Lime plaster on damp brick walls

R

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!
 
RenovationHelp said:
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!
Click to expand...
Let the walls dry out for a bit , then use lime 100%
 
RenovationHelp said:
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!
Click to expand...
Lime for that ,definitely no gypsum !!!!
do your research online about lime and it’s uses in old properties
 
hstoke said:
Lime for that ,definitely no gypsum !!!!
do your research online about lime and it’s uses in old properties
Click to expand...
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!)
 
RenovationHelp said:
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!)
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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
 
"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.
 
Brimstone said:
"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.
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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)!
 
RenovationHelp said:
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!
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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
 
superspread said:
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
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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!
 
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?
 
RenovationHelp said:
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!
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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
 
leefaithfull said:
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
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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!
 
RenovationHelp said:
Unfortunately not - we can wait to decorate but the main building work should be finished in January (unless we have additional issues)
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RenovationHelp said:
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!
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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
 
leefaithfull said:
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
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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!
 
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!
 
leefaithfull said:
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
Click to expand...
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!
 
limeplastering said:
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!
Click to expand...
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!
 
RenovationHelp said:
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!
Click to expand...
RenovationHelp said:
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!
Click to expand...
spoy on
 
RenovationHelp said:
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!
Click to expand...
Where abouts are you based the might be some one on here close by?
 
RenovationHelp said:
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!
Click to expand...
We’ve told previously on this thread that builder of yours is a pee taker and doesn’t know s**t
 
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