Lime plaster - yes or no
Discussion
Here is one for the Victorian house experts.
My daughter has bought a 2up 2down Victorian terraced house. It has a bedroom and a bathroom upstairs and that’s it. The house was built in 1860 and has lime mortar. We are gutting it back to the bricks and refurbing completely as it was in such a state. It’s a great Dad and daughter project.
Upstairs is the next stage. The original lime plaster has been over skimmed with modern but that is all coming off down to the bricks as the plaster underneath is in a very poor state.
The question is do I get the walls lime plastered or cement plastered?
The house has been recently repointed with modern mortar and the downstairs was well done but in modern plaster.
I think my thinking is half the house has been done with modern materials, which maybe shouldn’t have been used. Will it make a difference if I do the upstairs properly given the pointing is modern too, so the majority of the house ‘breathing’ has already been compromised.
Or am I just over thinking this?
Any advice very much appreciated.
My daughter has bought a 2up 2down Victorian terraced house. It has a bedroom and a bathroom upstairs and that’s it. The house was built in 1860 and has lime mortar. We are gutting it back to the bricks and refurbing completely as it was in such a state. It’s a great Dad and daughter project.
Upstairs is the next stage. The original lime plaster has been over skimmed with modern but that is all coming off down to the bricks as the plaster underneath is in a very poor state.
The question is do I get the walls lime plastered or cement plastered?
The house has been recently repointed with modern mortar and the downstairs was well done but in modern plaster.
I think my thinking is half the house has been done with modern materials, which maybe shouldn’t have been used. Will it make a difference if I do the upstairs properly given the pointing is modern too, so the majority of the house ‘breathing’ has already been compromised.
Or am I just over thinking this?
Any advice very much appreciated.
Does it have a cavity? If not then I would want as little modern material as I could get away with. Concrete pointing and gypsum plaster is almost certainly going to cause issues. But you have it downstairs already so upstairs would be less critical. Personally I'd be using lime and breathable paint as you have the opportunity to. Downstairs is just a watch and wait, no issues then sit tight, if it gets damp then sadly something would have to change. I'd start with the pointing as it's less disruptive.
I've found just stripping off layers of emulsioned wallpaper makes a surprising amount of difference so every bit helps.
I've found just stripping off layers of emulsioned wallpaper makes a surprising amount of difference so every bit helps.
A bit of a halfway house between modern gypsum plasters/cement and full on lime nazi, who’d have you believe there were no issues with damp in houses before the former arrived on the scene; Limelight renovating plasters.
My feeling is that you won't keep a typical solid brick terrace house dry just by choosing a different plaster or pointing.
Traditionally, a single skin house actually works by having a fire in the hearth 9 months of the year.
That puts heat in and creates airflow.
Heat is leaving the walls, taking water vapour with it.
If you want to do things the old way, you have to do the whole 19th century thing, not cherry pick expensive mud for the walls.
Not all brick terraced houses are the same. Bricks are very variable. Climate is very variable, the South Coast is quite different from the North.
Building details vary too.
All this water people want to 'breathe from the walls', where is it coming from? Is it coming in, rain penetration and rising damp, or is it mostly internally generated? The former is helped by moisture breathing in to a well ventilated (AKA draughty) interior, the latter is made worse which is why modern houses have moisture barriers on the back of the dry lining.
The redeeming feature of small terraced houses is that they don't actually have much area of exterior wall. Mine had even less when I tacked on a 'soweto style' conservatory, bringing the most troublesome wall in out of the weather!
My opinion is that mostly, good heat and ventilation are key, details of materials less so. Minimising the unwanted ingress of water is a priority, sort the roof out (joins with next door being a common nightmare), try to keep the bottom of the walls dry, make sure the pointing works, consider a rain-repellant coating on the bricks maybe. Make sure the gutters work properly. Control interior moisture from cooking, showers etc.
Dehumdifier is worth considering.
The other thing about lime mortar is that it allows movement to some extent which is a whole other can of worms...
Traditionally, a single skin house actually works by having a fire in the hearth 9 months of the year.
That puts heat in and creates airflow.
Heat is leaving the walls, taking water vapour with it.
If you want to do things the old way, you have to do the whole 19th century thing, not cherry pick expensive mud for the walls.
Not all brick terraced houses are the same. Bricks are very variable. Climate is very variable, the South Coast is quite different from the North.
Building details vary too.
All this water people want to 'breathe from the walls', where is it coming from? Is it coming in, rain penetration and rising damp, or is it mostly internally generated? The former is helped by moisture breathing in to a well ventilated (AKA draughty) interior, the latter is made worse which is why modern houses have moisture barriers on the back of the dry lining.
The redeeming feature of small terraced houses is that they don't actually have much area of exterior wall. Mine had even less when I tacked on a 'soweto style' conservatory, bringing the most troublesome wall in out of the weather!
My opinion is that mostly, good heat and ventilation are key, details of materials less so. Minimising the unwanted ingress of water is a priority, sort the roof out (joins with next door being a common nightmare), try to keep the bottom of the walls dry, make sure the pointing works, consider a rain-repellant coating on the bricks maybe. Make sure the gutters work properly. Control interior moisture from cooking, showers etc.
Dehumdifier is worth considering.
The other thing about lime mortar is that it allows movement to some extent which is a whole other can of worms...
Lime plaster isn't a 'solve everything's. You need full system of breathable mortar, breathable paints breathable stone etc.
It also doesn't shift anywhere like the volume of moisture modern life or a leaky gutter can input into a wall or room.
Focus more on keeping water out with good gutters and french drains, reducing moisture inside through behaviours and ventilation via fan and windows.
You can get modern like plasters that are easy and cheap - I used to sell https://baumit.co.uk/products/internal-plasters
It also doesn't shift anywhere like the volume of moisture modern life or a leaky gutter can input into a wall or room.
Focus more on keeping water out with good gutters and french drains, reducing moisture inside through behaviours and ventilation via fan and windows.
You can get modern like plasters that are easy and cheap - I used to sell https://baumit.co.uk/products/internal-plasters
You don't want condensation accumulating on the walls in your rooms. You don't want water trapped in the wall. You don't want the pointing or the mortar between the bricks to be stronger than the bricks.
Three separate requirements.
Lime mortars can solve the strength problem. That one at least is fairly simple.
Condensation is a function of the humidity of the air in the building and the difference in temperature between the internal wall surface and the air in the room. Accumulation of condensation is also a function of how much water the internal wall surface can absorb. You can reduce condensation by reducing the temperature difference ... i.e. make the air temperature colder, or make the wall surface warmer (by insulating it, by having a radiator on it). You can reduce accumulation by making the wall surface absorbent, e.g. breathable paint, breathable wall paper, no gypsum plaster. And you can use ventilation to reduce the humidity of the air in the room, and to remove condensation after a blast of humidity, as in a bathroom.
You stop water from getting trapped in your walls by allowing it to escape quicker than it accumulates. So, where possible, stop it getting in in the first place. But you then need to consider how it is going to get out. Cavity walls with air circulation in the cavity allow walls to dry from within. A solid wall needs to be able to evaporate water either externally, internally or on both sides. Lime mortars breath better than cement mortars, hence why they get used for external pointing and internal plastering.
So it is just a somewhat complicated problem. There are quite a few moving parts.
Here's an option to consider for your upstairs rooms. Strip back to the brickwork and don't replaster at all. That will maximise the wall's ability to evaporate into the interior, helping to keep the bulk of the wall dry. Fix battens to the wall to create an air gap and ensure that air can circulate through it. Then fix insulation board to the battening. You can either design your wall to have breathable internal insulation, plaster and paints, or you can try to make the internal side impervious and lean more on internal ventilation. I think the latter strategy is a bit higher risk.
Lots of combinations can work. There isn't one obviously correct way to tackle these things
There are however strategies that are clearly guaranteed to fail and that is all about trapping water in inappropriate places.
The pros and cons really boil down to:
Lime somewhat reduces the risk of trapping water.
Modern cement and plaster are quicker and easier to use.
I'll attach some photos showing the result of using materials completely inappropriately a bit later once I've got togged up for wading through and breathing filth.
Three separate requirements.
Lime mortars can solve the strength problem. That one at least is fairly simple.
Condensation is a function of the humidity of the air in the building and the difference in temperature between the internal wall surface and the air in the room. Accumulation of condensation is also a function of how much water the internal wall surface can absorb. You can reduce condensation by reducing the temperature difference ... i.e. make the air temperature colder, or make the wall surface warmer (by insulating it, by having a radiator on it). You can reduce accumulation by making the wall surface absorbent, e.g. breathable paint, breathable wall paper, no gypsum plaster. And you can use ventilation to reduce the humidity of the air in the room, and to remove condensation after a blast of humidity, as in a bathroom.
You stop water from getting trapped in your walls by allowing it to escape quicker than it accumulates. So, where possible, stop it getting in in the first place. But you then need to consider how it is going to get out. Cavity walls with air circulation in the cavity allow walls to dry from within. A solid wall needs to be able to evaporate water either externally, internally or on both sides. Lime mortars breath better than cement mortars, hence why they get used for external pointing and internal plastering.
So it is just a somewhat complicated problem. There are quite a few moving parts.
Here's an option to consider for your upstairs rooms. Strip back to the brickwork and don't replaster at all. That will maximise the wall's ability to evaporate into the interior, helping to keep the bulk of the wall dry. Fix battens to the wall to create an air gap and ensure that air can circulate through it. Then fix insulation board to the battening. You can either design your wall to have breathable internal insulation, plaster and paints, or you can try to make the internal side impervious and lean more on internal ventilation. I think the latter strategy is a bit higher risk.
Lots of combinations can work. There isn't one obviously correct way to tackle these things
There are however strategies that are clearly guaranteed to fail and that is all about trapping water in inappropriate places.
The pros and cons really boil down to:
Lime somewhat reduces the risk of trapping water.
Modern cement and plaster are quicker and easier to use.
I'll attach some photos showing the result of using materials completely inappropriately a bit later once I've got togged up for wading through and breathing filth.
We live in a 1870 victorian end of terrace.
Next door complained when first moved in that they were getting damp and asked us if we had any. We don’t.
Every morning we open any bedroom window that was occupied and leave the doors open to allow air to circulate.
If its really cold and grim outside I stick a dehumidifier on for an hour.
In old houses like this drafts are your friend it keeps the moist air moving. The trade off is higher heating bills.
Work with the building and its fine. Fight it and it gets costly.
Next door complained when first moved in that they were getting damp and asked us if we had any. We don’t.
Every morning we open any bedroom window that was occupied and leave the doors open to allow air to circulate.
If its really cold and grim outside I stick a dehumidifier on for an hour.
In old houses like this drafts are your friend it keeps the moist air moving. The trade off is higher heating bills.
Work with the building and its fine. Fight it and it gets costly.
I went the other way and did internal wall insulation with the warm batten method ie 50mm pir tight to the wall, taped joints to form a vapour barrier and then 50x25 batten over the top with 12.5mm plasterboard over that.
Outside was rendered and painted, it had had a recent damp course installation and there were no signs of previous damp.
I installed properly size ventilation in the kitchen and bathrooms, had a multi fuel stove and brings family house, we were always in and out so the house could breath pretty well.
Had no issues at all in the 6 years we lived there, the house was very warm - the stove kept the whole house warm in the depths of winter without the need for the boiler.
You can get breathable, waterproof coatings for brickwork, if you apply this to the outside I would be pretty confident with putting PIR to the internal walls without problems.
Outside was rendered and painted, it had had a recent damp course installation and there were no signs of previous damp.
I installed properly size ventilation in the kitchen and bathrooms, had a multi fuel stove and brings family house, we were always in and out so the house could breath pretty well.
Had no issues at all in the 6 years we lived there, the house was very warm - the stove kept the whole house warm in the depths of winter without the need for the boiler.
You can get breathable, waterproof coatings for brickwork, if you apply this to the outside I would be pretty confident with putting PIR to the internal walls without problems.
PistonHeads delivers again! Many thanks for the input everyone. I spent about 3hrs on Saturday with an SDS plus drill and managed to get almost all the over plastered original material off the wall. Jesus what a load of dust! The rest will be done in a few days time when the neighbours are out at work!
I love a bit of house archeology and it’s really my interesting to see where previous owners have left their own traces. Evidence of old cupboards and so on.
I love a bit of house archeology and it’s really my interesting to see where previous owners have left their own traces. Evidence of old cupboards and so on.
The timberwork is 15th/16th century. It looks like it's been infilled with 19th century brick on the inside. The external face of the wall is C18th brick. To the left of the window some nutcase "plastered" the wall with ... concrete. It's up to 6" thick in places. Weighs a ton.
The woodwork appears to have been lime washed. At some point it has been keyed to take plaster. The brickwork was originally lime/horsehair plastered. There's ocre limewash on that surface and then wall paper. And then more recently it has either been buried under concrete or skimmed with gypsum and then painted with something plasticy. The waterproof layers on the inside have contributed to the lime separating from the brick and, more seriously, to some deterioration in the timberwork.
Externally we've already extended the roof further over the gable end, replaced the fascia boards, repointed in lime, and put a flaunch on the top of some brick string coarses to get them to shed water away from the wall.
Internally we'll insulate the walls with lime and hemp and use wool board then lime and hemp to make a ceiling. More insulation will go on top and between the rafters. And we'll decorate using chalk-based paint.
The woodwork appears to have been lime washed. At some point it has been keyed to take plaster. The brickwork was originally lime/horsehair plastered. There's ocre limewash on that surface and then wall paper. And then more recently it has either been buried under concrete or skimmed with gypsum and then painted with something plasticy. The waterproof layers on the inside have contributed to the lime separating from the brick and, more seriously, to some deterioration in the timberwork.
Externally we've already extended the roof further over the gable end, replaced the fascia boards, repointed in lime, and put a flaunch on the top of some brick string coarses to get them to shed water away from the wall.
Internally we'll insulate the walls with lime and hemp and use wool board then lime and hemp to make a ceiling. More insulation will go on top and between the rafters. And we'll decorate using chalk-based paint.
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