Lime ceiling follow up

Members online

No members online now.
#1
Hi guys, again im after advice following the intsallation of a new lath ceiling, i applied a hair first coat using cooled down hotmix (plenty of hair) and left to dry for a month, i put alot of water on it and the n applied nhl lime 2nd coat, with hair and left for 4 days and put a 4mm lime putty top coat on, hardly any water in the mix.this was done 2 weeks ago and today i have noticed cracking! Ive managed to rub them back but why all of a sudden have they appeared?? Do i continuously need to be spraying lightly? What am i missing?? Any help woukd be great as im doing my whole house and dint want this to be a continued problem
 
#4
But its 2 coats up, 1st coat was a hot mix, 2nd was nhl and finish cost was putty and silica sand
 
#7
I never mix a putty coat over a NHL.
Go for a pre bagged mix, I am based in Hertfordshire it is almost impossible to find a decent local sand, the minute you start mixing them with grain particle sizes is where the problems can start to happen, your local travis will only stock plastering/building/ screed, Dependent on where you live leave the science bit to one of the big lime companies
 
#8
I believe my house to be built in hotmix, i cant see how the country was built solely on putty or nhl, logistic's cant work! its an old farmers house, all no frills.
The nhl coat was that insulated Ultra, cant think of the brand name? Its lightweight when mixed so i thought it it may relieve pressures on the laths, but thinking properly i can see why you should use one type of lime, curing in different ways would push and pull at it?
 
#9
I never mix a putty coat over a NHL.
Go for a pre bagged mix, I am based in Hertfordshire it is almost impossible to find a decent local sand, the minute you start mixing them with grain particle sizes is where the problems can start to happen, your local travis will only stock plastering/building/ screed, Dependent on where you live leave the science bit to one of the big lime companies
Whats the issue with merchant sands??
 

vfr12

Well-Known Member
#10
I believe my house to be built in hotmix, i cant see how the country was built solely on putty or nhl, logistic's cant work! its an old farmers house, all no frills.
The nhl coat was that insulated Ultra, cant think of the brand name? Its lightweight when mixed so i thought it it may relieve pressures on the laths, but thinking properly i can see why you should use one type of lime, curing in different ways would push and pull at it?
I was about to teach you history, but I see you know about it .
Hot lime was used in the 18th century simply to match the explosive demand for the growing metropolis,where slaked lime was thrown trough screens to remove unslaked lime.its a simple process, less labour intensive and time consuming,which had to be back then. Hot lime will be the last thing I'll be using today for render and plaster. Mature lime putty is way better and will give you better results and finish.
Saying that, hot lime has also its advantages. In some circumstances hot mortar is advantageous-building with hard , impermeable stones, especially in cold, damp conditions,very little water is absorbed by the masonry, so building can be slow do to the risk of slumping.Hot mortars encourage evaporation and initial stiffening of the mortar.The heat is believed to improve the bond between sand and lime and may also activate some pozolanic content in the sand.Hot lime was common for foundation and core filling, but also for cold weather works.The ratio is 1:2;1:1.
I would suggest you take down the existing plaster and replace it with lime putty, or if you fancy hemp lime. The hot lime has cracked like spider net and is not reliable. To make things worse- you have used two different times of limes over each other! You can't make this up!
 
#12
Il learn to live with cracks now, i simply cant take it down, ive the whole house to do and this was the smallest, least used room, a practice and experiment room, il take what ive learned from this room and not make the same mistakes again i hope! I do like the idea of using hotmix, what disadvantages do hotmixing render have over putty? Can i 3 coat in it with a putty finish coat? Does it just need to to have a misting every morning and night? From what ive read, the sand in hotmix doesnt need to be as 'clean', as mortar its been bang on, ive built a wall in it with no issues, and i plan on re building a whole shed with it with some brick dust as a pozzolan over the winter(im in no real rush)
 

JessThePlasterer

Well-Known Member
#13
I was about to teach you history, but I see you know about it .
Hot lime was used in the 18th century simply to match the explosive demand for the growing metropolis,where slaked lime was thrown trough screens to remove unslaked lime.its a simple process, less labour intensive and time consuming,which had to be back then. Hot lime will be the last thing I'll be using today for render and plaster. Mature lime putty is way better and will give you better results and finish.
Saying that, hot lime has also its advantages. In some circumstances hot mortar is advantageous-building with hard , impermeable stones, especially in cold, damp conditions,very little water is absorbed by the masonry, so building can be slow do to the risk of slumping.Hot mortars encourage evaporation and initial stiffening of the mortar.The heat is believed to improve the bond between sand and lime and may also activate some pozolanic content in the sand.Hot lime was common for foundation and core filling, but also for cold weather works.The ratio is 1:2;1:1.
I would suggest you take down the existing plaster and replace it with lime putty, or if you fancy hemp lime. The hot lime has cracked like spider net and is not reliable. To make things worse- you have used two different times of limes over each other! You can't make this up!
Ok, you’ve just earned a place on my dinner party list! :sisi:
 

Dropsalot

Private Member
#14
Oh Christ lads it’s only been three minutes since the wedding and now she wants “dinner parties”..........keyrings in a bowl I’ll wager......



Hussy!
 

vfr12

Well-Known Member
#17
Il learn to live with cracks now, i simply cant take it down, ive the whole house to do and this was the smallest, least used room, a practice and experiment room, il take what ive learned from this room and not make the same mistakes again i hope! I do like the idea of using hotmix, what disadvantages do hotmixing render have over putty? Can i 3 coat in it with a putty finish coat? Does it just need to to have a misting every morning and night? From what ive read, the sand in hotmix doesnt need to be as 'clean', as mortar its been bang on, ive built a wall in it with no issues, and i plan on re building a whole shed with it with some brick dust as a pozzolan over the winter(im in no real rush)
Sure, no problem if it’s your house !These cracks will turn into small separate sections, you know that right? There is a huuuuuuuuge difference between hot - putty - nhl ! I don’t think you’ll change your choice nor work direction , so I will spare you the lecture. What’s your ratio for hot lime btw ?
 
#18
I kind of do know my coarse, im really not bothered about the amount of blood and sweat going into my house as long as im not harming it, i have 9" walls and ive read the arguments that a slaked lime(putty/hm) offers a better vapour permiability than a nhl. Hot mix is a 3:1, 2grit,1 red(for colour) so when mixed it will be rich, i think thats why i like the idea of it, plenty of lime in there, especially for cost effectiveness. I Do know the differences between nhl and putty in practice and the science of them both but im new to actually using it, so im all for being educated as long as folk are prepared for questions? So lecture away, the only thing i really want is to be true to my house the best i can,
 

vfr12

Well-Known Member
#19
I honestly can say whatever you think you know, it’s not near good enough for your house. Anyway, carry on and all the best! I haven’t mentioned it before, but the only time I have used hot lime recently was for waterproof lime wash . This might be useful after all. (y)
 
#20
Far to many factors can go wrong with this. Is your 3-1 ratio weighed or gauged by buckets? Would you say your red sand is building sand? If so depending where you are down my way that's far to dirty to use and the sharp is to gritty. I would say the is just as much skill in finding the right material and mixing it to spreading it on the wall
 

Tinytom

Well-Known Member
#23
I honestly can say whatever you think you know, it’s not near good enough for your house. Anyway, carry on and all the best! I haven’t mentioned it before, but the only time I have used hot lime recently was for waterproof lime wash . This might be useful after all. (y)
The man knows his apples.
I did some lime work earlier in the summer, I put horse hair in the backing coat and it was awful to work with. Didn’t enjoy it at all
 
#24
I was about to teach you history, but I see you know about it .
Hot lime was used in the 18th century simply to match the explosive demand for the growing metropolis,where slaked lime was thrown trough screens to remove unslaked lime.its a simple process, less labour intensive and time consuming,which had to be back then. Hot lime will be the last thing I'll be using today for render and plaster. Mature lime putty is way better and will give you better results and finish.
Saying that, hot lime has also its advantages. In some circumstances hot mortar is advantageous-building with hard , impermeable stones, especially in cold, damp conditions,very little water is absorbed by the masonry, so building can be slow do to the risk of slumping.Hot mortars encourage evaporation and initial stiffening of the mortar.The heat is believed to improve the bond between sand and lime and may also activate some pozolanic content in the sand.Hot lime was common for foundation and core filling, but also for cold weather works.The ratio is 1:2;1:1.
I would suggest you take down the existing plaster and replace it with lime putty, or if you fancy hemp lime. The hot lime has cracked like spider net and is not reliable. To make things worse- you have used two different times of limes over each other! You can't make this up!
Does the nhl lime go harder over time more than the hot lime? Maybe not the hot lime the problem here?
 

vfr12

Well-Known Member
#25
Does the nhl lime go harder over time more than the hot lime? Maybe not the hot lime the problem here?
Of course. NHL is the “hardest “ lime. The stone that comes from is way harder And heavier than the one lime putty comes from. The compressive strength is achieved in long term. Test are usually made after 28 days or more. Lime putty with pozzolans can reach 6-7 MPa in 5 years. NHL2 for instance can reach The same strength much quicker because is hydraulic lime. NHL3,5 and 5 can reach the same strength in 28 days and double it in 5 years. As you can see lime set is very slow and develops over the years. Hot lime on the other hand does not fall in this category. It’s the beginning stage of lime putty and failure Is written all over it.
And the problem in this particular case is the op has used two different types of lime over each other.
 
Last edited:
#26
Of course. NHL is the “hardest “ lime. The stone that comes from is way harder And heavier than the one lime putty comes from. The compressive strength is achieved in long term. Test are usually made after 28 days or more. Lime putty with pozzolans can reach 6-7 MPa in 5 years. NHL2 for instance can reach The same strength much quicker because is hydraulic lime. NHL3,5 and 5 can reach the same strength in 28 days and double it in 5 years. As you can see lime set is very slow and develops over the years. Hot lime on the other hand does not fall in this category. It’s the beginning stage of lime putty and failure Is written all over it.
And the problem in this particular case is the op has used two different types of lime over each other.
Thanks for your reply pozzolans are they just for protection from frost ? Therefore not needed indoors?
 

vfr12

Well-Known Member
#32
Pozzolans indeed are speeding things, but not in the way you are imagining it. They are used mainly with air lime due to the time it takes to set and cure. This type of lime is very vulnerable in the first hours and days after. Great care should be taken to get it right and pozzolans alone will not guarantee success no matter what. What pozzolans do is giving you the start you need. Mixed with water they don’t react, but mixed with lime - big time. How reactive pozzolana is depends on the grain size- the smaller the biger surface for reaction. They need to be used with great care because they change the lime structure and reduce permeability and flexibility. Every bagged render on the market contains silica and alumina. I have started a test yearly this year to see if I am right to think today’s render does not come close to the traditional lime plaster. The first test wasn’t conducted 28 days and the second 6 months after. Favourite so far is the mix with vulcanic ash and second is with argical

E3766214-60CF-4675-B78A-399429E7C09F.jpeg
4892E205-3746-42C9-B25C-5D277749D802.jpeg