Lime FAQ's
This applies to stone and brick buildings. Not fascade/cavity built or impervious stone, they are slightly different and a lot rarer outside of civic and munincipal buildings in my area. Which is important because most craftwork is relevant to a specific area. as each have access to different materials. Obviously there are some things which are universal...
This applies to stone and brick buildings. Not fascade/cavity built or impervious stone, they are slightly different and a lot rarer outside of civic and munincipal buildings in my area. Which is important because most craftwork is relevant to a specific area. as each have access to different materials. Obviously there are some things which are universal...
These are my personal opinions. But far from uncommon within the craft industry or illogical. And to be taken humorously with no offence intended.
These are my personal opinions. But far from uncommon within the craft industry or illogical. And to be taken humorously with no offence intended.
Breathable: This is BULLSHIT. There is no legal definition that covers breathable within the construction industry and that claim could be made of most materials. It is very important.. My point being that a lot of products are sold as breathable but aren't in the application of Old Houses.
Breathable: This is BULLSHIT. There is no legal definition that covers breathable within the construction industry and that claim could be made of most materials. It is very important.. My point being that a lot of products are sold as breathable but aren't in the application of Old Houses.
Moisture passes through walls: this isn't true. It collects on the interior and exterior and then air flow causes it to evaporate through convection. That rate of convection is increased with the amount of lime present in the substrate. and air flow in and/or around the property. Stop closing chimneys donuts.
Moisture passes through walls: this isn't true. It collects on the interior and exterior and then air flow causes it to evaporate through convection. That rate of convection is increased with the amount of lime present in the substrate. and air flow in and/or around the property. Stop closing chimneys donuts.
Limecrete floors: almost no unbound air lime so not very "breathable." The cork edging is good. The insulation would be far better if it were solid and could cause problems as is. Usually installed in clay areas as replacement for suspended wooden floors originally specified to avoid clay heave or excessive groundwater. Yet no clay heave boards are ever installed with this and the cavities in the glass insulation could pose problems with excessive groundwater. This really bugs me as pretty much any other mix would be better. including a gauged Portland cement. mix. And it should be replaced with another timber floor. but everyone seems to love this system, presumably because groundworks and civils are like some form of arcane law or non-existent. to most people. This solution is good and works but still isn't as good as it could be. Its essentially a posh capillary break. The ground produces moisture as vapour and then the bottom or the slab and the foamed glass holds it until the humidity level in the ground drops. Kind of like a wall works but also not.
Limecrete floors: almost no unbound air lime so not very "breathable." The cork edging is good. The insulation would be far better if it were solid and could cause problems as is. Usually installed in clay areas as replacement for suspended wooden floors originally specified to avoid clay heave or excessive groundwater. Yet no clay heave boards are ever installed with this and the cavities in the glass insulation could pose problems with excessive groundwater. This really bugs me as pretty much any other mix would be better. including a gauged Portland cement. mix. And it should be replaced with another timber floor. but everyone seems to love this system, presumably because groundworks and civils are like some form of arcane law or non-existent. to most people. This solution is good and works but still isn't as good as it could be. Its essentially a posh capillary break. The ground produces moisture as vapour and then the bottom or the slab and the foamed glass holds it until the humidity level in the ground drops. Kind of like a wall works but also not.
French drains: when not offset from the wall or lined or with a discharge point it exasperates the problem. That's essentially an underground stream alongside the wall you want to dry out. Why do so many people think that's a good idea? Seriously some of these people are degree educated. Degree of stupidity if you ask me, no one ever does though. My preference is an offest french drain with a channel drain near the wall and paving like Yorkstone which allows the passage of vapour. This would collect all the run-off from the wall whilst reducing splashing on the wall base and preventing the ground from getting wet.
French drains: when not offset from the wall or lined or with a discharge point it exasperates the problem. That's essentially an underground stream alongside the wall you want to dry out. Why do so many people think that's a good idea? Seriously some of these people are degree educated. Degree of stupidity if you ask me, no one ever does though. My preference is an offest french drain with a channel drain near the wall and paving like Yorkstone which allows the passage of vapour. This would collect all the run-off from the wall whilst reducing splashing on the wall base and preventing the ground from getting wet.
NHL: most brands are not regulated for strength. Lean over rich is a hard no when trying to achieve breathability. Could cause cracking in brick and stone if used over large areas. Never inside. OK for very dense water impervious stone or with new construction in some scenarios. A certain brand of NHL 3,5 when tested showed as stronger than most OPC mortars and should have been called NHL 12. There is no scenario when you really need NHL's and you can do it all with hot mixes and pozzalons which have upper strength limits. St. Astier is regulated and good quality. Some of them are f##king atrocious. And they have sulphates in which cause effloressence. and damage masonry. I do use them in some scenarios and when I don't have a choice about the specification for whatever reason, be it a CO or Architect.
NHL: most brands are not regulated for strength. Lean over rich is a hard no when trying to achieve breathability. Could cause cracking in brick and stone if used over large areas. Never inside. OK for very dense water impervious stone or with new construction in some scenarios. A certain brand of NHL 3,5 when tested showed as stronger than most OPC mortars and should have been called NHL 12. There is no scenario when you really need NHL's and you can do it all with hot mixes and pozzalons which have upper strength limits. St. Astier is regulated and good quality. Some of them are f##king atrocious. And they have sulphates in which cause effloressence. and damage masonry. I do use them in some scenarios and when I don't have a choice about the specification for whatever reason, be it a CO or Architect.
Plastic Fibres: not dense enough mortars, Lime should be compacted to reduce shrinkage as the water leaves, This shouldn't be masked or prevented as it could lead to an increased number of larger pores. Hair works differently, more like reinforcing steel or fabric and generally still needs compacting a little and a mix with hair has to be a certain stiffness to hold the hair unlike fibred mixes which are usually very wet for ease of use. You don't beat back for the look, its to compact shrinkage. Plastic in traditional mortars.. WTAF? I would also point out that the most common application of fibres is in air lime mortars which are supposed to be weak and they increase compressive strength. Similar to pozzolans, these are a crutch for people who can't make very good mortar or who aren't very experienced with lime. Both can have negative effects on porosity.
Plastic Fibres: not dense enough mortars, Lime should be compacted to reduce shrinkage as the water leaves, This shouldn't be masked or prevented as it could lead to an increased number of larger pores. Hair works differently, more like reinforcing steel or fabric and generally still needs compacting a little and a mix with hair has to be a certain stiffness to hold the hair unlike fibred mixes which are usually very wet for ease of use. You don't beat back for the look, its to compact shrinkage. Plastic in traditional mortars.. WTAF? I would also point out that the most common application of fibres is in air lime mortars which are supposed to be weak and they increase compressive strength. Similar to pozzolans, these are a crutch for people who can't make very good mortar or who aren't very experienced with lime. Both can have negative effects on porosity.
Lime Putty: too wet and weak for external use beyond fine finishes, 5mm and under. Polished plaster and Ashlar pointing usually. Definitely not with fibres. This is lime which has been left in water to get as swollen as possible and shouldn't be confused with a traditional stiff paste with a minimum water content that should serve as the basis for most lime mortars. Use hydrated when you need pure as it was invented/developed for that reason.. I am not a fan of putty at all; it is mis-specified due to the word fine being mistaken for best. Its not, not even close and for a lot of applications its worse than other choices. Modern putty is always made by immersion too, which doesn't produce lime as good as a more controlled slaking with sprinkled water does. You then would produce the putty in a mill with water added gradually rather than all at once. the amount of water used to slake lime can vary from 0.5-1.5x.
Lime Putty: too wet and weak for external use beyond fine finishes, 5mm and under. Polished plaster and Ashlar pointing usually. Definitely not with fibres. This is lime which has been left in water to get as swollen as possible and shouldn't be confused with a traditional stiff paste with a minimum water content that should serve as the basis for most lime mortars. Use hydrated when you need pure as it was invented/developed for that reason.. I am not a fan of putty at all; it is mis-specified due to the word fine being mistaken for best. Its not, not even close and for a lot of applications its worse than other choices. Modern putty is always made by immersion too, which doesn't produce lime as good as a more controlled slaking with sprinkled water does. You then would produce the putty in a mill with water added gradually rather than all at once. the amount of water used to slake lime can vary from 0.5-1.5x.
Air lime for external use: generally too weak if used pure with washed concreting sands apart from limewash and not really historically accurate apart from a few exceptions. Historical aggregates usually imparted feeble hydraulicity. If that's even a word. It definitely should be. Hydraulication. Hydraulicizity. Hydraulicousness. ? Just to be crystal clear on this, I am not saying air lime mortars can't be used externally but rather the bullshit made from sloppy putty and washed sand sold by lime suppliers shouldn't be used externally... or ever if you value your sanity.
Air lime for external use: generally too weak if used pure with washed concreting sands apart from limewash and not really historically accurate apart from a few exceptions. Historical aggregates usually imparted feeble hydraulicity. If that's even a word. It definitely should be. Hydraulication. Hydraulicizity. Hydraulicousness. ? Just to be crystal clear on this, I am not saying air lime mortars can't be used externally but rather the bullshit made from sloppy putty and washed sand sold by lime suppliers shouldn't be used externally... or ever if you value your sanity.
Nationwide exposure ratings; there is a map of exposure levels throughout the country and these directly correlate with how much exterior masonry work there is on masonry properties eg. Scottish houses on the North West coast have thick roughcast lime render and limewash to protect them from the elements. In the South East of England the houses have exposed stone because Southerners live such soft lives. The irony being that the people up North do not follow these rules with their clothing because we're literally tougher than stone houses. I won't lie it tickled me for quite a while when that occurred to me. Especially as less than a week ago (February) I went out with two women and none of us wore a coat.. What the f##k is wrong with us? I work outside, one of them had two degrees and a Masters and the other own and runs a post natal exercise business....we definitely know better. On a more serious note; don't use things that hold water in places witha lot of water, like chalk aggregate in the NW. Chalk has an odd porosity too, it has narrow throats so the capillary action can be restricted. Also the reason not to use burnt chalk as a lime binder. And why shell lime is so brilliant. It has the perfect range of porosity.
Nationwide exposure ratings; there is a map of exposure levels throughout the country and these directly correlate with how much exterior masonry work there is on masonry properties eg. Scottish houses on the North West coast have thick roughcast lime render and limewash to protect them from the elements. In the South East of England the houses have exposed stone because Southerners live such soft lives. The irony being that the people up North do not follow these rules with their clothing because we're literally tougher than stone houses. I won't lie it tickled me for quite a while when that occurred to me. Especially as less than a week ago (February) I went out with two women and none of us wore a coat.. What the f##k is wrong with us? I work outside, one of them had two degrees and a Masters and the other own and runs a post natal exercise business....we definitely know better. On a more serious note; don't use things that hold water in places witha lot of water, like chalk aggregate in the NW. Chalk has an odd porosity too, it has narrow throats so the capillary action can be restricted. Also the reason not to use burnt chalk as a lime binder. And why shell lime is so brilliant. It has the perfect range of porosity.
Hempcrete: the opposite to how lime should be used. Not solid and soft with a lot of free lime but rather loose and hard with virtually none. I hate this stuff so much. It will crumble and settle over time if it doesn't get infested or rot. Is not even native, use Barley straw. which is cheaper, stronger and antibacterial. Or use a hemp plaster if you absolutely must. use hemp. Also pretty sure its just big pharma trying to get paid for their waste too. The only precedent for using hemp with lime is with fibres that look like cotton with internal plasters and or fermented as an organic additive to impart nano reinforcement, faster calcite formation etc.. Not bloody wood chip and shards of loosely compacted wood...it is so illogical and goes against the basic principles so much that it amazes me that I'm one of the only people who bemoans its extensive use.
Hempcrete: the opposite to how lime should be used. Not solid and soft with a lot of free lime but rather loose and hard with virtually none. I hate this stuff so much. It will crumble and settle over time if it doesn't get infested or rot. Is not even native, use Barley straw. which is cheaper, stronger and antibacterial. Or use a hemp plaster if you absolutely must. use hemp. Also pretty sure its just big pharma trying to get paid for their waste too. The only precedent for using hemp with lime is with fibres that look like cotton with internal plasters and or fermented as an organic additive to impart nano reinforcement, faster calcite formation etc.. Not bloody wood chip and shards of loosely compacted wood...it is so illogical and goes against the basic principles so much that it amazes me that I'm one of the only people who bemoans its extensive use.
Approved insulation boards on walls: a level of perfection is required during installation and maintenance that is unrealistic to achieve among other things. One crack equals a potentially ruined house. Ceilings and internal stud walls are good though, easier than lathwork but not cheaper. Lathwork is just shitwork that no-one wants to do. Good for introducing insulation between flooring joists.
Approved insulation boards on walls: a level of perfection is required during installation and maintenance that is unrealistic to achieve among other things. One crack equals a potentially ruined house. Ceilings and internal stud walls are good though, easier than lathwork but not cheaper. Lathwork is just shitwork that no-one wants to do. Good for introducing insulation between flooring joists.
Exposed Internal Masonry Walls: this is only possible in certain scenarios as it can lead to excessive cold bridging. Brick and stone construction have masonry units which pass through the wall from inside to out and if they aren't covered with an insulative layer of plaster and/or render then it will act as a thermal bridge which constantly draws heat out of the room. Besides which exposed brick and stone was very much last years trend. Its about as original as installing grey bifolds or buying a Tesla. The number of things I can do for feature walls and this is what people want. Please get out more. Read more books. Whatever it takes to not professionally bore me to death,.
Exposed Internal Masonry Walls: this is only possible in certain scenarios as it can lead to excessive cold bridging. Brick and stone construction have masonry units which pass through the wall from inside to out and if they aren't covered with an insulative layer of plaster and/or render then it will act as a thermal bridge which constantly draws heat out of the room. Besides which exposed brick and stone was very much last years trend. Its about as original as installing grey bifolds or buying a Tesla. The number of things I can do for feature walls and this is what people want. Please get out more. Read more books. Whatever it takes to not professionally bore me to death,.
Lower lime content over higher lime content(lean over rich) will equate to a damp wall from trapped moisture. Historic coal mortar has crumbled lime rich mortar behind it on a house I have worked on. so even back in the day they got it wrong. There is an external exception to this rule with impervious stone but that's another, much longer discussion.
Lower lime content over higher lime content(lean over rich) will equate to a damp wall from trapped moisture. Historic coal mortar has crumbled lime rich mortar behind it on a house I have worked on. so even back in the day they got it wrong. There is an external exception to this rule with impervious stone but that's another, much longer discussion.
One level higher.: in modern construction there is a very commonplace habit of over engineering everything by one position eg. one more scoop of cement in your mix which is fine because its rigid modern construction but with older properties its the other way around, it's best practice to err on the side of caution and use a mortar one weaker. Eg. don't use NHL5 to be better safe than sorry, its the wrong way around, And NHL3,5 is NOT 'medium' strength by any stretch of the imagination. Its called sacrificial mortar for a reason.
One level higher.: in modern construction there is a very commonplace habit of over engineering everything by one position eg. one more scoop of cement in your mix which is fine because its rigid modern construction but with older properties its the other way around, it's best practice to err on the side of caution and use a mortar one weaker. Eg. don't use NHL5 to be better safe than sorry, its the wrong way around, And NHL3,5 is NOT 'medium' strength by any stretch of the imagination. Its called sacrificial mortar for a reason.
Hydrated Lime: steam slaked pure lime. Stronger then putty when used correctly. Specifically developed for low skilled mixing on site during the Victorian period. The irony that all the people who it was designed for saying its unsuitable for use is far from lost on me. It's essentially NHL 1. And its generally old when bought from a builders merchants, that's why it performs poorly. There is a guy on youtube who has an old video of this and he is my sort of guy, no f##ks given, just does the job with lime. Legend. I also know a plasterer who is rather prolific in the SE who only uses hydrated lime when he has the option now.
Hydrated Lime: steam slaked pure lime. Stronger then putty when used correctly. Specifically developed for low skilled mixing on site during the Victorian period. The irony that all the people who it was designed for saying its unsuitable for use is far from lost on me. It's essentially NHL 1. And its generally old when bought from a builders merchants, that's why it performs poorly. There is a guy on youtube who has an old video of this and he is my sort of guy, no f##ks given, just does the job with lime. Legend. I also know a plasterer who is rather prolific in the SE who only uses hydrated lime when he has the option now.
"Hot Lime": over used designation and incorrectly applied to pretty much any premixed mortar. The most benefit from hot lime comes from using it hot and freshly mixed so ANY hot mix sold is not as good as making it yourself. It should be sold as clearly as cold, hot mix. People struggle with using hot lime mixes and pure limes in general and do a number of ill advised things, the most common is the use of pozzalons in your hot mix to create a hydraulic set. Fine, but the pozzalon people prefer is metakaolin which is dangerously powerful and when you combine aluminium silicates with magnesium the strength continues to increase exponentially. Magnesium can be found in an awful lot of places such as impure limes and aggregates. And one of the limes sold in the UK has it in. Hot lime mortars can also easily be TOO porous but this is very hard to gauge without experience. So much confusion in this area due to certain properties being contrary to one another or present in multiple limes and the confusion over how they work. Another argument for why on Earth did we forget/ignore all that trial and error testing the Ancients did over thousands of years?
"Hot Lime": over used designation and incorrectly applied to pretty much any premixed mortar. The most benefit from hot lime comes from using it hot and freshly mixed so ANY hot mix sold is not as good as making it yourself. It should be sold as clearly as cold, hot mix. People struggle with using hot lime mixes and pure limes in general and do a number of ill advised things, the most common is the use of pozzalons in your hot mix to create a hydraulic set. Fine, but the pozzalon people prefer is metakaolin which is dangerously powerful and when you combine aluminium silicates with magnesium the strength continues to increase exponentially. Magnesium can be found in an awful lot of places such as impure limes and aggregates. And one of the limes sold in the UK has it in. Hot lime mortars can also easily be TOO porous but this is very hard to gauge without experience. So much confusion in this area due to certain properties being contrary to one another or present in multiple limes and the confusion over how they work. Another argument for why on Earth did we forget/ignore all that trial and error testing the Ancients did over thousands of years?
No cement ever!; this is also inaccurate. There are applications when its perfectly acceptable as with any binder. Even on old houses. This is normally the rally cry of the s called lime expert or specialist. But I would say that you cannot in any circumstances use mass produced standard OPC, it has to be of a better quality and really I'd suggest that natural/Roman is a better choice or even hourdex for the majority of applications.
No cement ever!; this is also inaccurate. There are applications when its perfectly acceptable as with any binder. Even on old houses. This is normally the rally cry of the s called lime expert or specialist. But I would say that you cannot in any circumstances use mass produced standard OPC, it has to be of a better quality and really I'd suggest that natural/Roman is a better choice or even hourdex for the majority of applications.
Thermal dilation AKA expansion and contraction; lime expands by twice that of most bricks and stone however the strength is so low the bricks and stone contain it. Cement AKA OPC can't be contained so cause issues such as delamination from the bricks and stone, shear cracking. Lime also aurogenously heals, cement just cracks.
No gypsum ever!: again this is inaccurate and in some scenarios its perfectly fine eg. a hot house with lots of air flow. A lot of Victorian brick built town houses have it. But theere is a current trend of using wood ash with lime, this will produce a water soluble form of gypsum that can be washed out so not cool externally.
No gypsum ever!: again this is inaccurate and in some scenarios its perfectly fine eg. a hot house with lots of air flow. A lot of Victorian brick built town houses have it. But theere is a current trend of using wood ash with lime, this will produce a water soluble form of gypsum that can be washed out so not cool externally.
Only lime, replace it all!: this is rarely necessary but because of a number of the points listed its far easier to do than a bespoke application that takes into account existing materials which can be utilised or repaired. Eg. if you stick one lime next to another and its doesn't match one of them will be bone dry and the other will be soaking wet. And again Lean over rich.
Only lime, replace it all!: this is rarely necessary but because of a number of the points listed its far easier to do than a bespoke application that takes into account existing materials which can be utilised or repaired. Eg. if you stick one lime next to another and its doesn't match one of them will be bone dry and the other will be soaking wet. And again Lean over rich.
It's grey so it's cement; not in the least bit accurate. There are entire areas where the predominate sand is silver sand which produces grey mortars. Heswall I'm looking at you, I laughed in a clients neighbours face over this. He'd spent an awful lot of time carefully removing very, very good quality lime render because it was grey, I pointed at the obvious lime inclusions and asked him what they were. It had been applied hot so had quite few and they were large. It was grey because the house was built on a beach of silver sand, clues in the name! He was heartbroken.
It's grey so it's cement; not in the least bit accurate. There are entire areas where the predominate sand is silver sand which produces grey mortars. Heswall I'm looking at you, I laughed in a clients neighbours face over this. He'd spent an awful lot of time carefully removing very, very good quality lime render because it was grey, I pointed at the obvious lime inclusions and asked him what they were. It had been applied hot so had quite few and they were large. It was grey because the house was built on a beach of silver sand, clues in the name! He was heartbroken.
Salts: my nemesis1 These are mineral salts which are present in a lot of different things eg. chimneys breast, clay heavy soils, Portland cement, aggregates, natural water, bricks etc. They are soluble and travel through water getting deposited when it evaporates. These salts expand and damage stone. They can also chemically react with active substances like lime creating new minerals which can also be harmful to masonry. The salts are often hygroscopic in nature too. F##king salt, its the best and worst thing for masonry, when you quarry stone the salt mineral water it sits in evaporates creating a hardened crust on the surface of the stone helping it resist erosion but that same effect can be present in lime mortars that are saturated with impurities for a wide variety of reasons.
Salts: my nemesis1 These are mineral salts which are present in a lot of different things eg. chimneys breast, clay heavy soils, Portland cement, aggregates, natural water, bricks etc. They are soluble and travel through water getting deposited when it evaporates. These salts expand and damage stone. They can also chemically react with active substances like lime creating new minerals which can also be harmful to masonry. The salts are often hygroscopic in nature too. F##king salt, its the best and worst thing for masonry, when you quarry stone the salt mineral water it sits in evaporates creating a hardened crust on the surface of the stone helping it resist erosion but that same effect can be present in lime mortars that are saturated with impurities for a wide variety of reasons.
Same day mixes; it is very rare unless using hot mixed mortars, hot to use a mortar on the same day it's prepared and even then my preference would be to add a little old mortar in to reduce shrinkage and for increased workability. The efforts you have to go to with preparing your aggrgates is a little irritating to say the least. Yes there are people who mix and use the same day, but I can almost guarantee they have to do a lot of aftercare or compromise their mortar to do so, pozzalons, fibres etc.
Same day mixes; it is very rare unless using hot mixed mortars, hot to use a mortar on the same day it's prepared and even then my preference would be to add a little old mortar in to reduce shrinkage and for increased workability. The efforts you have to go to with preparing your aggrgates is a little irritating to say the least. Yes there are people who mix and use the same day, but I can almost guarantee they have to do a lot of aftercare or compromise their mortar to do so, pozzalons, fibres etc.
3:1 sharp sand:lime mortars; this is usually too porous and can often let in more water than it can convect off. Another non word. These sands are graded for use with OPC not lime. A lime supplier will have good quality mortar sands but they are expensive. Or just ask the mason who works for you where to get it locally.
3:1 sharp sand:lime mortars; this is usually too porous and can often let in more water than it can convect off. Another non word. These sands are graded for use with OPC not lime. A lime supplier will have good quality mortar sands but they are expensive. Or just ask the mason who works for you where to get it locally.
Eco/green building crossover: a lot of products being sold to the traditional/heritage market are actually designed and proven on new build applications and very clearly listed as not suitable or requiring testing prior to use but this is often overlooked. The Guardian reading hemp botherers who firmly believe that a sign of good craftsmanship is when something looks a bit shit absolutely love this crap. "Lets import and produce a load of stuff in factories and just believe the spiel like its gospel, woohoo we're saving the World!".
Branded Lime Products: very, very few of these are suitable for traditional use or even proven over a long enough period. They often have additives which aren't listed and include unregulated NHL's. But the old school ones are the nuts. Vicat, Hourdex etc. I'm sure some of new FL's will prove to be effective but IMO its too soon to tell. The most popular insulative plaster on the market is absolutely terrible, it ignores the fundamentals of how lime works and what one is trying to achieve.
3,2,1 traditional plastering; the significance of this cannot be understated, The reason behind layering the plaster with progressively more lime towards the surface is because the amount of lime has a direct effect upon the rate of capillarity so if this is reversed it can draw water backwards into the wall holding it there indefinitely and causing damp. Lean over rich again! And again there are exceptions to this rule with some external applications but you can get f##ked if you think I'm saying what or when in a time when an off duty doctor will let someone die rather than get sued and with good reason.