Internal Lime Plaster on North facing gable wall

[CastonGuitar]

Hello Lime Plasterers!

3 years ago, we bought a flint cottage. The first job we did was repointing the whole external gable wall ( with sand and nhl 3.5 lime as we are only a couple of miles from the coast) as the mortar was cement-based instead of the original lime pointing.

We stripped the old gypsum plaster and filler off the internal gable end wall which runs up the staircase and into a small bedroom.

It took 2.5 years for it to dry out enough to contemplate re lime plastering.

We used slaked lime putty and pavior sand as a render before using watered-down putty as a whitewash paint.

We finished this job in the middle of Summer 2020, it looked excellent!

In September 2020, after living in the property for one month, with the central heating on, we experienced heavy driving rain on the north-facing gable wall. Within a day, large wet patches appeared on the wall both in the stairwell and the bedroom.
We've had the heating on full blast along with trying dehumidifiers but the walls remain wet, stained and flaking. After 4 full months of trying to dry it out, it seems to just keep sucking our moisture into the house.

We have bought a bag of casein lime filler to try out but the walls are still not dry enough for us to consider this.

I hope someone has some idea of where we have gone wrong and if it's possible for the rain to travel over 18 inches through the flint wall? We did think maybe it was condensation running down the wall from the poorly insulated roof but we had this redone in November with no change to the walls.

Although our aim was to make the wall breathable is this a mistake as it is a cold, north-facing wall?

Many thanks for any wisdom you may have!
Courtenay

 

[sewinelwy]

Hi, Courtenay,

firstly you've done the right things in the correct order! when you pointed the wall did you do it with an hydraulic lime mix using cement in a small proportion to the lime. Basically so it goes off quicker than a sand and lime mix would? did you rake out the stone work to remove all the loose and also deep enough to create a stable point which will stay in place and seal effectively? so first job is to check the pointing, make sure it is tight and no obvious movement or gaps around the stone.
Is the water penetration even throughout the wall? or in patches? or where?

You lime mortared the base coats with a sand putty mix, did you put hair into the mix?

other areas to check! is the roof sound is water running down the inside or outside or the roofing material and onto the top of the wall? On the gable end how is your waterproofing achieved and is that sound?

For clues look to this first:

water penetration mainly at the top of the building, generally roof or drainage issues. ie. are the gutters spilling onto the face of the wall.

water penetration mainly at ground level up to 1 meter high, rising damp caused by many things like drainage, outside ground level etc floors ie. have new solid floors been installed. Lime built houses of older property, solid walls of lime construction don't generally have a DPC, not needed as the lime morter is the solution. some later buildings might have but are usually slater.

Random and general penetration patches are through the walls or water getting behind the plaster.

look at these first and we'll take it from there!

One initial question, are the internal walls really pink or is that a trick of the light?

Le me know where you are on these points,.


Martin.

 

[Retired Spread]

@John j Bonding supremo he's the forums expert plastering old walls highly recommended

 

[Deleted member 32554]

@John j Bonding supremo he's the forums expert plastering old walls highly recommended

I'm dismayed at your outrageous favouritism in passing these jobs on to John

 

[worthwords]

Hello Lime Plasterers!

3 years ago, we bought a flint cottage. The first job we did was repointing the whole external gable wall ( with sand and nhl 3.5 lime as we are only a couple of miles from the coast) as the mortar was cement-based instead of the original lime pointing.

We stripped the old gypsum plaster and filler off the internal gable end wall which runs up the staircase and into a small bedroom.

It took 2.5 years for it to dry out enough to contemplate re lime plastering.

We used slaked lime putty and pavior sand as a render before using watered-down putty as a whitewash paint.

We finished this job in the middle of Summer 2020, it looked excellent!

In September 2020, after living in the property for one month, with the central heating on, we experienced heavy driving rain on the north-facing gable wall. Within a day, large wet patches appeared on the wall both in the stairwell and the bedroom.
We've had the heating on full blast along with trying dehumidifiers but the walls remain wet, stained and flaking. After 4 full months of trying to dry it out, it seems to just keep sucking our moisture into the house.

We have bought a bag of casein lime filler to try out but the walls are still not dry enough for us to consider this.

I hope someone has some idea of where we have gone wrong and if it's possible for the rain to travel over 18 inches through the flint wall? We did think maybe it was condensation running down the wall from the poorly insulated roof but we had this redone in November with no change to the walls.

Although our aim was to make the wall breathable is this a mistake as it is a cold, north-facing wall?

Many thanks for any wisdom you may have!
Courtenay

Hello Lime Plasterers!

3 years ago, we bought a flint cottage. The first job we did was repointing the whole external gable wall ( with sand and nhl 3.5 lime as we are only a couple of miles from the coast) as the mortar was cement-based instead of the original lime pointing.

We stripped the old gypsum plaster and filler off the internal gable end wall which runs up the staircase and into a small bedroom.

It took 2.5 years for it to dry out enough to contemplate re lime plastering.

We used slaked lime putty and pavior sand as a render before using watered-down putty as a whitewash paint.

We finished this job in the middle of Summer 2020, it looked excellent!

In September 2020, after living in the property for one month, with the central heating on, we experienced heavy driving rain on the north-facing gable wall. Within a day, large wet patches appeared on the wall both in the stairwell and the bedroom.
We've had the heating on full blast along with trying dehumidifiers but the walls remain wet, stained and flaking. After 4 full months of trying to dry it out, it seems to just keep sucking our moisture into the house.

We have bought a bag of casein lime filler to try out but the walls are still not dry enough for us to consider this.

I hope someone has some idea of where we have gone wrong and if it's possible for the rain to travel over 18 inches through the flint wall? We did think maybe it was condensation running down the wall from the poorly insulated roof but we had this redone in November with no change to the walls.

Although our aim was to make the wall breathable is this a mistake as it is a cold, north-facing wall?

Many thanks for any wisdom you may have!
Courtenay

if it's possible for the rain to travel over 18 inches through the flint wall?

Yes walls repeatedly hit by wind driven rain can eventually transmit moisture to the inside which is why cavity were first introduced around costal areas and islands. If it happened after just one episode then there must be some obvious penetrating water.
Always check gutters and go out when it rains to see what happens to the water - it's often surprising but iv'e seen walls that were like a waterfall due to poor shedding of water/overhang.

Given the history of problems. It does sound as if a core of the wall might be useful to see what its made of and how much the wet is.

Get a cheap temp and humidity logger Govee is £16 from amazon and you can monitor it from your phone over time to see what's happenign. Bear in mind if the wall is wet internally then increased relative humidity is going to be high as it's evaporating into the room.

Flint is hard and impermeable to water so the choice of external re-pointing mortar is important as there tends to be large amounts of lime mortar behind the irregylar shaped flints (which stick in like teeth into gums rather than flat cladding). If the external mortar prohibits the wall from drying between showers then that could also cause an issue. Apart from the fact that there's much variabiliy from suppliers in the strength of NHL 3.5 . We are now being told that after a year or two it could be as hard as NHL 10!
cl 90 (quicklime) hot lime mixes are much more predicable and aid in drying out walls (not 'breathable' but physically wick liquid to the wall surface for rapid evaporation.

 

[Retired Spread]

I'm dismayed at your outrageous favouritism in passing these jobs on to John

he gives me 10% commission on his day rate so I get 8 quid

 

[CastonGuitar]

Hi, Courtenay,

firstly you've done the right things in the correct order! when you pointed the wall did you do it with an hydraulic lime mix using cement in a small proportion to the lime. Basically so it goes off quicker than a sand and lime mix would? did you rake out the stone work to remove all the loose and also deep enough to create a stable point which will stay in place and seal effectively? so first job is to check the pointing, make sure it is tight and no obvious movement or gaps around the stone.
Is the water penetration even throughout the wall? or in patches? or where?

You lime mortared the base coats with a sand putty mix, did you put hair into the mix?

other areas to check! is the roof sound is water running down the inside or outside or the roofing material and onto the top of the wall? On the gable end how is your waterproofing achieved and is that sound?

For clues look to this first:

water penetration mainly at the top of the building, generally roof or drainage issues. ie. are the gutters spilling onto the face of the wall.

water penetration mainly at ground level up to 1 meter high, rising damp caused by many things like drainage, outside ground level etc floors ie. have new solid floors been installed. Lime built houses of older property, solid walls of lime construction don't generally have a DPC, not needed as the lime morter is the solution. some later buildings might have but are usually slater.

Random and general penetration patches are through the walls or water getting behind the plaster.

look at these first and we'll take it from there!

One initial question, are the internal walls really pink or is that a trick of the light?

Le me know where you are on these points,.


Martin.

Hi Martin, thanks for your in-depth reply!

Yes, the render was raked out on the external wall before re-pointing, it seems to be patches of damp for sure, as a few areas on the wall in the room shown in the photos are a really good finish, dry and how I expected it all to be, slightly powdery to the touch. There wasn't any hair put in the mix, is this a problem to have not done this?

The external wall has crow steps which were all replaced including the lead before we started the internal wall works. There are also no gutters along the top of that wall.

In the room show in the photo we re-rendered using NHL 3.5 and sharp same and then lime plastered with putty and fine sand for the finish. - just checked with our builder!

The stairwell wall is really that red/ pink. It's like brick bleeding through, quite bizarre! I don't think we stripped the gypsum off the wall in the stairwell, so this could have been one area we have gone wrong.
Thanks again
Courtenay

 

[worthwords]

Hi Martin, thanks for your in-depth reply!

Yes, the render was raked out on the external wall before re-pointing, it seems to be patches of damp for sure, as a few areas on the wall in the room shown in the photos are a really good finish, dry and how I expected it all to be, slightly powdery to the touch. There wasn't any hair put in the mix, is this a problem to have not done this?

The external wall has crow steps which were all replaced including the lead before we started the internal wall works. There are also no gutters along the top of that wall.

In the room show in the photo we re-rendered using NHL 3.5 and sharp same and then lime plastered with putty and fine sand for the finish. - just checked with our builder!

The stairwell wall is really that red/ pink. It's like brick bleeding through, quite bizarre! I don't think we stripped the gypsum off the wall in the stairwell, so this could have been one area we have gone wrong.
Thanks again
Courtenay

ah moisture + gypsum covered in lime doesn't sound good.

 

[CastonGuitar]

ah moisture + gypsum covered in lime doesn't sound good.

Yes, that could be the source of the red colour bleeding through the stair wall.
However, the other room at the top of the stairs, was taken right back before it was re-rendered with lime and then top coated with lime finish. (above images 2093 , 2094, 2095)

I've ordered the Govee from amazon! Looks like a good piece of kit, thanks for the recommendation.

So with the stairs it looks like a full chip off and another render+ finish- I read some stuff online about adding casein to a mix to help with binding.

Additives for Lime | Lime Stuff

Animal Hair when added to lime plaster helps binds it together and gives it additional tensile strength. The most commonly used is horse hair or goat hair which is usually about (2-3 inches) long and

www.limestuff.co.uk

Do you have an experience/ knowledge of this?

Thanks again

 

[CastonGuitar]

Hi all! I have been doing some more reading and came across this document

https://maclennanwaterproofing.co.uk/wp-content/uploads/2015/09/Maclennan-Plaster-lath-or-Lime.pdf

Anyone know anything about using plaster lath as a breathable membrane to fix to an internal wall and finish on the top of it?

This stuff!

Newton 805 Newlath Clear Meshed Plaster Membrane | In Stock

Newton 805 Newlath Clear Meshed Plaster Membrane available online with next day delivery. Plaster straight onto this membrane or use with plasterboard

www.restorationuk.com

Happy Sunday

 

[Brimstone]

I doff my cap to the lime specialists on here, but may I make a heretic suggestion of condensation? It's open plan, no door and all the warm air (plus cooking and a dryer maybe?) would go up there and condense on a chillingly cold flint wall.
Before plastering you might not have noticed it happening on stone, or maybe that was why it seemed to take so long to dry out. It seems a long while to dry out, it would surely have dried out externally first and drawn moisture away.
Do you have a door to the kitchen/scullery and is is kept closed, or do you leave it open to warm up the rest of the house?

 

[Brimstone]

Forgot to add - would also explain stairwall getting it bad and, above the doorway on what is not an external wall

 

[smoother09]

Move

 

[CastonGuitar]

I doff my cap to the lime specialists on here, but may I make a heretic suggestion of condensation? It's open plan, no door and all the warm air (plus cooking and a dryer maybe?) would go up there and condense on a chillingly cold flint wall.
Before plastering you might not have noticed it happening on stone, or maybe that was why it seemed to take so long to dry out. It seems a long while to dry out, it would surely have dried out externally first and drawn moisture away.
Do you have a door to the kitchen/scullery and is is kept closed, or do you leave it open to warm up the rest of the house?

Thanks for the reply, it does seem that maybe condensation could be the main problem. The flint wall is very thick and cold and I can see how higher humidity and heat in the house could condense onto the cold flint wall. If this is our main problem, is there anything realistically we can do about that.
The guy who did our lime plastering also thinks condensation may be at play.

It's warm downstairs as we have a pellet boiler in the kitchen so we dow have the doors open to send the heat through and up.

Thanks again
Courtenay

 

[Brimstone]

It needs the flint wall to be isolated from the heat as you will never get it warm enough to prevent condensation, and you need to reduce the moisture content in the air.
In rentals excess moisture is typically caused by cooking with the kitchen door open and dryers/hanging wet clothes (Even the condensing dryer sort let out moist air.) Heavy drape curtain at bottom of the stairs also works quite well.
Keep the doors to upstairs closed until say 1/2hr before bed, and close them before you go to bed to prevent fire and smoke spread. A smoke alarm upstairs is a good thing. Old bedrooms used to have vents in them to reduce condensation caused by the sleeping occupants at night. Yes, cold - more blankets, bedclothes etc. old style. A radiator off the boiler would help but not solve the issue.
Flint wall/doorway head - install a door and insulated plasterboard and battens, (must be with a vapour barrier) maybe, wall can then only dry one side but should be ok unless there is a faulty channel for water to get in.

 

[Deleted member 32554]

It needs the flint wall to be isolated from the heat as you will never get it warm enough to prevent condensation, and you need to reduce the moisture content in the air.
In rentals excess moisture is typically caused by cooking with the kitchen door open and dryers/hanging wet clothes (Even the condensing dryer sort let out moist air.) Heavy drape curtain at bottom of the stairs also works quite well.
Keep the doors to upstairs closed until say 1/2hr before bed, and close them before you go to bed to prevent fire and smoke spread. A smoke alarm upstairs is a good thing. Old bedrooms used to have vents in them to reduce condensation caused by the sleeping occupants at night. Yes, cold - more blankets, bedclothes etc. old style. A radiator off the boiler would help but not solve the issue.
Flint wall/doorway head - install a door and insulated plasterboard and battens, (must be with a vapour barrier) maybe, wall can then only dry one side but should be ok unless there is a faulty channel for water to get in.

I've never understood the need for a vapour barrier if boards are gapped and foam filled

 

[ChrispyUK]

It needs the flint wall to be isolated from the heat as you will never get it warm enough to prevent condensation, and you need to reduce the moisture content in the air.
In rentals excess moisture is typically caused by cooking with the kitchen door open and dryers/hanging wet clothes (Even the condensing dryer sort let out moist air.) Heavy drape curtain at bottom of the stairs also works quite well.
Keep the doors to upstairs closed until say 1/2hr before bed, and close them before you go to bed to prevent fire and smoke spread. A smoke alarm upstairs is a good thing. Old bedrooms used to have vents in them to reduce condensation caused by the sleeping occupants at night. Yes, cold - more blankets, bedclothes etc. old style. A radiator off the boiler would help but not solve the issue.
Flint wall/doorway head - install a door and insulated plasterboard and battens, (must be with a vapour barrier) maybe, wall can then only dry one side but should be ok unless there is a faulty channel for water to get in.

some chunt has just kicked the bathroom door off.

 

[Brimstone]

I've never understood the need for a vapour barrier if boards are gapped and foam filled

moisture evaporates into a gas ("vapour") which then passes thru most things then condenses on the other side, most probably inside the gap, depends on where the temperature point (dew point) changes on its way from warm side to cold side.

 

[Deleted member 32554]

moisture evaporates into a gas ("vapour") which then passes thru most things then condenses on the other side, most probably inside the gap, depends on where the temperature point (dew point) changes on its way from warm side to cold side.

Do you consider moisture on the back of a foam board to be a problem

 

[Brimstone]

Do you consider moisture on the back of a foam board to be a problem

Unfortunately yes - mold spores love it, and somehow the stink gets out into the room after a time. Can have other ramifications aswell.
If it's something that only gets heated sometimes, like a garage, then its less of a problem. I sealed the edges of the sheets of celotec under the garage roof and left a void in the middle - it'll mold etc but DILLIGAF, I don't live in there (unless the missus has a major turn)

 

[Deleted member 32554]

Unfortunately yes - mold spores love it, and somehow the stink gets out into the room after a time. Can have other ramifications aswell.

Personally wouldn't use wooden battens

but DILLIGAF, I don't live in there (unless the missus has a major turn)

I go up the field lol

 

[Brimstone]

Personally wouldn't use wooden battens

I go up the field lol

only treated ones, how do you gap it without - screws into the wall? I've done that several times in fireplaces.

I might be up there some time....I'll take garage or the sheds over a tent

 

[Deleted member 32554]

only treated ones, how do you gap it without - screws into the wall? I've done that several times in fireplaces.

Foam with some fire fixing screws

 

[worthwords]

Thanks for the reply, it does seem that maybe condensation could be the main problem. The flint wall is very thick and cold and I can see how higher humidity and heat in the house could condense onto the cold flint wall. If this is our main problem, is there anything realistically we can do about that.
The guy who did our lime plastering also thinks condensation may be at play.

It's warm downstairs as we have a pellet boiler in the kitchen so we dow have the doors open to send the heat through and up.

Thanks again
Courtenay

my advice is don't do anything on the back of a 'i reckon it's x' response. We have the tools and means to diagnose damp and i dread to think the millions of wasted pounds in the uk spent on 'solutions' when a diagnosis have never been made.
I've heard of walls having 10x damp proof solutions when it was just roofing detail or blocked drain.

Have a watch ....

 

[limeplastering]

Hi how many of coats of nhl did you do how long did you leave it between coats and what ratio did you use?

 

[Brimstone]

my advice is don't do anything on the back of a 'i reckon it's x' response. We have the tools and means to diagnose damp and i dread to think the millions of wasted pounds in the uk spent on 'solutions' when a diagnosis have never been made.
I've heard of walls having 10x damp proof solutions when it was just roofing detail or blocked drain.

Have a watch ....

I don't disagree with what you are saying but this is not rising damp and the poster is clearly aware of the roofing issues and discounted them. Robyn in other papers actually confirms exactly what I have suggested. Curiously, she also mentions the original traditional solution to this which I had forgotten, remembered, and will pm to the OP - wood panelling.

 

[BryanJ]

I would go for condensation, put some foil paper over a section to see if you have moisture on the inside or outside of the foil. Traditional the house would have had an open fire which helps air circulation. Central heating, sealed window and draught proofing all reduce air circulation. Interstitial condensation looks like penetrating damp. The reason I would not think its penetrating through the wall is the height of the dampness, the low parts of the wall would be a lot wetter. Its only my best guess.
There are ceiling ventilation fans, wired off ceiling lights, low noise that kicking in to help air circulation, kick in when air moisture level are high.

 

[worthwords]

I don't disagree with what you are saying but this is not rising damp and the poster is clearly aware of the roofing issues and discounted them. Robyn in other papers actually confirms exactly what I have suggested. Curiously, she also mentions the original traditional solution to this which I had forgotten, remembered, and will pm to the OP - wood panelling.

yes i know it's not rising damp. more a general principle of invetigation rather than assumptionsFrom the follow on information there's likely several contributing factors.

 

[limeplastering]

I have only really seen one case of this and I think it’s a build up of salts in the wall. I did how ever get over this removed all plaster work used a Newton tanking membrane and nhl 3 coat lime on top not really ideal but did work in the long run