Dot and Dab Plasterboard on original barn walls causing problems

[Spoilt Victorian Child]

I sometime even wonder if there is such a thing as 'rising damp' or is just a favoured term to make potential customers quake in their boots and part with their hard earned cash?

You've pretty much hit the nail on the head there. Yes, it's a fake industry that only exists in the UK. Go to some of the wettest cities you can think of (Amsterdam, Venice...) and see if they've got holes drilled along the bottoms of all their buildings which have been literally sitting in water for the past 100+ years.

I mention this guy's site often, but it really opened my eyes. He knows his stuff.
https://www.heritage-house.org/damp-and-condensation/managing-damp-in-old-buildings.html

I have actually used him to survey a property, with excellent advice and (now) dry results.
Look through his YouTube channel for any videos where he inspects damp, especially where a 'damp survey' has already been carried out, and he can usually debunk the survey with common sense, logic and actual scientific proof.
https://www.youtube.com/user/stibnite11/videos

In fact, he goes to a barn conversion that has dry-lined walls in this video, https://www.youtube.com/watch?v=xa_ZPVSP-Qo and finds the relative humidity in the air gap behind the plasterboard is 80-90%! In this case it was due to the outside ground level being higher than the inside.
I think you need to find why it's happened in your place, because even though plastering with lime plaster sounds a good solution, if the source of moisture is still there it could just move to the next 'weak spot'.

Oh, and here's a bit more reading on the 'damp industry' here:
http://www.buildingconservation.com/articles/risingdamp/risingdamp.htm

How thick are the outside walls, BTW?
What is the flooring made of? What would it have been originally?
Was the mortar in the bottom row of (dry) engineering bricks eroded too?

 

[steveb]

also did the damp patches correspond with the dots of plasterboard adhesive? The ones in our new place do...

We're going to take off the plasterboard and let the wall breathe instead of hole up the damp behind it.

 

[Kearn]

All,

Thanks for all your inputs so far. The areas impacted are a walk way to the bedrooms and the bedrooms themselves. I was thinking I could leave the walkway brick exposed, but for the bedrooms I would ideally like some other finish, that is easily manageable for an average DIYer, yet still breathable.
I have also finally worked out how to attach pictures. I had added 3 pictures showing the one brick wall I have exposed so far showing the salt damage, the spalling to the lower course of brick and the missing mortar.
Any further thoughts would be gratefully appreciated!

What looks interesting, at least from what I can see, is the different eras of bricks. From your first couple of pictures, the lowest completely visible coarse of bricks (and below) appears older than those above. Thinner, less uniform and possibly more noticeable remnants of limewash - which would make sense is an animal shelter where plaster wouldn't have been used, and lime wash was seen as protective. Which would imply the wall isn't as old as the base. You'll be able to approximate a date for the wall from the brick bond pattern in which they are built, which I c any quite make out from the image as I can't spot the repeat (if there is one?!).
Lower down it's unlikely lime mortar has disintegrated, more likely someone has raked it out, possibly a bit roughly and damaged the edges of the softer bricks. I can't really see any surface palling as such, certainly none I would be concerned by. Severe instances will see the entire faces of bricks come away in layer after layer, taking off a few mm each time. I can't really see salt deposits either, the white to me looks more like lime from the pics, but hard to tell. Salt tends to come out furry/crystalline in structure and will rub off very easily. Anyway, as others have said, first course of action is strip it back, let it breathe and take note of the dampest (smelliest/or touch) areas and see if you can pinpoint the cause of these symptoms. You'll notice these dramatically start to dry out often noticeably so within a day, then let the wall have a decent run to fully dry out before fixing the problems(s) and deciding on a solution. Unfortunate time of year as the temp means things will be a bit slower...

 

[Spoilt Victorian Child]

You also need to start planning how to get air circulating through this corridor for the long term - it might be as simple as shaving a few mm from under the doors to allow draughts to carry the moisture to a room where it can escape without doing damage.

Are there any windows or is the corridor 'landlocked' by rooms?

 

[lukebasterfield]

All,

Thanks for all your inputs so far. The areas impacted are a walk way to the bedrooms and the bedrooms themselves. I was thinking I could leave the walkway brick exposed, but for the bedrooms I would ideally like some other finish, that is easily manageable for an average DIYer, yet still breathable.
I have also finally worked out how to attach pictures. I had added 3 pictures showing the one brick wall I have exposed so far showing the salt damage, the spalling to the lower course of brick and the missing mortar.
Any further thoughts would be gratefully appreciated!

What looks interesting, at least from what I can see, is the different eras of bricks. From your first couple of pictures, the lowest completely visible coarse of bricks (and below) appears older than those above. Thinner, less uniform and possibly more noticeable remnants of limewash - which would make sense is an animal shelter where plaster wouldn't have been used, and lime wash was seen as protective. Which would imply the wall isn't as old as the base. You'll be able to approximate a date for the wall from the brick bond pattern in which they are built, which I c any quite make out from the image as I can't spot the repeat (if there is one?!).
Lower down it's unlikely lime mortar has disintegrated, more likely someone has raked it out, possibly a bit roughly and damaged the edges of the softer bricks. I can't really see any surface palling as such, certainly none I would be concerned by. Severe instances will see the entire faces of bricks come away in layer after layer, taking off a few mm each time. I can't really see salt deposits either, the white to me looks more like lime from the pics, but hard to tell. Salt tends to come out furry/crystalline in structure and will rub off very easily. Anyway, as others have said, first course of action is strip it back, let it breathe and take note of the dampest (smelliest/or touch) areas and see if you can pinpoint the cause of these symptoms. You'll notice these dramatically start to dry out often noticeably so within a day, then let the wall have a decent run to fully dry out before fixing the problems(s) and deciding on a solution. Unfortunate time of year as the temp means things will be a bit slower...

I have taken a photo of what I think of salt deposits up close, it looks crystaline and appears quite fluffy - when I touch it, it simply falls of the wall. I am surprised by how much there is. I have also attached another photo of the wal layout - any help with understanding what they have done with the brickwork and how old it is would be appreciated! I also took a close up one where you can see the gaps in the lowest level where the mortar seems to be missing, not sure why it would have been raked out and just left though!

I notice the damp patches on the other walls seem to occur due to moisture in the air, probably as the main bathroom does not have an extractor fan, and the general lack of ventiliation and air flow through the corridoor. I am considering a PIV unit to bring fresh air in, which might help the circulation - there are already quite large gaps between the walls in the other rooms! Because of the positioning of the damp patches being where the dabs are, I could only assume it is due to salt in the wall attracting any moisture in the air, rather than damp coming from elsewhere, it certainly cannot be rising damp as its a myth apparently! But what I dont understand are all the white salt deposits on the brickwork - especially if the wall may have been reconstructed from newer bricks when it was convered in the 1980s (we believe the original building to date back to late 19th/early 20th century). Its a puzzle, and I want to ensure I do the right thing for the long term, but theres a lot of dab and dot plasterboard to contend with!

 

[lukebasterfield]

also did the damp patches correspond with the dots of plasterboard adhesive? The ones in our new place do...

We're going to take off the plasterboard and let the wall breathe instead of hole up the damp behind it.

Yes the damp patches do align with the dabs - and I think its attracting moisture from the air. I am certainly not planning to just put plasterboard back on, although I had been recommended to put a membrane on and then put plasterboard back by a number of damp companies, but I just feel that is the right thing to do.

 

[lukebasterfield]

I sometime even wonder if there is such a thing as 'rising damp' or is just a favoured term to make potential customers quake in their boots and part with their hard earned cash?

How thick are the outside walls, BTW?
What is the flooring made of? What would it have been originally?
Was the mortar in the bottom row of (dry) engineering bricks eroded too?

The outside walls are apparently solid 9 inch thick brick according to the survey we had done when we brough the house. The flooring as far as I can tell in the corridoor area is some kind of blue brick, and from a nearby area of floor I have pulled up which was actually just paving slabs with gravel on top originally (as a feature area with some cacti can you believe it!), I believe these bricks are layed on top of about 20cm of sand, with a plastic membrane beneath directly on top of soil, which is what I have noticed in the area with the slabs. Originally the corridoor area would have been outside I believe, and the bedrooms would have been the pigstys - I believe the bedroom areas are actually original concrete or something similar slabs from the original farm building.
The mortar in the bottom row also appears to be eroded along the top and sides (not so much at the bottom of the sides), and I cant see the lower level of mortar due to the floor.

 

[Kearn]

Dot and dab is at least better than full on cement render sticking itself to all the brick faces like something out of Alien!

 

[steveb]

We just discovered that the external render beads had been "dot and dabbed" on with plasterboard adhesive...

 

[Zebra]

It seems that on the lower courses the mortar is little more than soil, is that right? If it has failed, and soil has filled the gaps, that will wick moisture up from the ground, even if we are unsure about the possibility of bricks doing so. Also, if you have a membrane on top of soil, right adjacent to the wall, that will make the ground right next to the the wall much wetter than if there were a breathable floor. Therefore whether "rising damp" is a "myth" or not, it would seem you have moisture coming up from underneath, resulting in spalling and salt deposits.
If you are unwilling to replace the entire floor with a limecrete one, then you could try making a "breathing trench" adjacent to the wall - a strip of breathable flooring which will allow the ground adjacent to the wall be dryer than it is at present. That may help. You could perhaps try it, temporarily, to see if it works.
The damp doesn't look as bad as I had imagined from your first description, so it is possible that increasing breathability will make it go away.
The opposite approach (and you must do one or the other, half measures can lead to the kind of problem you're seeing) ie fully interlapped dpc and dpm, is rather drastic and a bit of a last resort. I had to do it here, I'd tried everything else, and still had wet walls to 400mm or so every time it rained, but in your situation I think I would take up the floor around the edges, peel back the dpm and leave it up so that this part is reversible if you change tactics (I can't remember if you have small children in the house, but this part admittedly might be problematic if you do), repoint the lower courses in hydraulic lime mortar, brush off the salts or maybe apply a salts neutraliser, and then see how it goes for a bit, whether the damp comes back.
The alternative is to insert a proper physical dpc in that wall, fully lapped with the dpm on both sides. This will guarantee that no moisture will come up from underneath, and if you're repointing anyway....... :wink:
But it will cause the floor under the membrane to be wetter, so you'd have to do a proper thorough job, or you'll make it worse elsewhere.