Lime plaster on damp brick walls

RenovationHelp

New Member
I'm renovating an 1890s solid brick walled terrace. The builder has ripped off the internal gypsum plaster and found that the walls are damp in a number of places. My feeling is that the house won't have been breathing due to (cracked) external cement render, the inappropriate internal plaster, upvc windows without trickle vents and the previous owner being an elderly lady. There are some obvious causes of water - A drain pipe discharging down the wall, a leak from the bath etc. so I feel like it just needs to be either heated and ventilated for a bit or use a dehumidifier.

Our contractors have been trying to persuade me to use gypsum rather than lime through the whole project and are now using the damp walls to press their case. So my question is, can you lime plaster over damp brick? I assume that as long as I remove the cement render and replace it with lime (due to happen in spring) it should eventually dry out even if plastered.

If not, should we try drying out the brick and how long might that take? Or should I just give in and use modern materials?

Any advice very welcome!
 

superspread

Well-Known Member
I'm renovating an 1890s solid brick walled terrace. The builder has ripped off the internal gypsum plaster and found that the walls are damp in a number of places. My feeling is that the house won't have been breathing due to (cracked) external cement render, the inappropriate internal plaster, upvc windows without trickle vents and the previous owner being an elderly lady. There are some obvious causes of water - A drain pipe discharging down the wall, a leak from the bath etc. so I feel like it just needs to be either heated and ventilated for a bit or use a dehumidifier.

Our contractors have been trying to persuade me to use gypsum rather than lime through the whole project and are now using the damp walls to press their case. So my question is, can you lime plaster over damp brick? I assume that as long as I remove the cement render and replace it with lime (due to happen in spring) it should eventually dry out even if plastered.

If not, should we try drying out the brick and how long might that take? Or should I just give in and use modern materials?

Any advice very welcome!
Let the walls dry out for a bit , then use lime 100%
 

hstoke

Well-Known Member
I'm renovating an 1890s solid brick walled terrace. The builder has ripped off the internal gypsum plaster and found that the walls are damp in a number of places. My feeling is that the house won't have been breathing due to (cracked) external cement render, the inappropriate internal plaster, upvc windows without trickle vents and the previous owner being an elderly lady. There are some obvious causes of water - A drain pipe discharging down the wall, a leak from the bath etc. so I feel like it just needs to be either heated and ventilated for a bit or use a dehumidifier.

Our contractors have been trying to persuade me to use gypsum rather than lime through the whole project and are now using the damp walls to press their case. So my question is, can you lime plaster over damp brick? I assume that as long as I remove the cement render and replace it with lime (due to happen in spring) it should eventually dry out even if plastered.

If not, should we try drying out the brick and how long might that take? Or should I just give in and use modern materials?

Any advice very welcome!
Lime for that ,definitely no gypsum !!!!
do your research online about lime and it’s uses in old properties
 

RenovationHelp

New Member
Lime for that ,definitely no gypsum !!!!
do your research online about lime and it’s uses in old properties
I have - I'm just struggling with all the contractors saying it is a bad idea! I'm keen to use lime but they're saying that we can't wait for the bricks to dry out and that if we used gypsum we wouldn't have to.

I really just wanted to check my assumptions that if we genuinely can't get the bricks dry beforehand (which is still my hope), it could dry under the lime plaster eventually as it will breath. I'm not sure how long I can delay for drying although I'm certainly going to push for longer and some use of a dehumidifier or heating and ventilation or something (ideas welcome!)
 

hstoke

Well-Known Member
I have - I'm just struggling with all the contractors saying it is a bad idea! I'm keen to use lime but they're saying that we can't wait for the bricks to dry out and that if we used gypsum we wouldn't have to.

I really just wanted to check my assumptions that if we genuinely can't get the bricks dry beforehand (which is still my hope), it could dry under the lime plaster eventually as it will breath. I'm not sure how long I can delay for drying although I'm certainly going to push for longer and some use of a dehumidifier or heating and ventilation or something (ideas welcome!)
U don’t wait for it too dry out it will dry naturally , yer wet the walls when u apply lime ,that builder is taking the piss and doesn’t want the extra expense of lime ,as long as isn't running like a stream down the walls crack on with it
With somebody who knows what they r doing
 

Brimstone

Well-Known Member
"They can't Wait"? Who's paying the bill - you are. Sounds like they were going to do it themselves and have no idea about lime. Or they have a skimmer not a plasterer.- in which case there might be a delay finding one.
Yes it will take longer, and cost a bit more, plus drying time - but all that should delay is the decorating. There shouldn't be anything that the builder still has to do that he cannot get on with.
 

RenovationHelp

New Member
"They can't Wait"? Who's paying the bill - you are. Sounds like they were going to do it themselves and have no idea about lime. Or they have a skimmer not a plasterer.- in which case there might be a delay finding one.
Yes it will take longer, and cost a bit more, plus drying time - but all that should delay is the decorating. There shouldn't be anything that the builder still has to do that he cannot get on with.
I've already agreed a much higher price for plaster because I wanted to use lime so it won't cost them any more (although I think I'd better ask to meet their plasterer)!
 

superspread

Well-Known Member
Do you have any idea how long that might take? The old plaster has been off for a couple of weeks and they tell me that there's been no improvement. Thanks!
You could get the backing coat done , but if the walls are as wet as you say it could mess up when it comes to the lime finish!but the plasterer should know when it’s the right time to put the setting stuff on
 

Stewie03

Well-Known Member
Get some pics on of the walls and bricks been 6 months since I've seen anything damp since the missus slung out baby number 3
 
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RenovationHelp

New Member
You could get the backing coat done , but if the walls are as wet as you say it could mess up when it comes to the lime finish!but the plasterer should know when it’s the right time to put the setting stuff on
They're damp but your hand doesn't come away wet from the wall. I've told them to investigate dehumidifiers or heating and opening windows before we consider doing anything other than using lime. Hopefully it won't take too long!
 

RenovationHelp

New Member
Lastest update:
Just be warned it may take several years before you can decorate some of the areas that are damp without remedial treatment.

Surely that can't be right? I've seen an inch a month given as a guideline. Is that miles off?
 

leefaithfull

Active Member
It is coming off in the spring but I couldn't find anyone who had capacity to render in lime before it gets too cold so can't do anything about that for now!
i dont suppose the inside can wait until spring then ?, that would be the wise thing to do,,if not de humidifier to dry damp out and use lime inside only,,the render has to come off and replaced with lime as you have wisely said, do not use modern plaster inside
 

RenovationHelp

New Member
i dont suppose the inside can wait until spring then ?, that would be the wise thing to do,,if not de humidifier to dry damp out and use lime inside only,,the render has to come off and replaced with lime as you have wisely said, do not use modern plaster inside
Unfortunately not - we can wait to decorate but the main building work should be finished in January (unless we have additional issues)
 

RenovationHelp

New Member
I've now been told that there has been soot leakage into the bricks of the chimney breast and that the stain will come through the lime plaster if it isn't sealed with bitumen paint under the lime!
 

leefaithfull

Active Member
Unfortunately not - we can wait to decorate but the main building work should be finished in January (unless we have additional issues)

I've now been told that there has been soot leakage into the bricks of the chimney breast and that the stain will come through the lime plaster if it isn't sealed with bitumen paint under the lime!
you need to scrub soot off of bricks,,then treat it with a vinegar and water mix 50/50,,,then scrub soot off with wire brush, repeat if necessary my old mucker,,if you bitumen it you may have troubles with breathing again
 

RenovationHelp

New Member
you need to scrub soot off of bricks,,then treat it with a vinegar and water mix 50/50,,,then scrub soot off with wire brush, repeat if necessary my old mucker,,if you bitumen it you may have troubles with breathing again
Honestly, I'm starting to wonder if the soot is imaginary and they're just trying to get me to agree to gypsum because if there is soot, it isn't enough that I'd noticed it! I've got a site meeting Monday so will have a look at the chimneys then and see if I can spot the soot and discuss whether they've considered the concept of cleaning the bricks!
 

limeplastering

Active Member
Bitumen would not stick to soot and is not appropriate for your building it is the worse possible thing you could do worse then your sand cement render.
Gypsum will absorb like a sponge and sand and cement will trap the moisture so you have the second worse situation ( apart from having a timber frame )
Your builder must be stupid to think removing damp gypsum and replacing it with more gypsum will solve the problem.
Get a local specialist in we do house purchase / renovation surveys so I am sure you should find some one near you.
Don’t let a chancer have a go and always get a detailed specification before they start …. So many firms by us saying use lime mortar just because they stick a bucket of hydrate in there sand and cement!
 

RenovationHelp

New Member
you need to scrub soot off of bricks,,then treat it with a vinegar and water mix 50/50,,,then scrub soot off with wire brush, repeat if necessary my old mucker,,if you bitumen it you may have troubles with breathing again
Yea, I can't really see the point of putting lime plaster on so the bricks can breathe but putting something impermeable under the lime ‍♀️ Maybe if it was a tiny percentage of the walls it wouldn't be a disaster but seems like a bad starting point!

I've found this: https://www.lime.org.uk/isolating-primer-earthborn.html so if just cleaning isn't enough, maybe we can try this!
 

RenovationHelp

New Member
Bitumen would not stick to soot and is not appropriate for your building it is the worse possible thing you could do worse then your sand cement render.
Gypsum will absorb like a sponge and sand and cement will trap the moisture so you have the second worse situation ( apart from having a timber frame )
Your builder must be stupid to think removing damp gypsum and replacing it with more gypsum will solve the problem.
Get a local specialist in we do house purchase / renovation surveys so I am sure you should find some one near you.
Don’t let a chancer have a go and always get a detailed specification before they start …. So many firms by us saying use lime mortar just because they stick a bucket of hydrate in there sand and cement!
It is really odd because one of the reasons I went with them is that they've done work to listed buildings including lime rendering so I thought they'd understand old buildings and might be able to find appropriate plasterers!
I contacted about 40-50 people and almost no one did lime work, of those who did one guy said he helped do some when he was doing his apprenticeship & would give it a go, one was drunk at 10am, three never gave me a quote at all and one did eventually give a quote and seemed fine but was booked until 2023!
 

leefaithfull

Active Member
Yea, I can't really see the point of putting lime plaster on so the bricks can breathe but putting something impermeable under the lime ‍♀️ Maybe if it was a tiny percentage of the walls it wouldn't be a disaster but seems like a bad starting point!

I've found this: https://www.lime.org.uk/isolating-primer-earthborn.html so if just cleaning isn't enough, maybe we can try this!
Yea, I can't really see the point of putting lime plaster on so the bricks can breathe but putting something impermeable under the lime ‍♀️ Maybe if it was a tiny percentage of the walls it wouldn't be a disaster but seems like a bad starting point!

I've found this: https://www.lime.org.uk/isolating-primer-earthborn.html so if just cleaning isn't enough, maybe we can try this!
spoy on
 

limeplastering

Active Member
It is really odd because one of the reasons I went with them is that they've done work to listed buildings including lime rendering so I thought they'd understand old buildings and might be able to find appropriate plasterers!
I contacted about 40-50 people and almost no one did lime work, of those who did one guy said he helped do some when he was doing his apprenticeship & would give it a go, one was drunk at 10am, three never gave me a quote at all and one did eventually give a quote and seemed fine but was booked until 2023!
Where abouts are you based the might be some one on here close by?
 

hstoke

Well-Known Member
Yea, I can't really see the point of putting lime plaster on so the bricks can breathe but putting something impermeable under the lime ‍♀️ Maybe if it was a tiny percentage of the walls it wouldn't be a disaster but seems like a bad starting point!

I've found this: https://www.lime.org.uk/isolating-primer-earthborn.html so if just cleaning isn't enough, maybe we can try this!
We’ve told previously on this thread that builder of yours is a pee taker and doesn’t know s**t
 

RenovationHelp

New Member
Quick update in case anyone is interested! Finally met the plasterer today and he seems to know his stuff - none of this bitumen nonsense came from him!

We've agreed to put dehumidifiers in for a few weeks before he starts and see how we go from there.

Thanks everyone for your advice
 
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