Rendering an old house
Discussion
Old farm house, approx 200 years old solid walls 1-2' thick, mixture of stone, flint, chalk and brick.
Previous farmers rendered with a cement based render many years ago, variously blown, cracked etc. causing damp.
Obviously old render needs to come off, question is what next?
Lime render sounds like a PITA, costly, maintenance etc. Internally is largely modern plaster, we did lime render one wall about 5 years ago and it has almost dried out! We have internally insulated one aspect upstairs, allowing recommended air gaps etc.
Is there another option ? was thinking a more modern render and then external insulation, particularly the end gable as it bears the brunt of the weather. We replaced the roof a couple of years ago and increased the overhang to allow potential external insulation in future... the damp is largely mid wall, not close to the ground.
Hoping to get this done in the summer, so need to get talking to trades, and would prefer to not go in completely blind.
Thanks for your input
Previous farmers rendered with a cement based render many years ago, variously blown, cracked etc. causing damp.
Obviously old render needs to come off, question is what next?
Lime render sounds like a PITA, costly, maintenance etc. Internally is largely modern plaster, we did lime render one wall about 5 years ago and it has almost dried out! We have internally insulated one aspect upstairs, allowing recommended air gaps etc.
Is there another option ? was thinking a more modern render and then external insulation, particularly the end gable as it bears the brunt of the weather. We replaced the roof a couple of years ago and increased the overhang to allow potential external insulation in future... the damp is largely mid wall, not close to the ground.
Hoping to get this done in the summer, so need to get talking to trades, and would prefer to not go in completely blind.
Thanks for your input
The centre section of our house is circa 120 years old and part rendered and when we bought it the surveyor was good at explaining these old buildings were not designed to be heavily insulated and rendered so my advice would be get somebody in who knows what they are talking about to survey what you have and recommend a solution.
I would use a NHL render (probably a 3) - this will allow moisture/vapour pressure from inside to pass through through the structure avoiding a build up of moisture in the outer zone of the walls, as will almost certainly be found when the cement render is removed - a wet wall has much lower resistance to the passage of heat. A nylon mesh in the base coat will deal with any variability in the walling material and control cracking.
Putty lime would be better still but it is a PITA to manage while it takes a set, so NHL provides a pragmatic solution with similar characteristics to an 'air' lime if not in terms of ultimate vapour permeability.
Putty lime would be better still but it is a PITA to manage while it takes a set, so NHL provides a pragmatic solution with similar characteristics to an 'air' lime if not in terms of ultimate vapour permeability.
Thanks for the replies.
Not listed (wouldn't buy a listed property again!)
No wooden lintels left, previous farmers rather ingeniously managed to pour reinforced concrete lintels in situ. I know as we removed a load bearing wall and had to use a world of steel, and replace the nearest lintel with an RSJ as the engineer wasn't happy with the overlap.
Yes, cladding is kind of what I was getting at, but although not listed, it is in a conservation area, so easier if it doesn't materially alter the aesthetics.
I'll certainly get an old buildings guy in, but I imagine he will suggest lime, which is perhaps the way to go.
I appreciate that cement based render is completely wrong for the building, as it is impermeable, inflexible etc.
My thoughts were to apply a cement based render (as it's cheap) to stabilise the wall and provide a stable structure to affix an outer later to protect it from the elements eg cladding or rendered external insulation. The moisture then making it's way in over time and the walls drying out, and when it cracks in the future it will be largely protected . Or that there might be a more modern flexible and vapour permeable render that is lower maintenance than lime.
My issues with lime are that it's expensive, limited people use it hence longer lead times on labour, from my experience takes an age to dry out, increased maintennance, and with internally largely being plastered with modern plaster we are still going to have issues...
Not listed (wouldn't buy a listed property again!)
No wooden lintels left, previous farmers rather ingeniously managed to pour reinforced concrete lintels in situ. I know as we removed a load bearing wall and had to use a world of steel, and replace the nearest lintel with an RSJ as the engineer wasn't happy with the overlap.
Yes, cladding is kind of what I was getting at, but although not listed, it is in a conservation area, so easier if it doesn't materially alter the aesthetics.
I'll certainly get an old buildings guy in, but I imagine he will suggest lime, which is perhaps the way to go.
I appreciate that cement based render is completely wrong for the building, as it is impermeable, inflexible etc.
My thoughts were to apply a cement based render (as it's cheap) to stabilise the wall and provide a stable structure to affix an outer later to protect it from the elements eg cladding or rendered external insulation. The moisture then making it's way in over time and the walls drying out, and when it cracks in the future it will be largely protected . Or that there might be a more modern flexible and vapour permeable render that is lower maintenance than lime.
My issues with lime are that it's expensive, limited people use it hence longer lead times on labour, from my experience takes an age to dry out, increased maintennance, and with internally largely being plastered with modern plaster we are still going to have issues...
I m with Lotobear on this, about using an nhl 3 lime.
Bear in mind we ve seen no photos etc.
A mortar mix I have used on some stone buildings at the owners request is one part lime, one part masonry cement with five parts 0/2 or 0/4 sharp sand.
As with all surfaces, preparation is key for a good completion of works.
Bear in mind we ve seen no photos etc.
A mortar mix I have used on some stone buildings at the owners request is one part lime, one part masonry cement with five parts 0/2 or 0/4 sharp sand.
As with all surfaces, preparation is key for a good completion of works.
Edited by Magooagain on Sunday 1st February 11:26
Thanks for the input, sounds like lime is the way to go (bugger!)
I regularly drive past a place that specialises in supply of lime and associated stuff (https://roseofjericho.co.uk/) I'll pop in and get some recommendations on local tradesmen to have a look / quote. I am guessing that the walls will be in a pretty poor state once the current render is removed.
They mostly seem to stock / make their own stuff, one thing they do stock is "Cornerstone Insulating Render", NHL 2, seems to be suitable as a basecoat for crumbly walls. Any opinions on this?
Thanks
I regularly drive past a place that specialises in supply of lime and associated stuff (https://roseofjericho.co.uk/) I'll pop in and get some recommendations on local tradesmen to have a look / quote. I am guessing that the walls will be in a pretty poor state once the current render is removed.
They mostly seem to stock / make their own stuff, one thing they do stock is "Cornerstone Insulating Render", NHL 2, seems to be suitable as a basecoat for crumbly walls. Any opinions on this?
Thanks
Be careful - there's no end of BS written about old buildings that often really has very little basis in reality. It's become a whole cottage industry where so called experts spout no end of crap.
As a Geologist the most important question in my mind - what type of stone is the house made from? Highly permeable sponge like soft sandstone or almost completely impermeable and incredibly hard granite?
What’s true is not “lime is always right, cement is always wrong”, but rather:
Lime render is probably wise where the masonry is more vapour-open and weaker than cement.
Lime render isn't always beneficial where the masonry is dense and strong.
The stone’s hardness, porosity, and capillary behaviour are fundamental to how decisive the lime-vs-cement choice really is.
After all, endless old buildings here in Aberdeenshire are rendered with cement based harling but are bone dry inside - granite and gabro are unbelievably hard and impermeable on their own so what difference does the harling make?
As a Geologist the most important question in my mind - what type of stone is the house made from? Highly permeable sponge like soft sandstone or almost completely impermeable and incredibly hard granite?
What’s true is not “lime is always right, cement is always wrong”, but rather:
Lime render is probably wise where the masonry is more vapour-open and weaker than cement.
Lime render isn't always beneficial where the masonry is dense and strong.
The stone’s hardness, porosity, and capillary behaviour are fundamental to how decisive the lime-vs-cement choice really is.
After all, endless old buildings here in Aberdeenshire are rendered with cement based harling but are bone dry inside - granite and gabro are unbelievably hard and impermeable on their own so what difference does the harling make?
jmsgld said:
I appreciate that cement based render is completely wrong for the building, as it is impermeable, inflexible etc.
Worth bearing in mind as you consider your options that cement render isn't impermeable and becomes less so the weaker it is.It's not a back and white decision process.
Thanks for the input.
The problem areas are very porous and soft / loose, a lot of chalk interspersed with flint, very old and soft bricks, old lime mortar etc. There is some granite at corners / around some apertures etc. but sadly minimal. The current render isn't strong enough to support cladding / external insulation.
The problem is that the cement render has blown / cracked in many places and lets water in, then doesn't let it out as quickly, so comes inside.
My gut feeling is to protect the walls from driving rain but, also allow a vapour permeability so that they can dry out...
The not quite lime stuff (NHL) sounds like a plan then +- some cladding / external insulation. I only wish that it wasn't a 3 coat as it will undoubtedly cost more than I would like...
We could just patch the worst of the render in cement so that it is strong enough to take external insulation / cladding, hence protecting it from the elements, might take a few years to dry out though!
The problem areas are very porous and soft / loose, a lot of chalk interspersed with flint, very old and soft bricks, old lime mortar etc. There is some granite at corners / around some apertures etc. but sadly minimal. The current render isn't strong enough to support cladding / external insulation.
The problem is that the cement render has blown / cracked in many places and lets water in, then doesn't let it out as quickly, so comes inside.
My gut feeling is to protect the walls from driving rain but, also allow a vapour permeability so that they can dry out...
The not quite lime stuff (NHL) sounds like a plan then +- some cladding / external insulation. I only wish that it wasn't a 3 coat as it will undoubtedly cost more than I would like...
We could just patch the worst of the render in cement so that it is strong enough to take external insulation / cladding, hence protecting it from the elements, might take a few years to dry out though!
Snow and Rocks said:
After all, endless old buildings here in Aberdeenshire are rendered with cement based harling but are bone dry inside - granite and gabro are unbelievably hard and impermeable on their own so what difference does the harling make?
I would urge caution to your statement above, I don't disagree with what you have said but we could be at the point where the cement based harling is coming to the end of its life and a lot of properties which were treated to that in the 70s or 80s are now finding problems.I unfortunately found myself in that very position, house harled in the 70s or 80s by a previous owner and over time cracks and leaks from the tabling stones allowed water behind the harling which left damp marks on the inside.
when I began removing the harling there was no end of horrors lurking behind where water had washed the lime mortar out from the stone work leaving vast chasms behind the cement.
I have gone with the NL type lime repointing, which has largely been a success story but not perfect and having weather like we have right now is still able to drive moisture through in certain places and appears to be bleeding through solid granite type rock, but it is perhaps a capillary action through the mortar.
I think we have discussed before that I live a few miles along the road so you will be familiar with the weather we have been having this year.
I would def get it all off and let it breath, your approach seems good to protect but get that cement off and let it breath and moisture will always get in and not get out.
Cement when it s blown is the nemesis of old buildings. For some reassurance that getting it all off asap is the right thing to do and to 100% not patch it with any form of cement..:
We moved into an old sand stone barn a decade ago and about 190 sqm of walls had been cement pointed. With cement blowing in many places.
The damp was crazy, lots hidden and patched - internal plaster blowing within months etc, and all of the stone was crumbling and soft. We paid someone 10k for 8 weeks work (better man than me) to chisel out the cement, repoint with a lime mortar and patch in stones that were too far gone.
Night a day difference within months, as soon as walls could breath damp was 99% better, all stone stopped crumbling and went back to being firm.
Other hand neighbour went a different route and had their walls patched up and re pointed in cement. Damp has escalated considerably for them where is as largely none existent for us even the walls exposed to driving rain.
Lime is great stuff they look sodden some times but breathe it all back out unhindered.
Cement when it s blown is the nemesis of old buildings. For some reassurance that getting it all off asap is the right thing to do and to 100% not patch it with any form of cement..:
We moved into an old sand stone barn a decade ago and about 190 sqm of walls had been cement pointed. With cement blowing in many places.
The damp was crazy, lots hidden and patched - internal plaster blowing within months etc, and all of the stone was crumbling and soft. We paid someone 10k for 8 weeks work (better man than me) to chisel out the cement, repoint with a lime mortar and patch in stones that were too far gone.
Night a day difference within months, as soon as walls could breath damp was 99% better, all stone stopped crumbling and went back to being firm.
Other hand neighbour went a different route and had their walls patched up and re pointed in cement. Damp has escalated considerably for them where is as largely none existent for us even the walls exposed to driving rain.
Lime is great stuff they look sodden some times but breathe it all back out unhindered.
Edited by P155flaps on Monday 2nd February 23:53
Just be aware that all this 'breathing wall' malarkey is about heat leaving your walls along with a bit of water vapour.
In the absense of heat, a breathable wall will breathe both ways or the wrong way.
If you have an old building and wish to keep it authentic, then along with the limework, you need the authentic consumption of coal in the fires to drive the water through the walls. You can't really have the breathable porous stuff without some consequences in a building exposed to driving rain.
You have to take the whole package, you can't cherry pick the bits you like.
That may mean Aga-style gratuitous energy consumption to keep the place dry. That is how old buildings are designed/evolved to function.
Also be aware that old buildings often didn't work as well as modern ones. People accepted that walls got damp in storms and that it was cold in winter. It was normal for have a bit of damp and mold. People were happy to move away from all that and adopted cavity walls 100 years ago for very good reasons!
Alternatively, you could consider a more modern approach to the building, with some sort of rain screen and insulation to manage the water/vapour
It's easy to fall into the 'old ways were the best' trap. Problems include, the world has changed, heat is no longer cheap, energy waste is becoming less acceptable, expectations are different and arguably weather is getting more extreme more often.
Some 20+ years ago, I seriously looked into this, at the time there were interesting developments including insulating renders coming along. I haven't kept up with the progress though.
I have looked at a lot of damp houses in Devon. For things with no obvious moving parts, they are quite complex!
In the absense of heat, a breathable wall will breathe both ways or the wrong way.
If you have an old building and wish to keep it authentic, then along with the limework, you need the authentic consumption of coal in the fires to drive the water through the walls. You can't really have the breathable porous stuff without some consequences in a building exposed to driving rain.
You have to take the whole package, you can't cherry pick the bits you like.
That may mean Aga-style gratuitous energy consumption to keep the place dry. That is how old buildings are designed/evolved to function.
Also be aware that old buildings often didn't work as well as modern ones. People accepted that walls got damp in storms and that it was cold in winter. It was normal for have a bit of damp and mold. People were happy to move away from all that and adopted cavity walls 100 years ago for very good reasons!
Alternatively, you could consider a more modern approach to the building, with some sort of rain screen and insulation to manage the water/vapour
It's easy to fall into the 'old ways were the best' trap. Problems include, the world has changed, heat is no longer cheap, energy waste is becoming less acceptable, expectations are different and arguably weather is getting more extreme more often.
Some 20+ years ago, I seriously looked into this, at the time there were interesting developments including insulating renders coming along. I haven't kept up with the progress though.
I have looked at a lot of damp houses in Devon. For things with no obvious moving parts, they are quite complex!
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