!).
The estates gazette's repair of houses book suggests a mix of 1:2:6 as well, giving that it will give a stronger bond whilst remaining porous.
It seems that the original use of stucco/render pre-cement was very problematic and in an attempt to create a more durable finish, our favourite substance, burnt linseed oil was even used as an additive?
I checked out my old building technology books from the 1870s and they dismiss lime stucco as being outdated and recommend a straight portland cement mix for all work (though they note that it can be expensive as men tend to work it too long!).
The estates gazette's repair of houses book suggests a mix of 1:2:6 as well, giving that it will give a stronger bond whilst remaining porous.
It seems that the original use of stucco/render pre-cement was very problematic and in an attempt to create a more durable finish, our favourite substance, burnt linseed oil was even used as an additive?
So if I understand those articles (which appear to have an argument with each other), if I specify a hydraulic lime (which is the stuff that appears in a powdered form in a bag and is mixed on site) then this will provide a hard-ish/porous-ish render?
And the author is saying that the habit of gauging in cement is due to not being able to get hydraulic limes in the past?
And the author is saying that the habit of gauging in cement is due to not being able to get hydraulic limes in the past?
Lynn
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I think the point is to match the new material used to the original. If it had cement in the past, then you can use it. If not then the cement mix will be too hard and make the substrate fail over time.
Interesting article.
Interesting article.
The house predates portland cement's invention, though this may not be the original render - or at least the top layer - its pretty thick. They had rendered over the lead drain pipes set into the wall, which suggest many coats overtime?
Anyway, all the old render is falling off, as it has blown. I spoke to Womersleys and also spoke to the contractors - they are both suggesting a medium to strong naturally hydraulic lime, so thats what we are going with.
Here is the pavment vault we unearthed:
http://putfile.com/pic.php?pic=main/8/22106472085.jpg&s=f10
Here is the wall at the rear:
http://putfile.com/pic.php?pic=main/8/22106454939.jpg&s=f10
Anyway, all the old render is falling off, as it has blown. I spoke to Womersleys and also spoke to the contractors - they are both suggesting a medium to strong naturally hydraulic lime, so thats what we are going with.
Here is the pavment vault we unearthed:
http://putfile.com/pic.php?pic=main/8/22106472085.jpg&s=f10
Here is the wall at the rear:
http://putfile.com/pic.php?pic=main/8/22106454939.jpg&s=f10
Nemesis
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The lime purchased in bags in powder form is hydrated lime not hydraulic. Hydraulic should be used with caution, and only for certain situations. Non-hydraulic lime is usually the most appropriate material to use.
In 1870, Portland Cement was still a relatively new wonder material. Naturally lime stucco was considered old fashioned. Consider, too, that there were many varieties of stucco, developed over time, some more effective and reliable than others.
Modern methods of lime manufacture make it rather a more consistent product than in previous centuries.
A decent lime mortar mix should not require cement to be added, and the Smeaton Project did indeed demonstrate that over time the addition of modern cement to a lime mortar could lead to premature failure.
In 1870, Portland Cement was still a relatively new wonder material. Naturally lime stucco was considered old fashioned. Consider, too, that there were many varieties of stucco, developed over time, some more effective and reliable than others.
Modern methods of lime manufacture make it rather a more consistent product than in previous centuries.
A decent lime mortar mix should not require cement to be added, and the Smeaton Project did indeed demonstrate that over time the addition of modern cement to a lime mortar could lead to premature failure.
Yes, I read some other articles this morning and they highlight the problem of salts in the wall attacking the cement and the risk of disaggregation in low ratio mixes.
The wall retains earth and is thus continuously damp. What I read suggested that a non-hydraulic lime may not go off properly in these situations.
Mike Wye's site recommends using a non-hydraulic lime but then mixing in a pozzalan to achieve a hydraulic behaviour.
That whole hydrated/hydraulic thing is frankly very confusing!
The wall retains earth and is thus continuously damp. What I read suggested that a non-hydraulic lime may not go off properly in these situations.
Mike Wye's site recommends using a non-hydraulic lime but then mixing in a pozzalan to achieve a hydraulic behaviour.
That whole hydrated/hydraulic thing is frankly very confusing!
I'm reading a lot of confusion here. The comment from the 1870s sounds like the sort of flippant remarks many make their decisions on rather than anything to do with fact or logic.
1800s cements were much weaker than todays OPC, and it is not a good idea to replace historic cement render with new cement render, as the usual problems will then occur.
I'll let someone else answer the hydraulic question, as I'm liable to suggest pasta for that
NT
1800s cements were much weaker than todays OPC, and it is not a good idea to replace historic cement render with new cement render, as the usual problems will then occur.
I'll let someone else answer the hydraulic question, as I'm liable to suggest pasta for that
NT
I have a number of books from various periods and the fascination with Portland cement is an enduring one.
One of the most interesting is from a supposed bible of conservation - The Care and Conservation of Georgian Houses, vaguely mentions that lime has become fashionable recently and that there may be some advantages to using it which people might want to look into.
Then they recommend taking out the wooden lintels in the cellar to replace them with reinforced concrete and then layering waterproof cement onto chicken wire...
Anyway - I don’t have a cementious render currently (probably) and as a result of your advice, aint about to have one - I would be very pleased to hear advice on the hydraulic/non-hydraulic though?
One of the most interesting is from a supposed bible of conservation - The Care and Conservation of Georgian Houses, vaguely mentions that lime has become fashionable recently and that there may be some advantages to using it which people might want to look into.
Then they recommend taking out the wooden lintels in the cellar to replace them with reinforced concrete and then layering waterproof cement onto chicken wire...
Anyway - I don’t have a cementious render currently (probably) and as a result of your advice, aint about to have one - I would be very pleased to hear advice on the hydraulic/non-hydraulic though?
Nemesis
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If the wall is permanently damp, consider a weakly hydraulic as it relies on a chemical set. In this situation non-hydraulic may not carbonate. A non-hydraulic with a pozzolan is a possible alternative, and in that case bagged lime with a pozzolan is a very inexpensive way of achieving this.
Before carrying out anything, I would suggest a discussion with Mike Wye, ask what he suggests, or another of the many lime suppliers. SPAB I would also discuss this with.
As the wall is under pressure from the earth behind, consider adding small weep holes to relieve the pressure and allow some water to escape.
Avoid anything which is not going to be easily removed in future without damage to the wall.
Another option is to leave the wall unrendered and simply point; however, presumably you wish to maximise the light and paint the wall white.
Before carrying out anything, I would suggest a discussion with Mike Wye, ask what he suggests, or another of the many lime suppliers. SPAB I would also discuss this with.
As the wall is under pressure from the earth behind, consider adding small weep holes to relieve the pressure and allow some water to escape.
Avoid anything which is not going to be easily removed in future without damage to the wall.
Another option is to leave the wall unrendered and simply point; however, presumably you wish to maximise the light and paint the wall white.
Yes, maximising the light is a big factor. I did speak with Womersley, and their recommendation for a damp wall was NHL5, which is their strongest hydraulic lime - the contractor felt a less strong lime would be better. Agree on the weep holes. In the photo I posted, you cant really see the lovely big lead ones set in the wall.
Gervase
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I'd got with an NHL3.5 for render. Fat lime can be used, but unless you're going to give it at least five coats of limewash immediately and then repaint annually you'll find the fat lime render won't be as durable, particularly if the wall is to windward and catches the rain.
Hydraulic render would only be an issue if structural movement is likely - if you've recently had some windows enlarged, new lintels, doors widening and the like, then the stresses on the building as a whole will have changed and you should expect some movement to accommodate this. In which case fat lime is far better at 'healing' itself than hydraulic lime.
Hydraulic render would only be an issue if structural movement is likely - if you've recently had some windows enlarged, new lintels, doors widening and the like, then the stresses on the building as a whole will have changed and you should expect some movement to accommodate this. In which case fat lime is far better at 'healing' itself than hydraulic lime.
Nemesis wrote:
Both Hydrated and Hydraulic limes come in bagged powder form. Though Hydrated lime is the one generally found at your local builders merchants.
It can be mixed with water to form lime putty or used staight from the bag.
Natural Hydraulic lime (NHL) when mixed with water will set within a few hours. The number after NHL (eg NHL5, NHL3.5, NHL2) relates to the amount of natually occuring impurities within the limestone prior to manufacture and so during the manufacture these impurities get burt and then act as a pozzolan ready mixed within the lime, with 5 being the most impure and strongest and 2 being the least impure and weakest (The "Strength" or Weakness" refers to the set and is not an indication of quality or of one being better than the other, it's just different qualities for different applications). They are also refered to as Eminently (5), Moderately (3.5) and Feebly (2) hydraulic and although not so readily available they are fairly easy to get hold of.
Also with regards to any books or journals relating to cement and lime in building it is worth considering when they were written and the thinking of the time. In 1870 cement was a reletively new innovation in building and though it was generally used for facades as a cheap immetation of portland stone, as the manufacture improved and the price fell it soon became the material of choice as it enabled year round constuction and faster builds. Unfortunately as with so many "Wonder Products" it's legacy has long lasting consequencies. That is not to say cement has no place in construction only that it's place in conservation is very limited
Both Hydrated and Hydraulic limes come in bagged powder form. Though Hydrated lime is the one generally found at your local builders merchants.
It can be mixed with water to form lime putty or used staight from the bag.
Natural Hydraulic lime (NHL) when mixed with water will set within a few hours. The number after NHL (eg NHL5, NHL3.5, NHL2) relates to the amount of natually occuring impurities within the limestone prior to manufacture and so during the manufacture these impurities get burt and then act as a pozzolan ready mixed within the lime, with 5 being the most impure and strongest and 2 being the least impure and weakest (The "Strength" or Weakness" refers to the set and is not an indication of quality or of one being better than the other, it's just different qualities for different applications). They are also refered to as Eminently (5), Moderately (3.5) and Feebly (2) hydraulic and although not so readily available they are fairly easy to get hold of.
Also with regards to any books or journals relating to cement and lime in building it is worth considering when they were written and the thinking of the time. In 1870 cement was a reletively new innovation in building and though it was generally used for facades as a cheap immetation of portland stone, as the manufacture improved and the price fell it soon became the material of choice as it enabled year round constuction and faster builds. Unfortunately as with so many "Wonder Products" it's legacy has long lasting consequencies. That is not to say cement has no place in construction only that it's place in conservation is very limited
Nemesis
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The lime most readily found in bags at builders' merchants is hydrated lime. To ensure it is fresh and hasn't already carbonated in the bag the bag should be plastic lined. Problems used to occur before bags were lined, and it was not recommended for use in lime mortars and renders because of this problem.
http://www.rose-of-jericho.demon.co.uk/main/spab1999.htm
makes interesting reading.
Early uses of Portland Cement, which was introduced in the mid-19th century, also included house construction. A number of these survive.
http://www.rose-of-jericho.demon.co.uk/main/spab1999.htm
makes interesting reading.
Early uses of Portland Cement, which was introduced in the mid-19th century, also included house construction. A number of these survive.
Gervase
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Jewson's will supply Castle hydraulic limes in bags either loose or palleted. As, indeed, will most builder's merchants. If you have a trade account it works out a lot cheaper than most lime specialists (sadly).